We study the generation of baryon asymmetry as well as dark matter (DM) in an extended reheating period after the end of slow-roll inflation. Within the regime of perturbative reheating, we consider different monomial potential of the inflaton field during reheating era. The inflaton condensate reheats the Universe by decaying into the Standard Model (SM) bath either via fermionic or bosonic decay modes. Assuming the leptogenesis route to baryogenesis in a canonical seesaw framework with three right handed neutrinos (RHN), we consider both the radiation bath and perturbative inflaton decay to produce such RHNs during the period of reheating when the maximum temperature of the SM bath is well above the reheating temperature. The DM, assumed to be a SM gauge singlet field, also gets produced from the bath during the reheating period via UV freeze-in. In addition to obtaining different parameter space for such nonthermal leptogenesis and DM for both bosonic and fermionic reheating modes and the type of monomial potential, we discuss the possibility of probing such scenarios via spectral shape of primordial gravitational waves.

We explore a purely gravitational origin of observed baryon asymmetry and dark matter (DM) abundance from asymmetric Hawking radiation of light primordial black holes (PBH) in presence of a non-zero chemical potential, originating from the space-time curvature. Considering the PBHs are described by a Reissner-Nordström metric, and are produced in a radiation dominated Universe, we show, it is possible to simultaneously explain the matter-antimatter asymmetry along with right DM abundance satisfying bounds from big bang nucleosynthesis, cosmic microwave background and gravitational wave energy density due to PBH density fluctuation. We also obtain the parameter space beyond the semiclassical approximation, taking into account the quantum effects on charged PBH dynamics due to memory burden.

We examine the impact of charged lepton Yukawa equilibration on leptogenesis during gravitational reheating. During the post-inflationary era, the inflaton field is assumed to oscillate around the minimum of a monomial potential, leading to the gravitational production of Standard Model (SM) particles, constituting the radiation bath. The heavy right-handed neutrinos (RHN), responsible for generating baryon asymmetry via leptogenesis, are also produced through graviton-mediated scattering of the homogeneous inflaton field and thermal bath, as well as from the inverse decay of the bath particles. By considering both minimal and non-minimal gravitational contributions to SM, we demonstrate that flavour effects can be safely neglected in the minimal reheating scenario. However, with large non-minimal coupling, these effects may become important, depending on the choice of the RHN mass. We identify the corresponding viable parameter space that satisfies the observed baryon asymmetry in each case.

Dark matter (DM) genesis via Ultraviolet (UV) freeze-in embeds the seed of reheating temperature and dynamics in its relic density. Thus, discovery of such a DM candidate can possibly open the window for post-inflationary dynamics. However, there are several challenges in this exercise, as freezing-in DM possesses feeble interaction with the visible sector and therefore very low production cross-section at the collider. We show that mono-photon (and dilepton) signal at the ILC, arising from DM effective operators connected to the SM field strength tensors, can still warrant a signal discovery. We study both the scalar and fermionic DM production during reheating via UV freeze-in, when the inflaton oscillates at the bottom of a general monomial potential. Interestingly, we see, right DM abundance can be achieved only in the case of bosonic reheating scenario, satisfying bounds from big bang nucleosynthesis (BBN). This provides a unique correlation between collider signal and the post-inflationary dynamics of the Universe within single-field inflationary models.

The transition from the end of inflation to a hot, thermal Universe, commonly referred to as (re)heating, is a critical yet often misunderstood phase in early Universe cosmology. This short review aims to provide a comprehensive, conceptually clear, and accessible introduction to the physics of (re)heating, tailored to the particle physics community. We critically examine the standard Boltzmann approach, emphasizing its limitations in capturing the intrinsically non-perturbative and non-linear dynamics that dominate the early stages of energy transfer. These include explosive particle production, inflaton fragmentation, turbulence, and thermalization; phenomena often overlooked in perturbative treatments. We survey a wide range of theoretical tools, from Boltzmann equations to lattice simulations, clarifying when each is applicable and highlighting scenarios where analytic control is still feasible. Special attention is given to model-dependent features such as (pre)heating, the role of fermions, gravitational couplings, and the impact of multifield dynamics. We also discuss exceptional cases, including Starobinsky-like models and instant (pre)heating, where (re)heating proceeds through analytically tractable channels without requiring full non-linear simulations. Ultimately, this review serves both as a practical guide and a cautionary tale, advocating for a more nuanced and physically accurate understanding of this pivotal epoch within the particle physics community.

In the minimal gauged B − L extension of the Standard Model, we demonstrate that PeV-scale dark matter (DM) and the baryon asymmetry of the Universe (BAU) can be simultaneously explained through the three right-handed neutrinos (RHNs) present in the theory. The DM candidate undergoes rare decay into light neutrinos, providing an explanation for the observed IceCube events, while the other two RHNs generate the BAU via leptogenesis. The breaking of gauge symmetry gives rise to detectable gravitational waves (GWs) from decaying cosmic strings (CS), making this framework testable at several future GW detectors—despite being beyond the reach of conventional collider experiments due to the extremely weak gauge coupling. The symmetry-breaking scale establishes a connection between particle masses, couplings, and the GW spectrum, offering a unified and predictive scenario.

