Luc Darmé, Andrzej Hryczuk, Dimitrios Karamitros, Leszek Roszkowski
We study the importance of a frozen-in dark matter production regime, where the dark matter particle is produced via kinematically forbidden decays that arise from significant thermal correction to the mass a mediator particle in the plasma.
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We examine a scenario for freeze-in production of dark matter, which occurs due to the large thermal correction to the mass of a decaying mediator particle present in the thermal bath of the early Universe. We show that the decays, which are kinematically forbidden otherwise, can open up at very high temperatures and dominate the dark matter production. We explore such forbidden production of dark matter in the minimal $U(1)_{B-L}$ model, comparing dark matter phenomenology in the context of forbidden frozen-in with the standard picture.
Scattering versus Forbidden Decay in Dark Matter Freeze-in
本研究揭示热等离子体中禁戒衰变产生重粒子时散射与衰变耦合阶数相同的规律，通过轻标量媒介子暗物质冻结过程验证了二者贡献的相对关系，该效应可推广至其他等离子体诱导过程。
Dark matter freeze-in via a light fermion mediator: forbidden decay and scattering
本文研究通过轻费米子媒介体的冻结暗物质产生，发现禁戒衰变与散射共享耦合阶数，且其贡献在热耦合0.1-1时可达4%-45%。
We consider a model of two-component dark matter based on a hidden $U(1)_D$ symmetry, in which relic densities of the dark matter are determined by forbidden channels and thermal freeze-out. The hidden $U(1)_D$ symmetry is spontaneously broken to a residual $\mathbb{Z}_4$ symmetry, and the lightest $\mathbb{Z}_4$ charged particle can be a dark matter candidate. Moreover, depending on the mass hierarchy in the dark sector, we have two-component dark matter. We show that the relic density of the lighter dark matter component can be determined by forbidden annihilation channels which require larg…
We examine and point out the importance of a regime of dark matter production through the freeze-in mechanism that results from a large thermal correction to a decaying mediator particle mass from hot plasma in the early Universe. We show that mediator decays to dark matter that are kinematically forbidden at the usually considered ranges of low temperatures can be generically present at higher temperatures and actually dominate the overall dark matter production, thus leading to very distinct solutions from the standard case. We illustrate these features by considering a dark Higgs portal mod…
In this review, we focus on dark matter production from thermal freeze-out with forbidden channels and SIMP processes. We show that forbidden channels can be dominant to produce dark matter depending on the dark photon and / or dark Higgs mass compared to SIMP.
Kinematically forbidden channels can set the freeze-out dark matter (DM) relic abundance. These channels are described by DM annihilations into heavier states, which vanish at zero temperature limit, but occur at finite temperatures in the early Universe. For the case that the final state of the forbidden channel is scalar mediators that couple to Standard Model (SM) matter through mixing with the SM Higgs, the signals from DM-nucleon interactions and from mediator-related missing energy or displaced vertices could be detected by direct detections and particle physics experiments, respectively…
At the tail of its velocity distribution, cold dark matter (DM) can annihilate at finite temperature to states heavier than itself. We explore the possibility that DM freezeout is dictated by these "forbidden annihilations" at the electroweak scale. Demanding that annihilation products be Standard Model particles, we find that for the forbidden mechanism to primarily set the DM relic abundance, DM must couple predominantly, if not solely, to top quarks. This can be arranged by invoking a non-trivial flavor structure such as Minimal Flavor Violation. We avail two avenues to achieve the correct …
In a hadronic gas with three conserved charges (electric charge, baryon number, and strangeness) we employ the hadron resonance gas model to compute both diagonal and off-diagonal susceptibilities. We model the effect of chemical freeze-out in two ways: one in which all particle numbers are conserved below the chemical freeze-out temperature and one which takes into account resonance decays. We then briefly discuss possible implications these results may have on two active areas of research, hydrodynamic fluctuations and the search for the QCD critical point.
