The neutrino minimal Standard Model (νMSM) is the minimum extension of the standard model. In this model, the Dodelson-Widrow mechanism (DW) produces keV sterile neutrino dark matter (DM) and the degenerate GeV heavy Majorana neutrinos lead to leptogenesis. However, the DW mechanism has been ruled out by Lyman-α bounds and X-ray constraints. An alternative scenario that evades these constraints has been proposed, where the sterile neutrino DM is generated by the thermal freeze-in mechanism via a singlet scalar. In this paper, we consider a Higgs sector extension of the νMSM to improve dark matter sectors and leptogenesis scenarios, focusing on the thermal freeze-in production mechanism. We discuss various thermal freeze-in scenarios for the production of keV-MeV sterile neutrino DM with a singlet scalar, and reinvestigate the Lyman-α bounds and the X-ray constraints on the parameter regions. Furthermore, we propose thermal freeze-in leptogenesis scenarios in the extended νMSM. The singlet scalar needs to be TeV scale in order to generate the observed DM relic density and baryon number density with the thermal freeze-in production mechanism.
The clockwork mechanism allows extremely weak interactions and small mass scales to be understood in terms of the structure of a theory. A natural application of the clockwork mechanism is to the freeze-in mechanism for dark matter production. Here we consider a Higgs portal freeze-in dark matter model based on a scalar clockwork sector with a mass scale which is less than the Higgs boson mass. The dark matter scalar is the lightest scalar of the clockwork sector. Freeze-in dark matter is produced by the decay of thermal Higgs bosons to the clockwork dark matter scalars. We show that the mass …
We investigate a simplified freeze-in dark-matter model in which the dark matter only interacts with the standard-model neutrinos via a light scalar. The extremely small coupling for the freeze-in mechanism is naturally realized in several neutrino-portal scenarios with the secret neutrino interactions. We study possible evolution history of the dark sector: the dark sector would undergo pure freeze-in production if the interactions between the dark-sector particles are negligible, while thermal equilibrium within the dark sector could occur if the reannihilation of the dark matter and the sca…
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 …
The clockwork mechanism can explain interactions which are dimensionally very weak without the need for very large mass scales. We present a model in which the clockwork mechanism generates the very small Higgs portal coupling and dark matter particle mass necessary to explain cold dark matter via the freeze-in mechanism. We introduce a TeV-scale scalar clockwork sector which couples to the Standard Model via the Higgs portal. The dark matter particle is the lightest scalar of the clockwork sector. We show that the freeze-in mechanism is dominated by decay of the heavy clockwork scalars to lig…
The dark glueball (DGB) from a hidden Yang-Mills sector is a simple non-WIMP dark matter candidate characterized by very few parameters. However, it suffers the over dense issue. To overcome it, in general the dark sector is required to be hierarchically cooler than the visible sector. To naturally generate the desired hierarchy, in this paper we introduce higher dimensional operators coupling the dark gauge field strength tensor to the standard model (SM) Higgs doublets or gauge field strength tensors. By tracking the different phases of the universe from the end of inflation, prethermalizati…
Warm dark matter (WDM) of order keV mass may be able to resolve the disagreement between structure formation in cold dark matter simulations and observations. The detailed properties of WDM will depend upon its energy distribution, in particular how it deviates from the thermal distribution usually assumed in WDM simulations. Here we focus on WDM production via the Ultra-Violet (UV) freeze-in mechanism, for the case of fermionic Higgs portal dark matter $ψ$ produced via the portal interaction $\barψψH^{\dagger}H/Λ$. We introduce a new method to simplify the computation of the non-thermal energ…
We study a vector dark matter (VDM) model in which the dark sector couples to the Standard Model sector via a Higgs portal. If the portal coupling is small enough the VDM can be produced via the freeze-in mechanism. It turns out that the electroweak phase transition have a substantial impact on the prediction of the VDM relic density. We further assume that the dark Higgs boson which gives the VDM mass is so light that it can induce strong VDM self-interactions and solve the small-scale structure problems of the Universe. As illustrated by the latest LUX data, the extreme smallness of the Higg…
We present an interesting Higgs portal model where an axion-like particle (ALP) couples to the Standard Model sector only via the Higgs field. The ALP becomes stable due to CP invariance and turns out to be a natural candidate for freeze-in dark matter because its properties are controlled by the perturbative ALP shift symmetry. The portal coupling can be generated non-perturbatively by a hidden confining gauge sector, or radiatively by new leptons charged under the ALP shift symmetry. Such UV completions generally involve a CP violating phase, which makes the ALP unstable and decay through mi…
We study the possibility that, after inflation, the inflaton reaches thermal equilibrium with the Standard Model thermal bath and eventually freezes-out in the non-relativistic regime. When the inflaton decay is the sole source of (non-thermal) dark matter, its relic density is automatically suppressed. We delineate parameter space leading to the correct dark matter abundance. The model allows for a significant Higgs-inflaton coupling which may lead to invisible Higgs decay into inflaton pairs at the LHC.