Traditional Planckian Interacting Dark Matter (PIDM), which interacts exclusively through gravity, typically requires heavy DM candidates (with mass 103-1015 GeV) and very high reheating temperature (Trh ≳ 1015 GeV). In this article, we explore a novel realization of PIDM in warped five-dimensions, consisting of an Ultra Violet-Dark-Infra Red (UV-DB-IR) brane setup, where the DM can be a Dark brane composite light state with mass 1 MeV-1 TeV. The DM sector is assumed to interact solely via gravity in five-dimensions. After orbifolding and performing a Kaluza-Klein (KK) decomposition, the DM is assumed to be localized onto the DB, which is positioned in the extra-dimension such that the DM interacts with both the massless graviton and its massive KK excitations, with suppressed couplings to remain consistent with the ethos of the PIDM framework. The light (heavy) Standard Model matter is assumed to be localized near UV (IR) branes for the geometric Froggatt-Neilsen mechanism, while their KK modes are localized close to the IR brane. We show that this construction allows for a viable and efficient freeze-in production mechanism for light composite PIDM, consistent with TeV-scale reheating temperature.

We propose a methodology to infer the reheat temperature (TRH) of the Universe from the collider signal of freezing in dark matter (DM). We demonstrate it for the mono-γ signal at the electron-positron colliders, which indicates to a low-scale TRH, after addressing observed DM abundance, BBN, and other relevant constraints. The method can be used to correlate different reheating dynamics, DM models, and collider signals.

Within the general Uð1Þ scenario, we demonstrate that the ultrahigh-energy neutrinos recently detected by KM3NeT could originate from a decaying right-handed neutrino dark matter, with a mass of 440 PeV. Considering dark matter production via freeze-in, we delineate the parameter space that satisfies the observed relic abundance and also lies within the reach of multiple gravitational wave detectors. Our study provides a testable new physics scenario, enabled by multimessenger astronomy.

We show, within the single-field inflationary paradigm, that a linear non-minimal interaction ξ MP ϕ R between the inflaton field ϕ and the Ricci scalar R can result in successful inflation that concludes with an efficient heating of the Universe via perturbative decays of the inflaton, aided entirely by gravity. Considering the inflaton field to oscillate in a quadratic potential, we find that O(10-1) ≲ O ≲ O(102) is required to satisfy the observational bounds from Cosmic Microwave Background (CMB) and Big Bang Nucleosynthesis (BBN). Interestingly, the upper bound on the non-minimal coupling guarantees a tensor-to-scalar ratio r ≳ 10-4, within the range of current and future planned experiments. We also discuss implications of dark matter production, along with the potential generation of the matter-antimatter asymmetry resulting from inflaton decay, through the same gravity portal.

Assuming axions are potential dark matter (DM) candidate that make up all of the DM abundance, we discuss production of axions via (i) standard misalignment mechanism during the period of reheating and (ii) graviton-mediated 2-to-2 scattering of the inflaton and bath particles, where the inflaton φ oscillates in a monomial potential V(φ)∝φk with a general equation of state. Considering reheating takes place purely gravitationally, mediated by massless gravitons, we explore the viable region of the parameter space that agrees with the observed DM relic abundance, satisfying bounds from big bang nucleosynthesis and cosmic microwave background radiation. We also discuss complementarity between dedicated axion search experiments and futuristic gravitational wave search facilities in probing the viable parameter space, thanks to the presence of detectable primordial gravitational waves with an inflationary origin.

Considering graviton as the only messenger that exists between the inflaton, the dark sector and the Standard Model (SM), we show, it is possible to simultaneously generate the observed relic density of dark matter (DM), the baryon asymmetry via leptogenesis, as well as successful reheating after inflation. Assuming the inflaton ϕ oscillates in a monomial potential V(ϕ) ∝ ϕk at the end of inflation, reheating via minimal gravitational interaction turns out to be excluded due to excessive production of gravitational wave (GW) energy density from inflation. We thus (a) extend the minimal model by considering a non-minimal gravitational contribution to radiation and (b)) propose an explanation for the PeV excess observed by IceCube, when the DM has an explicit Yukawa coupling to the SM leptong and Higgs. We also propose a novel scenario, where the gravitational production is a two-step process, through the production of a pair of scalars, that eventually decay into fermionic final states. Our framework gives rise to detectable primordial GW signal, that falls within the sensitivity of several proposed GW detectors.

We investigate a novel reheating scenario proceeding through s-channel inflaton annihilation, mediated by a massive scalar. If the inflaton ϕ oscillates around the minimum of a monomial potential ∝ ϕ n, we reveal the emergence of resonance phenomena originating from the dynamic evolution of the inflaton mass for n>2. Consequently, a resonance appears in both the radiation and the temperature evolution during the reheating process. By solving the coupled Boltzmann equations, we present solutions for radiation and temperature. We find non-trivial temperature characteristics during reheating, depending on the value of n and the masses of the inflaton and mediator. Some phenomenological aspects of the model are explored. As a concrete example, we show that the same mediator participates in the genesis of dark matter, modifying the standard freeze-in dynamics. In addition, we demonstrate that the resonant reheating scenario could be tested by next-generation low- and high-frequency gravitational wave detectors.