As experimental searches for WIMP dark matter continue to yield null results, models beyond the WIMP paradigm have proliferated in order to elude ever improving observational constraints, among them that of sub-GeV dark matter mediated by a massive vector portal (a dark photon) associated with a new dark $U(1)$ gauge symmetry. It has been previously noted that for a significant range of the parameter space of this class of models, the annihilation of dark matter particles into a pair of dark photons can dominate the freeze-out process even when this process is kinematically forbidden for dark …
If the interaction rates between the visible and the dark sectors were never strong enough, the observed dark matter relic abundance could have been produced in the early Universe by non-thermal processes. This is what occurs in the so-called freeze-in mechanism. In the simplest version of the freeze-in paradigm, after dark matter is produced from the standard model thermal bath, its abundance is frozen and remains constant. However, thermalization and number-changing processes in the dark sector can have strong impacts, in particular enhancing the dark matter relic abundance by several orders…
We perform a detailed study of dark matter production via freeze-in under the assumption that some fluid dominates the early Universe before depositing its energy to the plasma causing entropy injection. As a dark matter candidate we consider a fermionic singlet that is produced through its interactions with a scalar particle in the thermal plasma. The fluid alters the expansion rate of the Universe, as well as the scaling of the temperature, which significantly affects the evolution of both the number density and the mean momentum of the dark matter particle. We identify and discuss in detail…
Roadmap to Thermal Dark Matter Beyond the WIMP Unitarity Bound
本文解析推广任意热冻结过程的遗迹丰度关系与暗物质质量幺正性界限，指出超越类 WIMP 上限意味着近简并态和亚稳暗物质，质量可至普朗克标度。
We study observational consequences arising from dark matter (DM) of non-thermal origin, produced by dark freeze-out from a hidden sector heat bath. We assume this heat bath was populated by feebly-coupled mediator particles, produced via a Higgs portal interaction with the Standard Model (SM). The dark sector then attained internal equilibrium with a characteristic temperature different from the SM photon temperature. We find that even if the coupling between the DM and the SM sectors is very weak, the scenario allows for indirect observational signals. We show how the expected strength of th…
Thermally corrected masses and freeze-in dark matter: a case study
本文在符合缪子 $(g-2)$ 数据的最小扩展 $U(1)_{L_μ-L_τ}$ 框架中研究标量暗物质的冻结产生，强调高温热质量修正可开启标准情形下运动学禁戒的产生道。
We present an overview of scenarios where the observed Dark Matter (DM) abundance consists of Feebly Interacting Massive Particles (FIMPs), produced non-thermally by the so-called freeze-in mechanism. In contrast to the usual freeze-out scenario, frozen-in FIMP DM interacts very weakly with the particles in the visible sector and never attained thermal equilibrium with the baryon-photon fluid in the early Universe. Instead of being determined by its annihilation strength, the DM abundance depends on the decay and annihilation strengths of particles in equilibrium with the baryon-photon fluid, …
New Production Mechanism for keV Sterile Neutrino Dark Matter by Decays of Frozen-In Scalars
我们提出了一种新的keV无菌中微子暗物质产生机制。在我们的设置中，我们假设存在一个标量单线态粒子，它在早期宇宙中从未进入热平衡，因为它只通过一个非常小的希格斯门相互作用耦合到标准模型场。对于合适的耦合值，标量可以经历所谓的冻结过程，并以这种方式在早期宇宙中有效地产生。然后这些标量衰变成keV的无菌中微子，并产生正确的暗物质丰度。虽然类似的设置中的标量没有进入热平衡，然后冻结之前已经研究过，这里提出的机制是新的，并代表了一个通用的扩展已知的情况。我们进行了详细的数值计算DM生产使用一组耦合玻尔兹曼方程，我们说明了成功的区域中的参数空间。我们的生产机制甚至可以在完全不存在活性-无菌混合的模型中工作。
Freeze-in through portals