We explore relativistic freeze-in production of scalar dark matter in gauged $B-L$ model, where we focus on the production of dark matter from the decay and annihilation of Standard Model (SM) and $B-L$ Higgs bosons. We consider the Bose-Einstein (BE) and Fermi-Dirac (FD) statistics, along with the thermal mass correction of the SM Higgs boson in our analysis. We show that in addition to the SM Higgs boson, the annihilation and decay of the $B-L$ scalar can also contribute substantially to the dark matter relic density. Potential effects of electroweak symmetry breaking (EWSB) and thermal mass…
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…
We study production of scalar dark matter via the freeze--in mechanism in the relativistic regime, focussing on the simplest Higgs portal model. We derive the corresponding relativistic reaction rates based on the Bose--Einstein statistics taking into account the thermal mass effects as well as the change in the Higgs degrees of freedom at the electroweak phase transition. The consequent constraints on the Higgs portal coupling are obtained.
We propose a new mechanism where a multi-component dark sector generates the observed dark matter abundance and baryon asymmetry and thus addresses the coincidence between the two. The thermal freeze-out of dark matter annihilating into meta-stable dark partners sets the dark matter relic abundance while providing the out-of-equilibrium condition for baryogenesis. The meta-stable state triggers baryon asymmetry production by its decay well after the freeze-out and potentially induces a period of early matter domination before its decay. The dark matter and baryon abundances are related through…
Precision cosmology provides a sensitive probe of extremely weakly coupled states due to thermal freeze-in production, with subsequent decays impacting physics during well-tested cosmological epochs. We explore the cosmological implications of the freeze-in production of a new scalar $S$ via the super-renormalizable Higgs portal. If the mass of $S$ is at or below the electroweak scale, peak freeze-in production occurs during the electroweak epoch. We improve the calculation of the freeze-in abundance by including all relevant QCD and electroweak production channels. The resulting abundance and…
We explore the dark matter freeze-in mechanism within the gauge mediation framework, which involves a hidden Feebly Interacting Massive Particle (FIMP) coupling feebly with the messenger fields while the messengers are still in the thermal bath. The FIMP is the fermionic component of the pseudo-moduli in a generic metastable supersymmetry (SUSY) breaking model and resides in the hidden sector. The relic abundance and the mass of the FIMP are determined by the SUSY breaking scale and the feeble coupling. The gravitino, which is the canonical dark matter candidate in the gauge mediation framewor…
This paper considers unitarity and CPT constraints on asymmetric freeze-in, the use of freeze-in to store baryon number in a dark sector. In this scenario, Sakharov's out of equilibrium condition is satisfied by placing the visible and hidden sectors at different temperatures while a net visible baryon number is produced by storing negative baryon number in a dark sector. It is shown that unitarity and CPT lead to unexpected cancellations. In particular, the transfer of baryon number cancels completely at leading order.