We explore the possibility of producing the observed matter-antimatter asymmetry of the Universe uniquely from the evaporation of primordial black holes (PBHs) that are formed in an inflaton-dominated background. Considering the inflaton (φ) to oscillate in a monomial potential V(φ) φn, we show, it is possible to obtain the desired baryon asymmetry via vanilla leptogenesis from evaporating PBHs of initial mass 10 g. We find that the allowed parameter space is heavily dependent on the shape of the inflaton potential during reheating (determined by the exponent of the potential n), the energy density of PBHs (determined by β), and the nature of the coupling between the inflaton and the Standard Model. To complete the minimal gravitational framework, we also include in our analysis the gravitational leptogenesis setup through inflaton scattering via exchange of graviton, which opens up an even larger window for PBH mass, depending on the background equation of state. We finally illustrate that such gravitational leptogenesis scenarios can be tested with upcoming gravitational wave (GW) detectors, courtesy of the blue-tilted primordial GW with inflationary origin, thus paving a way to probe a PBH-induced reheating together with leptogenesis.

We investigate dark matter (DM-)electron scattering in a minimal U(1)X extension of the Standard Model (SM), where the DM can appear as a Majorana fermion, a complex singlet scalar, or a Dirac fermion. To study bounds on the U(1)X gauge coupling (gX) and new gauge boson mass (MZ′), from DM-electron scattering, we consider several direct search experiments like CDMS, DAMIC, SENSEI, PandaX-II, DarkSide-50, and XENON1T-S2 for different U(1)X charges. In this setup, we consider DM production via freeze-in in both radiation-dominated and modified cosmological background to project sensitivities onto gX-MZ′ plane satisfying observed relic abundance. DM-electron scattering could provide comparable, or even stronger, bounds compared to those obtained from the electron/muon (g-2), low-energy scattering, and intensity frontier experiments within 0.01 GeVMZ′0.1 GeV. Constrains from freeze-in could provide stronger sensitivities for MZ′O(1) GeV; however, these limits are comparable to those obtained from LHCb and LEP experiments for O(10) GeVMZ′150 GeV. In the future, electron-muon scattering (MUonE), proton (FASER and DUNE), and electron/positron (ILC) beam-dump experiments could probe these parameters.

We explore the possibility of explaining the observed dark matter (DM) relic abundance, along with matter-antimatter asymmetry, entirely from the evaporation of primordial black holes (PBH) beyond the semi-classical approximation. We find that, depending on the timing of modification to the semi-classical approximation and the efficiency of the backreaction, it is possible to produce the correct DM abundance for PBHs with masses ≳ O (103) g, whereas producing the right amount of baryon asymmetry requires light PBHs with masses ≲ O (103) g, satisfying bounds on the PBH mass from the Cosmic Microwave Background and Big Bang Nucleosynthesis. However, in a simplistic scenario, achieving both simultaneously is not feasible, typically because of the stringent Lyman-α constraint on warm dark matter mass. In addition to DM and baryon asymmetry, we also investigate the impact of memory burden on dark radiation, evaporated from PBH, constrained by the effective number of relativistic degrees of freedom Δ N eff. Furthermore, we demonstrate how induced gravitational waves from PBH density fluctuations can provide a window to test the memory-burden effects, thereby placing constraints on either the DM mass scale or the scale of leptogenesis.

We investigate the implications of memory burden on the gravitational wave (GW) spectrum arising from the Hawking evaporation of light primordial black holes (PBHs). By considering both rotating (Kerr) and non-rotating (Schwarzschild) PBHs, we demonstrate that the overproduction of primordial GWs from burdened PBHs could impose stringent constraints on the parameters governing backreaction effects. These constraints, derived from ∆Neff measurements by Planck and prospective experiments such as CMB-S4 and CMB-HD, offer novel insights into the impact of memory burden on PBH dynamics.

High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe standard model (SM) processes and search for physics beyond the standard model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential.

We propose a new way of probing the nonthermal origin of baryon asymmetry of the Universe (BAU) and dark matter (DM) from evaporating primordial black holes (PBHs) via stochastic gravitational waves (GWs) emitted due to PBH density fluctuations. We adopt a baryogenesis setup where CP-violating out-of-equilibrium decays of a colored scalar, produced nonthermally at late epochs from PBH evaporation, lead to the generation of BAU. The same PBH evaporation is also responsible for nonthermal origin of superheavy DM. Unlike the case of baryogenesis via leptogenesis that necessarily corners the PBH mass to ∼O(1) g, here we can have PBH mass as large as ∼O(107) g due to the possibility of producing BAU directly below sphaleron decoupling temperature. Because of the larger allowed PBH mass we can also have observable GW with mHz-kHz frequencies originating from PBH density fluctuations keeping the model constrained and verifiable at ongoing as well as near future GW experiments like LIGO, BBO, DECIGO, CE, ET etc. Because of the presence of new colored particles and baryon number violation, the model also has complementary detection prospects at laboratory experiments.

We revisit graviton production via Bremsstrahlung from the decay of the inflaton during inflationary reheating. Using two complementary computational techniques, we first show that such 3-body differential decay rates differ from previously reported results in the literature. We then compute the stochastic gravitational wave (GW) background that forms during the period of reheating, when the inflaton perturbatively decays with the radiative emission of gravitons. By computing the number of relativistic degrees of freedom in terms of Δ N eff, we constrain the resulting GW energy density from BBN and CMB. Finally, we project current and future GW detector sensitivities in probing such a stochastic GW background, which typically peaks in the GHz to THz ballpark, opening up the opportunity to be detected with microwave cavities and space-based GW detectors.