暗物质（DM）生产的流行冻结范式依赖于弱相互作用量级的DM-重子耦合。然而，不同的搜索策略DM未能提供这样的（非引力）相互作用的确凿证据，同时大大减少了许多代表性的模型的参数空间。这激发了对DM发生的替代机制的研究。在冻结框架中，DM从热浴中缓慢地填充，而从未达到平衡。在这项工作中，我们详细分析的可能性，生产冻结的DM通过介质粒子作为门户网站。我们给出了不同的冻结制度的分析估计，并支持他们与充分的数值分析，考虑到适当的分布函数浴粒子。最后，我们约束参数空间的通用模型，要求与DM遗迹丰度观测。
Testing frozen-in pNGB dark matter with a long-lived dark Higgs
该研究通过冻结机制探讨暗物质候选者，分析其在LHC和未来对撞机上的探测前景，强调再加热动态对暗物质生产的影响。
Forbidden conformal dark matter at a GeV
提出一种由自发破缺共形场论构成的禁戒暗物质模型，其在5D对偶描述下与0.1-10 GeV质量约束相容，且共形相变可产生NANOGrav观测到的引力波信号，未来实验可探测其参数空间。
We propose a minimal model to simultaneously account for a realistic neutrino spectrum through a type-I seesaw mechanism and a viable dark matter relic density. The model is an extension of the Littlest Seesaw model in which the two right-handed neutrinos of the model are coupled to a $Z_2$-odd dark sector via right-handed neutrino portal couplings. In this model, a highly constrained and direct link between dark matter and neutrino physics is achieved by considering the freeze-in production mechanism of dark matter. We show that the neutrino Yukawa couplings which describe neutrino mass and m…
Sterile neutrinos are one of the leading dark matter candidates. Their masses may originate from a vacuum expectation value of a scalar field. If the sterile neutrino couplings are very small and their direct coupling to the inflaton is forbidden by the lepton number symmetry, the leading dark matter production mechanism is the freeze-in scenario. We study this possibility in the neutrino mass range up to 1 GeV, taking into account relativistic production rates based on the Bose-Einstein statistics, thermal masses and phase transition effects. The specifics of the production mechanism and the …
In an earlier work, we showed that in very simple neutrino portal-like extensions of the Standard Model it is possible to achieve a one-to-one correspondence between dark matter physics and the seesaw parameters controlling the genesis of neutrino masses. Notably, this can occur both when the dark matter is produced via freeze-in and relativistic freeze-out. In this article, we carry out a detailed phenomenological study of such scenarios. Specifically, we find the allowed regions for the neutrino portal coupling within which the correspondence is valid. We further constrain the parameter spac…
We consider a singlet fermionic dark matter (DM) $χ$ in a gauged $U(1)_{B-3L_i}$ extension of the Standard Model (SM), with $i\in e\,,μ\,,τ$, 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 $Z_\text{B3L}$ 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 $x\neq\{\pm 3/2,\pm 3\}$. Considering $Z_\text{B3L}$ to lie within the mass range of a few MeV up to a few GeV, we obtain constraints …
Right-Handed Neutrino Dark Matter with Forbidden Annihilation
本文研究三右手中微子跷跷板模型中的稳定右手中微子暗物质，通过引入额外玻色子ϕ使其经禁戒湮灭通道热冻结，并指出该通道可被银心超大质量黑洞重新激活；Fermi-LAT数据和遗迹密度要求其质量低于100 GeV，且ϕ可在未来轻子对撞机上检验。
If the dark matter is produced in the early universe prior to Big Bang nucleosynthesis, a modified cosmological history can drastically affect the abundance of relic dark matter particles. Here, we assume that an additional species to radiation dominates at early times, causing the expansion rate at a given temperature to be larger than in the standard radiation-dominated case. We demonstrate that, if this is the case, dark matter production via freeze-in (a scenario when dark matter interacts very weakly, and is dumped in the early universe out of equilibrium by decay or scattering processes …
Freeze-out of strange hadrons at RHIC
在微观输运模型下研究了RHIC能区Au+Au碰撞中产生的奇异粒子的产生和冻结条件。最终粒子的系统可以表示为核心，包含仍然相互作用的粒子，以及一个光环，其中粒子已经从系统中解耦。在微观计算中，强子从整个反应体积中连续发射。然而，在RHIC中，很大一部分介子和重子都是从前两个fm/c内的表面区域发射的。不同的物种在不同的时间分离。奇怪的介子（K介子和$ϕ$）在早期被冻结，因此可以探测反应的早期阶段。