In extended supersymmetric models with a hidden sector the lightest $R$-parity odd particle can reside in the hidden sector and act as dark matter. We consider the case when the hidden sector has ultraweak interactions with the visible sector. An interesting phenomenon arises if the LSP of the visible sector is charged in which case it will decay to the hidden sector dark matter. Due to the ultraweak interactions, the LSP of the visible sector will be long-lived decaying outside the detector after leaving a track inside. We investigate this possibility in the framework of a $U(1)_X$-extended M…
Sterile neutrinos at the GeV scale can resolve several outstanding problems of the Standard Model (SM), such as the source of neutrino masses and the origin of the baryon asymmetry through freeze-in leptogenesis, but they can be challenging to detect experimentally due to their small couplings to SM particles. In extensions of the SM with new interactions of the sterile neutrinos, they can be produced copiously at accelerators and colliders. We systematically investigate the impact of such novel interactions on the asymmetry from freeze-in leptogenesis. We find that the interactions tend to br…
If dark matter is thermally decoupled from the visible sector, the observed relic density can potentially be obtained via freeze-in production of dark matter. Typically in such models it is assumed that the dark matter is connected to the thermal bath through feeble renormalisable interactions. Here, rather, we consider the case in which the hidden and visible sectors are coupled only via non-renormalisable operators. This is arguably a more generic realisation of the dark matter freeze-in scenario, as it does not require the introduction of diminutive renormalisable couplings. We examine gene…
We study the post-inflationary dynamics for reheating and freeze-in dark matter in the Higgs-$R^2$ inflation model. Taking the perturbative approach for reheating, we determine the evolution of the temperature for radiation bath produced during reheating and determine the maximum and reheating temperatures of the Universe. Adopting a singlet scalar dark matter with a conformal non-minimal coupling and a vanishing Higgs-portal coupling, we discuss the freeze-in production of dark matter both from the non-thermal scattering during reheating and the thermal scattering after reheating. We find tha…
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 introduce a novel mechanism where processes that preserve the number density of the dark sector set the relic density of a thermal particulate dark matter. In a relatively degenerate multipartite dark sector if there is a considerable time lapse between the freeze out of various species then a process like exchange between dark sector constituents can play the pivotal role of driving freeze out and setting dark matter relic density. As a proof of principle, we present simple scalar models with viable dark matter in the GeV scale to demonstrate this phenomenon.
We discuss Dirac neutrinos whose right-handed component $ν_R$ has new interactions that may lead to a measurable contribution to the effective number of relativistic neutrino species $N_{\rm eff}$. We aim at a model-independent and comprehensive study on a variety of possibilities. Processes for $ν_R$-genesis from decay or scattering of thermal species, with spin-0, spin-1/2, or spin-1 initial or final states are all covered. We calculate numerically and analytically the contribution of $ν_R$ to $N_{\rm eff}$ primarily in the freeze-in regime, since the freeze-out regime has been studied befor…
Dark matter (DM) that interacts too weakly with the Standard Model (SM) to reach full thermodynamic equilibrium can be still be created in significant amounts by rare SM collisions. This mechanism, called freeze-in, can proceed through a renormalizable connector operator with a very small coefficient, or a non-renormalizable connector operator suppressed by a large mass scale. In the latter non-renormalizable scenario, the dominant creation of DM particles typically occurs at the largest SM temperature attained during the radiation era (assuming a standard cosmological history), and for this r…
We study a simple dark matter model given by two interacting real singlet scalars, with only one of them coupled to the Higgs. The model therefore presents a minimal assisted-freeze-out framework: both scalars contribute to the dark matter relic density, but only one of them takes part in the elastic scattering with nuclei. This reduces the expected interaction rate in direct detection experiments in such a way that the model in some regions of the parameter space may evade XENON1T constraints. We explore the model under theoretical (perturbativity, stability potential and unitarity) and exper…