We investigate the reach of future gravitational wave (GW) detectors in probing inflaton couplings with visible sector particles that can either be bosonic or fermionic in nature. Assuming reheating takes place through perturbative quantum production from vacuum in presence of classical inflaton background field, we find that the spectral energy density of the primordial GW generated during inflation becomes sensitive to inflaton-matter coupling. We conclude, obeying bounds from Big Bang Nucleosysthesis and Cosmic Microwave Background, that, e.g., inflaton-scalar couplings of the order of ~ O(10−20) GeV fall within the sensitivity range of several proposed GW detector facilities. However, this prediction is sensitive to the size of the inflationary scale, nature of the inflaton-matter interaction and shape of the potential during reheating. Having found the time-dependent effective inflaton decay width, we also discuss its implications for dark matter (DM) production from the thermal plasma via UV freeze-in during reheating. It is shown, that one can reproduce the observed DM abundance for its mass up to several PeVs, depending on the dimension of the operator connecting DM with the thermal bath and the associated scale of the UV physics. Thus we promote primordial GW to observables sensitive to feebly coupled inflaton, which is very challenging if not impossible to test in conventional particle physics laboratories or astrophysical measurements.

We explore the possibility of probing freeze-in dark matter (DM) produced via the right-handed neutrino (RHN) portal using the RHN search experiments. We focus on a simplified framework of minimally-extended type-I seesaw model consisting of only four free parameters, namely the RHN mass, the fermionic DM mass, the Yukawa coupling between the DM and the RHN, and a real singlet scalar mass. We consider two cases for the DM production either via decay of the thermal RHN or via scattering of the bath particles mediated by the RHN. In both cases, we show that for sub-TeV scale DM masses, the allowed model parameter space satisfying the observed DM relic density for freeze-in scenario falls within the reach of current and future collider, beam dump and forward physics facilities looking for feebly coupled heavy neutrinos.

Motivated by the recent release of new results from five different pulsar timing array (PTA) experiments claiming to have found compelling evidence for primordial gravitational waves (GW) at nano-Hz frequencies, we study the consequences for two popular beyond the Standard Model (SM) frameworks, where such nano-Hz GW can arise due to annihilating domain walls (DW). Minimal framework of Dirac leptogenesis, as well as left-right symmetric model (LRSM) can lead to formation of DW due to spontaneous breaking of Z 2 symmetry. Considering the NANOGrav 15 yr data, we show that the scale of Dirac leptogenesis should be above 107 GeV for conservative choices of Dirac Yukawa couplings with fine-tuning at the level of the SM. The scale of minimal LRSM is found to be more constrained M LR ∼ 106 GeV in order to fit the NANOGrav 15 yr data. On the other hand, the non-minimal LRSM can be compatible with the NANOGrav data for 102 TeV ≲ M LR ≲ 103 TeV but with the corresponding B - L breaking scale violating collider bounds.

We discuss the production of primordial gravitational waves (GW) from radiative inflaton decay during the period of reheating, assuming perturbative decay of the inflaton either into a pair of bosons or fermions, leading to successful reheating satisfying constraint from big bang nucleosynthesis. Assuming that the inflaton φ oscillates in a general monomial potential V(φ)∝φn, which results in a time-dependent inflaton decay width, we show that the resulting stochastic GW background can have optimistic detection prospects, especially in detectors that search for a high-frequency GW spectrum, depending on the choice of n that determines the shape of the potential during reheating. We also discuss how this GW energy density may affect the measurement of ΔNeff for bosonic and fermionic reheating scenarios.

We consider a simple abelian vector dark matter (DM) model, where only the DM (Xμ) couples non-minimally to the scalar curvature (R) of the background spacetime via an operator of the form 1/4Xμ Xμ R. By considering the standard freeze-out scenario, we show, it is possible to probe such a non-minimally coupled DM in direct detection experiments for a coupling strength ζ 1/4o ' (1030) and DM mass m X 2 55 TeV, satisfying Planck observed relic abundance and perturbative unitarity. We also discuss DM production via freeze-in, governed by the non-minimal coupling, that requires ζ 210-5 to produce the observed DM abundance over a large range of DM mass depending on the choice of the reheating temperature. We further show, even in the absence of the non-minimal coupling, it is possible to produce the whole observed DM abundance via 2-to-2 scattering of the bath particles mediated by massless gravitons.

We study the possibility of cogenesis of baryon and dark matter (DM) from the out-of-equilibrium CP violating decay of right handed neutrino (RHN) that are dominantly of non-thermal origin. While the RHN and its heavier partners can take part in light neutrino mass generation via Type-I seesaw mechanism, the decay of RHN into dark and visible sectors can create respective asymmetries simultaneously. The non-thermal sources of RHN considered are (a) on-shell decay of inflaton, and (b) evaporation of ultralight primordial black holes (PBH). After setting up the complete set of Boltzmann equations in both these scenarios, we constrain the resulting parameter space of the particle physics setup, along with inflaton and PBH sectors from the requirement of generating correct (asymmetric) DM abundance and baryon asymmetry, while being in agreement with other relevant cosmological bounds. Scenario (a) links the common origin of DM and baryon asymmetry to post-inflationary reheating via RHNs produced in inflaton decay, whereas in scenario (b) we find enhancement of baryon and DM abundance, compared to the purely thermal scenarios, in presence of PBH with appropriate mass and initial fraction. Although the minimal setup itself is very predictive with observational consequences, details of the UV completion of the dark sector can offer several complementary probes.