A reheating phase in the early universe is an essential part of all inflationary models during which not only the Standard Model (SM) quanta are produced but it can also shed light on the production of dark matter. In this work, we explore a class of reheating models where the reheating is induced by a cubic interaction of the inflaton $ϕ$ to the SM Higgs boson ${\textbf h}$ of the form $g_{hϕ} M_{\rm Pl} ϕ|{\textbf h}|^2$ adopting the $α$-attractor T-model of inflation. Assuming inflaton as a background field such interaction implies a $ϕ$-dependent mass term of the Higgs boson and a non-triv…
Dark matter with strong self-interactions provides a compelling solution to several small-scale structure puzzles. Under the assumption that the coupling between dark matter and the Standard Model particles is suppressed, such strongly interacting massive particles (SIMPs) allow for a successful thermal freeze-out through N-to-N' processes, where N dark matter particles annihilate to N' of them. In the most common scenarios, where dark matter stability is guaranteed by a $\mathbb{Z}_2$ symmetry, the seemingly leading annihilating channel, i.e. 3-to-2 process, is forbidden, so the 4-to-2 one do…
Freeze-in sterile neutrino dark matter in a feebly gauged $B-L$ model
该研究在$U(1)_{B-L}$规范模型中分析惰性中微子暗物质的冻结产生机制，明确不同产生路径的作用，推导对应规范耦合常数的取值范围，并指出部分参数区间可通过对撞机实验验证。
The cosmological abundance of dark matter can be significantly influenced by the temperature dependence of particle masses and vacuum expectation values. We illustrate this point in three simple freeze-in models. The first one, which we call kinematically induced freeze-in, is based on the observation that the effective mass of a scalar temporarily becomes very small as the scalar potential undergoes a second order phase transition. This opens dark matter production channels that are otherwise forbidden. The second model we consider, dubbed vev-induced freeze-in, is a fermionic Higgs portal sc…
We investigate observable cosmological aspects of sterile neutrino dark matter produced via the freeze-in mechanism. The study is performed in a framework that admits many cosmologically interesting variations: high temperature production via annihilation processes from higher dimensional operators or low temperature production from decays of a scalar, with the decaying scalar in or out of equilibrium with the thermal bath, in supersymmetric or non-supersymmetric setups, thus allowing us to both extract generic properties and highlight features unique to particular variations. We find that whi…
We consider thermal production mechanisms of self-interacting dark matter in models with gauged $Z_3$ symmetry. A complex scalar dark matter is stabilized by the $Z_3$, that is the remnant of a local dark $U(1)_d$. Light dark matter with large self-interaction can be produced from thermal freeze-out in the presence of SM-annihilation, SIMP and/or forbidden channels. We show that dark photon and/or dark Higgs should be relatively light for unitarity and then assist the thermal freeze-out. We identify the constraints on the parameter space of dark matter self-interaction and mass in cases that o…
We study a light thermal scalar dark matter (DM) model with a light scalar mediator mixed with the standard model Higgs boson, including both the theoretical bounds and the current experimental constraints. The thermal scalar DM with the mass below a few GeV is usually strongly constrained by the observation of CMB and/or indirect detection experiments because the leading annihilation mode is S-wave. However, we find that two parameter regions still remain, which are the resonant annihilation region and the forbidden annihilation region. For the both cases, higher partial waves dominantly cont…