Motivated by the fact that the origin of tiny Dirac neutrino masses via the standard model Higgs field and non-thermal dark matter populating the Universe via freeze-in mechanism require tiny dimensionless couplings of similar order of magnitudes $(\sim 10^{-12})$, we propose a framework that can dynamically generate such couplings in a unified manner. Adopting a flavour symmetric approach based on $A_4$ group, we construct a model where Dirac neutrino coupling to the standard model Higgs and dark matter coupling to its mother particle occur at dimension six level involving the same flavon fie…
Dark Matter (DM) may belong to a hidden sector that is only feebly interacting with the Standard Model (SM) and may have never been in thermal equilibrium in the Early Universe. In this case, the observed abundance of dark matter particles could have built up through a process known as Freeze-in. We show that, for the first time, direct detection experiments are testing this DM production mechanism. This applies to scenarios where the SM and hidden sectors communicate through a light mediator particle of mass less than a few MeV. Through the exchange of such light mediator, the very same FIMP …
We consider the possibility that along the thermal history of the Universe, dark matter (DM) would have been created from Standard Model particles, either through a kinetic mixing portal to an extra U(1) gauge field, or through the Higgs portal. Depending solely on the DM particle mass, on the portal and on the DM hidden sector interaction, we show how the observed DM relic density can be obtained. There are four possible freeze-in/reannihilation/freeze-out regimes, which together result in a simple characteristic relic density phase diagram, with the shape of a "Mesa". In the case of the kine…
In models of freeze-in the dark matter (DM) is decoupled from the visible sector and initially has a depleted number density. The hidden and visible sectors are connected only via a feeble portal interaction by which DM can be produced. Asymmetric freeze-in (AFI) combines this scenario with ideas from asymmetric DM and provides a potential cogenesis mechanism. However, it has been argued that existing AFI models do not produce suitably large particle asymmetries due to cancellations which arises because the mediator state remains in thermal equilibrium. We examine AFI via an out-of-equilibrium…
WIMP-like Dark Matter Without Thermalization At Freeze-Out
University of Wisconsin, Madison（威斯康星大学麦迪逊分校）；Wisconsin IceCube Particle Astrophysics Center (WIPAC), University of Wisconsin, Madison（威斯康星冰立方粒子天体物理中心，威斯康星大学麦迪逊分校）；Fermi National Accelerator Laboratory（费米国家加速器实验室）；Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学卡弗里宇宙物理学研究所）；Department of Astronomy and Astrophysics, University of Chicago（芝加哥大学天文与天体物理系）；Texas Center for Cosmology and Astroparticle Physics, Weinberg Institute for Theoretical Physics, Department of Physics, The University of Texas at Austin（德克萨斯大学奥斯汀分校物理系温伯格理论物理研究所宇宙线与高能天体物理中心）
We use the framework of relativistic and non-relativistic conformal field theories (CFT) to derive general results relevant for the production of weakly coupled and strongly coupled dark sectors through thermal interactions. Our result reproduce trivially known formulas for $2\to n $ processes and extend to general $m\to n$ processes as well as interacting dark sectors. As concrete examples we consider freeze-in of a relativistic CFT coupled to the SM with contact interactions and derive Sommerfeld enhancement of non-relativistic cross-sections from the theory of fermions at unitarity.
Inspired by the decaying dark matter (DM) which can explain cosmic ray anomalies naturally, we consider the supersymmetric Standard Model with three right-handed neutrinos (RHNs) and R-parity, and introduce a TeV-scale DM sector with two fields ϕ_{1,2} and a $Z_3$ discrete symmetry. The DM sector only interacts with the RHNs via a very heavy field exchange and then we can explain the cosmic ray anomalies. With the second right-handed neutrino N_2 dominant seesaw mechanism at the low scale around 10^4 GeV, we show that ϕ_{1,2} can obtain the vacuum expectation values around the TeV scale, and t…
The standard model Higgs quartic coupling vanishes at $(10^{9}-10^{13})$ GeV. We study $SU(2)_L \times SU(2)_R \times U(1)_{B-L}$ theories that incorporate the Higgs Parity mechanism, where this becomes the scale of Left-Right symmetry breaking, $v_R$. Furthermore, these theories solve the strong CP problem and predict three right-handed neutrinos. We introduce cosmologies where $SU(2)_R \times U(1)_{B-L}$ gauge interactions produce right-handed neutrinos via the freeze-out or freeze-in mechanisms. In both cases, we find the parameter space where the lightest right-handed neutrino is dark matt…
Probing displaced (dark)photons from low reheating freeze-in at the LHC