We study the freeze-in production of vector dark matter (DM) in a classically scale invariant theory, where the Standard Model (SM) is augmented with an abelian U(1) X gauge symmetry that is spontaneously broken due to the non-zero vacuum expectation value (VEV) of a scalar charged under the U(1) X . Generating the SM Higgs mass at 1-loop level, it leaves only two parameters in the dark sector, namely, the DM mass mX and the gauge coupling gX as independent, and supplement with a naturally light dark scalar particle. We show, for gX ∼ O(10-5), it is possible to produce the DM X out-of-equilibrium in the early Universe, satisfying the observed relic abundance for mX ∼ O(TeV), which in turn also determines the scalar mixing angle sinθ ∼ O(10-5). The presence of such naturally light scalar mediator with tiny mixing with the SM, opens up the possibility for the model to be explored in direct search experiment, which otherwise is insensitive to standard freeze-in scenarios. Moreover we show that even with such feeble couplings, necessary for the DM freeze-in, the scenario is testable in several light dark sector searches (e.g., in DUNE and in FASER-II), satisfying constraints from the observed relic abundance as well as big bang nucleosynthesis (BBN). Particularly, we find, regions in the parameter space with mX ≲ 1.8 TeV becomes insensitive to direct detection probe but still can be accessible in lifetime frontier searches, again courtesy to the underlying scale invariance of the theory.

We consider higher-dimensional effective (EFT) operators consisting of fermion dark matter (DM) connecting to Standard Model (SM) leptons upto dimension six. Considering all operators together and assuming the DM to undergo thermal freeze-out, we find out relic density allowed parameter space in terms of DM mass (mχ) and New Physics (NP) scale (Λ) with one loop direct search constraints from XENON1T experiment. Allowed parameter space of the model is probed at the proposed International Linear Collider (ILC) via monophoton signal for both Dirac and Majorana cases, limited by the centre-of-mass energy s =1 TeV, where DM mass can be probed within mχ<s2 for the pair production to occur and Λ >s for the validity of EFT framework.

It is typically assumed that during reheating the inflaton decays with a constant decay width. However, this is not guaranteed and can have a strong impact on the dark matter (DM) genesis. In the context of the ultraviolet (UV) freeze-in mechanism, if the operators connecting the dark and visible sectors are of sufficiently high mass dimension, the bulk of the DM abundance is produced during and not after reheating. We study here the impact of a time-dependent decay width of the inflaton on the DM abundance, emphasizing the differences with respect to the cases where the decay is either instantaneous or constant. We also provide concrete examples for DM production via UV freeze-in, e.g., from 2-to-2 scatterings of standard model particles, or from inflaton scatterings or decays, elucidating how the time-dependence influences the DM yield.

We propose a novel way of probing high-scale Dirac leptogenesis, a viable alternative to the canonical leptogenesis scenario where the total lepton number is conserved, keeping light standard model neutrinos purely Dirac. The simplest possible seesaw mechanism for generating light Dirac neutrinos involves heavy singlet Dirac fermions and a singlet scalar. In addition to unbroken global lepton number, a discrete Z2 symmetry is imposed to forbid direct coupling between right and left chiral parts of light Dirac neutrinos. Generating light Dirac neutrino mass requires the singlet scalar to acquire a vacuum expectation value (VEV) that also breaks the Z2 symmetry, leading to the formation of domain walls in the early Universe. These walls, if made unstable by introducing a soft Z2-breaking term, generate gravitational waves (GWs) with a spectrum characterized by the wall tension or the singlet VEV, and the soft symmetry breaking scale. The scale of leptogenesis depends on the Z2-breaking singlet VEV, which is also responsible for the tension of the domain wall, affecting the amplitude of GWs produced from the collapsing walls. We find that most of the near-future GW observatories will be able to probe Dirac leptogenesis scales all the way up to 1011 GeV.

We consider a singlet fermionic dark matter (DM) χ in a gauged U(1)B-3L i extension of the Standard Model (SM), with i 2 e, μ, τ, and derive bounds on the allowed parameter space, considering its production via freeze-in mechanism. The DM communicates with the SM only through flavorful vector-portal Z B3L due to its non-trivial charge x under U(1)B-3L i, which also guarantees the stability of the DM over the age of the Universe for x ≠ {±3/2, ±3}. Considering Z B3L to lie within the mass range of a few MeV up to a few GeV, we obtain constraints on the gauge coupling g B3L from the requirement of producing right relic abundance. Taking limits from various (present and future) experimental facilities, e.g., NuCal, NA64, FASER, SHiP into account, we show that the relic density allowed parameter space for the frozen in DM can be probed with g B3L ≳ 10-8 for both mχ < m ZB3L/2 and mχ ≳ m ZB3L, while g B3L ≲ 10-8 remains mostly unconstrained. We also briefly comment on the implications of neutrino mass generation via Type-I seesaw and anomalous (g-2) μ in context with B-3Lμ gauged symmetry.