Exponential suppression or commonly known as the Boltzmann suppression in the number density of dark matter is the key ingredient for creating chemical imbalance prior to the usual thermal freeze-out. A degenerate/quasi-degenerate dark sector can experience a different exponential suppression in the number density analogous to the radioactive decay law leading to a delayed freeze-out mechanism of dark matter known as the co-decaying dark matter. In this work, we study the dynamics of a multicomponent dark matter from thermally decoupled degenerate dark sector in a hidden U$(1)_{X}$ extension o…
The early universe could feature multiple reheating events, leading to jumps in the visible sector entropy density that dilute both particle asymmetries and the number density of frozen-out states. In fact, late time entropy jumps are usually required in models of Affleck-Dine baryogenesis, which typically produces an initial particle-antiparticle asymmetry that is much too large. An important consequence of late time dilution, is that a smaller dark matter annihilation cross section is needed to obtain the observed dark matter relic density. For cosmologies with high scale baryogenesis, follo…
Dark Matter Annihilation via Breit-Wigner Enhancement with Heavier Mediator
提出通过 Breit-Wigner 共振增强暗物质早期冻结与黑洞附近湮灭的新场景，利用较重介子避开宇宙微波背景约束，并指出超大质量黑洞可重新激活湮灭产生光子信号，可由 Fermi-LAT 和 COSI 卫星检验。
Kination and the Inert Doublet Model
惰性双重态模型在kination宇宙学场景中允许暗物质质量窗口，解决了暗物质过量不足的问题。
Relativistic axions are good candidates for the dark radiation for which there are mounting observational hints. The primordial decays of heavy fields produce axions which are ultra-energetic compared to thermalised matter and inelastic axion-matter scattering can occur with $E_{CoM} \gg T_γ$, thus accessing many interesting processes which are otherwise kinematically forbidden in standard cosmology. Axion-photon scattering into quarks and leptons during BBN affects the light element abundances, and bounds on overproduction of $^4$He constrain a combination of the axion decay constant and the …
In this paper, we introduce a novel program of fixed-target searches for thermal-origin Dark Matter (DM), which couples inelastically to the Standard Model. Since the DM only interacts by transitioning to a heavier state, freeze-out proceeds via coannihilation and the unstable heavier state is depleted at later times. For sufficiently large mass splittings, direct detection is kinematically forbidden and indirect detection is impossible, so this scenario can only be tested with accelerators. Here we propose new searches at proton and electron beam fixed-target experiments to probe sub-GeV coan…
We examine the vector-portal inelastic dark matter (DM) model with DM mass $m_χ$ and dark photon mass $m_{A'}$, in the `forbidden dark matter' regime where $1 \lesssim m_{A'}/m_χ\lesssim 2$, carefully tracking the dark sector temperature throughout freezeout. The inelastic nature of the dark sector relaxes the stringent cosmic microwave background (CMB) and self-interaction constraints compared to symmetric DM models. We determine the CMB limits on both annihilations involving excited states and annihilation into $e^+e^-$ through initial-state-radiation of an $A'$, as well as limits on the DM …
We show that the decay of the inflaton field may be incomplete, while nevertheless successfully reheating the universe and leaving a stable remnant that accounts for the present dark matter abundance. We note, in particular, that since the mass of the inflaton decay products is field-dependent, one can construct models, endowed with an appropriate discrete symmetry, where inflaton decay is kinematically forbidden at late times and only occurs during the initial stages of field oscillations after inflation. We show that this is sufficient to ensure the transition to a radiation-dominated era an…
Chemical and Kinetic Equilibrium in Cosmology: Facts and Myths
本文厘清早期宇宙中化学平衡与动力学平衡的本质区别，通过中微子退耦、轻子生成及多种暗物质场景说明二者退耦顺序依赖具体模型，强调相空间演化是获得稳健宇宙学预言的关键。
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