Facultad de Ingeniería, Universidad San Sebastián（塞巴斯蒂安大学工程学院）；Millennium Institute for Subatomic Physics at the High-Energy Frontier (SAPHIR)（高能前沿亚原子物理千年研究所（SAPHIR））；Instituto de Física, Pontificia Universidad Católica de Chile（智利天主教大学物理研究所）；Instituto de Física, Facultad de Ciencias, Universidad de la República（共和国大学理学院物理研究所）；Sección Física, Departamento de Ciencias, Pontificia Universidad Católica del Perú（秘鲁天主教大学科学院物理组）
We propose a unified theory of dark matter (DM) genesis and baryogenesis. It explains the observed link between the DM density and the baryon density, and is fully testable by a combination of collider experiments and precision tests. Our theory utilises the "thermal freeze-in" mechanism of DM production, generating particle anti-particle asymmetries in decays from visible to hidden sectors. Calculable, linked, asymmetries in baryon number and DM number are produced by the feeble interaction mediating between the two sectors, while the out-of-equilibrium condition necessary for baryogenesis is…
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 consider an extension of the Standard Model with a singlet sector consisting of a real (pseudo)scalar and a Dirac fermion coupled with the Standard Model only via the scalar portal. We assume that the portal coupling is weak enough for the singlet sector not to thermalize with the Standard Model allowing the production of singlet particles via the freeze-in mechanism. If the singlet sector interacts with itself sufficiently strongly, it may thermalize within itself, resulting in dark matter abundance determined by the freeze-out mechanism operating within the singlet sector. We investigate …
We present the conformal freeze-in (COFI) scenario for dark matter production. At high energies, the dark sector is described by a gauge theory flowing towards a Banks-Zaks fixed point, coupled to the standard model via a non-renormalizable portal interaction. At the time when the dark sector is populated in the early universe, it is described by a strongly coupled conformal field theory. As the universe cools, cosmological phase transitions in the standard model sector, either electroweak or QCD, induce conformal symmetry breaking and confinement in the dark sector. One of the resulting dark …
Large classes of dark sector models feature mass scales and couplings very different from the ones we observe in the Standard Model (SM). Moreover, in the freeze-in mechanism, often employed by the dark sector models, it is also required that the dark sector cannot be populated during the reheating process like the SM. This is the so called asymmetric reheating. Such disparities in sizes and scales often call for dynamical explanations. In this paper, we explore a scenario in which slow evolving conformal field theories (CFTs) offer such an explanation. Building on the recent work on conformal…
Warm dark matter from freeze-in at stronger coupling
Department of Physics and Helsinki Institute of Physics, Gustaf Hällströmin katu 2a, FI-00014 Helsinki, Finland（赫尔辛基大学物理系与赫尔辛基物理研究所）；Departamento de Física da Universidade de Aveiro and Center for Research and Development in Mathematics and Applications (CIDMA), Campus de Santiago, 3810-183 Aveiro, Portugal（阿威罗大学物理系与应用数学研发中心）；Department of Physics, Lund University, SE-223 62 Lund, Sweden（隆德大学物理系）；Laboratório de Instrumentação e Física Experimental de Partículas (LIP), Universidade do Minho, 4710-057 Braga, Portugal（米尼奥大学粒子物理实验仪器实验室）
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…
Genesis of baryon and dark matter asymmetries through ultraviolet scattering freeze-in
Institute for Fundamental Science and Department of Physics, University of Oregon（俄勒冈大学基础物理研究所与物理系）；Center for Theoretical Physics – a Leinweber Institute, Massachusetts Institute of Technology（麻省理工学院莱因韦伯理论物理中心）；Department of Physics, Harvard University（哈佛大学物理系）；TRIUMF（特里尔姆夫国家粒子加速器中心）；Department of Physics and Astronomy, University of California, Riverside（加州大学河滨分校物理与天文系）
Using a mechanism which allows naturally small Dirac neutrino masses and its linkage to a dark gauge $U(1)_D$ symmetry, a realistic Dirac neutrino mass matrix is derived from $S_3$. The dark sector naturally contains a fermion singlet having a small seesaw mass. It is thus a good candidate for freeze-in dark matter from the decay of the $U(1)_D$ Higgs boson.
In this thesis, we discuss theoretical properties of various Higgs sectors, and we analyze constraints from current experimental data, and then we study collider signatures in each Higgs sector. In Part I, we focus on the phenomenology of various extended Higgs sectors such as the two Higgs doublet model, the Higgs triplet model and Higgs sectors in supersymmetric standard models. In Part II, we discuss new physics models at the TeV scale, in which the Higgs sector is extended, and neutrino masses, dark matter and/or baryon asymmetry of the Universe can be explained.