We propose a scenario where dark matter (DM) with a wide mass range from a few keV to PeV can be produced solely from evaporating primordial black holes (PBH), while being consistent with the required free streaming length for structure formation. If DM does not have any other interactions apart from gravity and the universe has a PBH dominated phase at early epoch, then PBH evaporation typically leads to overproduction of DM in this mass range. By incorporating this gravitational DM within a Type-I seesaw scenario with three right handed neutrinos (RHN), we bring the abundance of PBH generated DM within observed limits by late entropy injection due to decay of one of the RHNs, acting as the diluter. The diluter, due to its feeble coupling with the bath particles, gets produced primarily from the PBH evaporation thereby leading to the second stage of early matter domination after the end of PBH dominated era. The other two RHNs contribute to the origin of light neutrino mass and also lead to the observed baryon asymmetry via leptogenesis with contributions from both thermally and PBH generated RHNs. The criteria of DM relic and baryon asymmetry can be satisfied simultaneously if DM mass gets restricted to a ballpark in the MeV-GeV regime with the requirement of resonant leptogenesis for heavier DM mass in order to survive the large entropy dilution at late epochs.

Detecting dark matter (DM) relic via freeze-in is difficult in laboratories due to smallness of the couplings involved. However, a non-standard cosmological history of the Universe, prior to Big Bang Nucleosynthesis (BBN), can dramatically change this scenario. In this context, we study the freeze-in production of dark matter (DM) in classically scale invariant U(1) X gauge extension of the Standard Model (SM), recently dubbed as the Scale Invariant FIMP Miracle. We assume an additional species dominates the energy density of the Universe at early times, causing the expansion rate at a given temperature to be larger than that in the standard radiation-dominated case. We find, the out-of-equilibrium scattering processes involving particles in the thermal bath lead to significantly suppressed DM production in this era, thereby enhancing the couplings between the visible and the dark sector (by several orders of magnitude) to satisfy the observed DM abundance, and improving the detection prospects for freeze-in in turn. Scale invariance of the underlying theory leaves only four free parameters in the model: the DM mass mX , the gauge coupling gX , the temperature of transition TR from early scalar-dominated to radiation-dominated era and the power-law dependence n of this temperature. We show, within this minimal set-up, experiments like FASER, MATHUSLA, DUNE, SHiP will be probing various cosmological models depending on the choice of {n, TR } that also satisfy the PLANCK observed relic density bound. Moreover, due to the presence of a naturally light scalar mediator, the direct detection of the DM at XENON1T, PandaX-4T or XENONnT becomes relevant for Higgs-scalar mixing sinθ ≃ {10-5-10-3}, thus providing complementary probes for freeze-in, as well as for non-standard cosmological pre-BBN era.

We show that a minimal scenario, utilizing only the graviton as an intermediate messenger between the inflaton, the dark sector and the Standard Model (SM), is able to generate simultaneously the observed relic density of dark matter (DM), the baryon asymmetry through leptogenesis, as well as a sufficiently hot thermal bath after inflation. We assume an inflaton potential of the form V(ϕ) ∝ ϕk about the minimum at the end of inflation. The possibility of reheating via minimal gravitational interactions has been excluded by constraints on dark radiation for excessive gravitational waves produced from inflation. We thus extend the minimal model in several ways: i) we consider non-minimal gravitational couplings — this points to the parameter range of DM masses MN1 ≃ 2–10 PeV, and right-handed neutrino masses MN2 ≃ (5–20) × 1011 GeV, and TRH ≲ 3 × 105 GeV (for k ≤ 20); ii) we propose an explanation for the PeV excess observed by IceCube when the DM has a direct but small Yukawa coupling to the SM; and iii) we also propose a novel scenario, where the gravitational production of DM is a two-step process, first through the production of two scalars, which then decay to fermionic DM final states. In this case, the absence of a helicity suppression enhances the production of DM and baryon asymmetry, and allows a great range for the parameters including a dark matter mass below an MeV where dark matter warmness can be observable by cosmic 21-cm lines, even when gravitational interactions are responsible for reheating. We also show that detectable primordial gravitational wave signals provide the opportunity to probe this scenario for TRH ≲ 5 × 106 GeV in future experiments, such as BBO, DECIGO, CE and ET.

The axion field, the angular direction of the complex scalar field associated with the spontaneous symmetry breaking of the Peccei–Quinn (PQ) symmetry, could have originated with initial non-zero velocity. The presence of a non-zero angular velocity resulting from additional terms in the potential that explicitly break the PQ symmetry has important phenomenological consequences such as a modification of the axion mass with respect to the conventional PQ framework or an explanation for the observed matter-antimatter asymmetry. We elaborate further on the consequences of the “kinetic misalignment” mechanism, assuming that axions form the entirety of the dark matter abundance. The kinetic misalignment mechanism possesses a weak limit in which the axion field starts to oscillate at the same temperature as in the conventional PQ framework, and a strong limit corresponding to large initial velocities which effectively delay the onset of oscillations. Following a UV-agnostic approach, we show how this scenario impacts the formation of axion miniclusters, and we sketch the details of these substructures along with potential detecting signatures.

We study the impact of thermalization and number-changing processes in the dark sector on the yield of gravitationally produced dark matter (DM). We take into account the DM production through the s-channel exchange of a massless graviton both from the scattering of inflatons during the reheating era, and from the Standard Model bath via the UV freeze-in mechanism. By considering the DM to be a scalar, a fermion, and a vector boson we show, in a model-independent way, that DM self-interaction gives rise to a larger viable parameter space by allowing lower reheating temperature to be compatible with Planck observed relic abundance. As an example, we also discuss our findings in the context of the 2-symmetric scalar singlet DM model.

We examine the impact of a faster expanding Universe on the phenomenology of scalar dark matter (DM) associated with multiplets. Earlier works with a radiation dominated Universe have reported the presence of desert region for both inert doublet and triplet DM candidates where the DM is underabundant. We find that the existence of a faster expanding component before big bang nucleosynthesis can revive a substantial part of the desert parameter space consistent with relic density requirements and other direct and indirect search bounds. We also review the possible collider search prospects of the newly obtained parameter space and predict that such region might be probed at the future colliders with improved sensitivity via a disappearing/stable charged track.

We study a minimal scenario to realize nonthermal leptogenesis and UV freeze-in of a Standard Model (SM) gauge singlet fermionic dark matter (DM) simultaneously, with inflaton field playing a nontrivial role in their yields. The renormalizable interactions are restricted to the SM fields, two right-handed neutrinos (RHN) and inflaton coupling exclusively to the RHNs, while the DM couples to both the SM and the RHNs only via operators of dimension d>4. Considering two separate cases of d={5,6}, we show that for d=5, inflaton decay into RHNs followed by their subsequent decay into SM particles lead to both reheating as well as DM production from the SM bath. This requires a cut off scale as large as Λ∼1017 GeV depending on the DM mass. On the other hand, for d=6, DM production happens directly from scattering of RHNs (for Λ1014 GeV) that results in a very nontrivial evolution of the DM yield. In both these cases, it is possible to explain the observed baryon asymmetry through successful nonthermal leptogenesis via the decay of the RHNs, together with the Planck observed relic density of the DM via pure UV freeze-in mechanism. Taking into account both instantaneous as well as noninstantaneous reheating separately, we constrain the parameter space of this minimal scenario from relevant phenomenological requirements including sub-eV scale active neutrino masses and their mixing.

We present a study of singlet-doublet vectorlike leptonic dark matter (DM) in the framework of the two-Higgs-doublet model (2HDM), where the dark sector is comprised of one doublet and one singlet vectorlike fermion (VLF). The DM, that arises as an admixture of the neutral components of the VLFs, is stabilized by an imposed discrete symmetry Z2′. We test the viability of the DM candidate in the light of observations from Planck and recent limits on spin-independent direct detection experiments and search for its possible collider signals. In addition, we also look for the stochastic gravitational wave (GW) signatures resulting from strong first-order phase transition due to the presence of the second Higgs doublet. The model thus offers a viable parameter space for a stable DM candidate that can be probed from direct search, collider, and GW experiments.

In this analysis we demonstrate the freeze-in realization of a non-abelian vector boson dark matter (DM). We choose to elaborate an existing SU(2)N extension (N stands for neutral) of the Standard Model (SM) with an additional U(1)=S′ global symmetry, which stabilizes the vector boson (X,) as DM through unbroken S=T3N+S′ as the lightest odd S particle. Apart from showing the right order of the SU(2)N coupling (∼ 10-12-10-13) required for the correct relic of DM via freeze in, the analysis reveals that the contribution to the freeze-in production of DM from the decay of a heavier scalar bi-doublet ζ1 0,± ζ2 0,±X is equally important even after the decoupling of ζ1 0,± from the thermal bath. This treatment of computing the relic abundance in context with freeze-in is practically model-independent and can be applied to all the scenarios where the DM is produced from the decay of a massive particle which was once in equilibrium with the thermal bath. This bi-doublet earlier was in equilibrium with the visible sector due to SM SU(2)L coupling. Moreover, the neutral component of SU(2)N scalar triplet (Δ), responsible for neutrino mass generation in this framework, turns out to serve as additional DMs in the model and offers a multipartite freeze-in DM set up to explore. The allowed parameter space is obtained after estimating constraints from CMB, BBN and AMS-02 bound. This exercise nicely complements the freeze-out realization of (X,) as weakly interacting massive particle (WIMP) and distinguishes it through stable charge track signature at collider compared to leptonic signal excess as in WIMP scenario.

We present a minimal model of fermionic dark matter (DM), where a singlet Dirac fermion can interact with the Standard Model (SM) particles via the torsion field of gravitational origin. In general, torsion can be realized as an antisymmetric part of the affine connection associated with the spacetime diffeomorphism symmetry and thus can be thought of as a massive axial vector field. Because of its gravitational origin, the torsion field couples to all the fermion fields including the DM with equal strength, which makes the model quite predictive. The DM is naturally stable without any imposition of ad hoc symmetry, e.g., Z2. Apart from producing the correct thermal abundance, a singlet fermion can easily evade the stringent bounds on the spin-independent DM-nucleon direct detection cross section due to its axial nature. However, in the allowed parameter space, strong bounds can be placed on the torsion mass and its couplings to fermions from the recent LHC searches. Assuming a nonuniversal torsion-DM and torsion-SM coupling, smaller values of torsion masses may become allowed. In both cases we also study the reach of spin-dependent direct detection searches of the DM.

We perform a model independent study of freeze-in of massive particle dark matter (DM) by adopting an effective field theory framework. Considering the dark matter to be a gauge singlet Majorana fermion, odd under a stabilising symmetry Z2 under which all standard model (SM) fields are even, we write down all possible DM-SM operators upto and including mass dimension eight. For simplicity of the numerical analysis we restrict ourselves only to the scalar operators in SM as well as in the dark sector. We calculate the DM abundance for each such dimension of operator considering both UV and IR freeze-in contributions which can arise before and after the electroweak symmetry breaking respectively. After constraining the cut-off scale and reheat temperature of the universe from the requirement of correct DM relic abundance, we also study the possibility of connecting the origin of neutrino mass to the same cut-off scale by virtue of lepton number violating Weinberg operators. We thus compare the bounds on such cut-off scale and corresponding reheat temperature required for UV freeze-in from the origin of light neutrino mass as well as from the requirement of correct DM relic abundance. We also briefly comment upon the possibilities of realising such DM-SM effective operators in a UV complete model.

A model of dark matter (DM) that communicates with the Standard Model (SM) exclusively through suppressed dimension five operator is discussed. The SM is augmented with a symmetry U(1)X ⊗ Z2, where U(1)X is gauged and broken spontaneously by a very heavy decoupled scalar. The massive U(1)X vector boson (Xμ) is stabilized being odd under unbroken Z2 and therefore may contribute as the DM component of the universe. Dark sector field strength tensor Xμν couples to the SM hypercharge tensor Bμν via the presence of a heavier Z2 odd real scalar Φ, i.e. 1/Λ XμνBμνΦ, with Λ being a scale of new physics. The freeze-in production of the vector boson dark matter feebly coupled to the SM is advocated in this analysis. Limitations of the so-called UV freeze-in mechanism that emerge when the maximum reheat temperature TRH drops down close to the scale of DM mass are discussed. The parameter space of the model consistent with the observed DM abundance is determined. The model easily and naturally avoids both direct and indirect DM searches. Possibility for detection at the Large Hadron Collider (LHC) is also considered. A Stueckelberg formulation of the model is derived.

Fermion dark matter (DM) as an admixture of additional singlet and doublet vectorlike fermions provides an attractive and allowed framework by relic density and direct search constraints within TeV scale, although limited by its discovery potential at the Large Hadron Collider (LHC) excepting for a displaced vertex signature of charged vectorlike lepton. An extension of the model with the scalar triplet can yield neutrino masses and provide some cushion to the direct search constraint of the DM through pseudo-Dirac mass splitting. This in turn, allows the model to live in a larger region of the parameter space and open the door for detection at LHC through hadronically quiet dilepton channel, even if slightly. We also note an interesting consequence to the hadronically quiet four lepton signal produced by the doubly charged scalar belonging to the triplet, in the presence of additional vectorlike fermions as in our model. The model however can see an early discovery at International Linear Collider (ILC) without too much of fine-tuning. The complementarity of LHC, ILC and direct search prospect of this framework is studied in this paper.

We propose an Abelian gauged version of the singlet-doublet fermionic dark matter (DM) model where the DM, combination of a vector like fermion doublet and a fermion singlet, is naturally stabilised by the gauge symmetry without requiring any ad-hoc discrete symmetries. In order to have an enlarged parameter space for the DM, accsessible at collider experiments like the Large Hadron Collider (LHC), we consider the additional gauge symmetry to be based on the quantum B − 3Lτ. The restriction to third generation of leptons is chosen in order to have weaker bounds from the LHC on the corresponding gauge boson. The triangle anomalies arising in this model can be cancelled by the inclusion of a right handed neutrino which also takes part in generating light neutrino masses through type I seesaw mechanism. The model thus offers a potential thermal DM candidate, interesting collider signatures and correct neutrino mass along with a stable electroweak vacuum and perturbative couplings all the way up to the Planck scale. We constrain our model parameters from these requirements as well as existing relevant constraints related to DM and colliders.

In this article, we have considered an extension of the inert Higgs doublet model with SU(2)L singlet vectorlike fermions. Our model is capable of addressing some interesting anomalous results in b→sâ.,"+â.,"-decays [like R(K(∗))] and in muon (g-2). Apart from explaining these anomalies, and being consistent with other flavor data, the model satisfies relevant constraints in the dark matter sector, while remaining within the reach of ongoing direct detection experiments. The model also produces signatures at the large hadron collider (LHC) with final states comprised of dilepton, dijet and missing energy, providing signals to be probed at higher luminosity.

Vector boson dark matter (DM) appears in SU(2)N extension (N stands for neutral) of Standard Model (SM) where an additional global U(1)P symmetry is assumed and results in a generalized lepton number defined as: L = P +T3N. Breaking of U(1)P leads to the breaking of L to (−1)L, thus stabilizing DM through modified R = (−1)3B+L+2J. This model, already discussed in literature, offers several novel features to elaborate upon. For example, tchannel annihilation and dominant s-channel direct search, along with co-annihilation, helps the DM to evade stringent direct search bounds from LUX and XENON1T after satisfying relic density constraints. On the other hand, the exotic particles of the model can be produced at the Large Hadron Collider (LHC) yielding multilepton final states. Hadronically quiet four lepton signal with large missing energy, in specific, is shown to provide a smoking gun signature of such a framework. We study the details of E(6) → SM SU(2)N breaking patterns (through D-parity odd/even cases) which yield important phenomenological consequences.