Light new physics weakly coupled to the Higgs can induce a strong first-order electroweak phase transition (EWPT). Here, we argue that scenarios in which the EWPT is driven first-order by a light ...scalar with mass between ~ 10 GeV − mh /2 and small mixing with the Higgs will be conclusively probed by the high-luminosity LHC and future Higgs factories. Our arguments are based on analytic and numerical studies of the finite-temperature effective potential and provide a well-motivated target for exotic Higgs decay searches at the LHC and future lepton colliders.
Looking for the WIMP next door Evans, Jared A.; Gori, Stefania; Shelton, Jessie
The journal of high energy physics,
02/2018, Letnik:
2018, Številka:
2
Journal Article
Recenzirano
Odprti dostop
A
bstract
We comprehensively study experimental constraints and prospects for a class of minimal hidden sector dark matter (DM) models, highlighting how the cosmological history of these models ...informs the experimental signals. We study simple ‘secluded’ models, where the DM freezes out into unstable dark mediator states, and consider the minimal cosmic history of this dark sector, where coupling of the dark mediator to the SM was sufficient to keep the two sectors in thermal equilibrium at early times. In the well-motivated case where the dark mediators couple to the Standard Model (SM) via renormalizable interactions, the requirement of thermal equilibrium provides a minimal, UV-insensitive, and predictive cosmology for hidden sector dark matter. We call DM that freezes out of a dark radiation bath in thermal equilibrium with the SM a
WIMP next door
, and demonstrate that the parameter space for such WIMPs next door is sharply defined, bounded, and in large part potentially accessible. This parameter space, and the corresponding signals, depend on the leading interaction between the SM and the dark mediator; we establish it for both Higgs and vector portal interactions. In particular, there is a cosmological lower bound on the portal coupling strength necessary to thermalize the two sectors in the early universe. We determine this thermalization floor as a function of equilibration temperature for the first time. We demonstrate that direct detection experiments are currently probing this cosmological lower bound in some regions of parameter space, while indirect detection signals and terrestrial searches for the mediator cut further into the viable parameter space. We present regions of interest for both direct detection and dark mediator searches, including motivated parameter space for the direct detection of sub-GeV DM.
Decoupled hidden sectors can easily and generically result in a period of cannibal domination, during which the dominant component of the Universe has an equation of state intermediate between ...radiation and matter due to self-heating by number-changing interactions. We present for the first time the consequences of a cannibal-dominated era prior to big bang nucleosynthesis for structure formation on small scales. We find that an early cannibal-dominated era imprints a characteristic peak on the dark matter power spectrum, with scale and amplitude directly determined by the mass, lifetime, and number-changing interaction strength of the cannibal field. This enhancement to the small-scale matter power spectrum will generate early-forming dark matter microhalos, and we provide a detailed and transparent map between the properties of the cannibal species and the characteristic mass and formation time of these structures. These relations demonstrate how the internal workings of a hidden sector leave a potentially observable imprint on the matter power spectrum even if dark matter has no direct couplings to the Standard Model.
A
bstract
Rotations of an axion field in field space provide a natural origin for an era of kination domination, where the energy density is dominated by the kinetic term of the axion field, preceded ...by an early era of matter domination. Remarkably, no entropy is produced at the end of matter domination and hence these eras of matter and kination domination may occur even after Big Bang Nucleosynthesis. We derive constraints on these eras from both the cosmic microwave background and Big Bang Nucleosynthesis. We investigate how this cosmological scenario affects the spectrum of possible primordial gravitational waves and find that the spectrum features a triangular peak. We discuss how future observations of gravitational waves can probe the viable parameter space, including regions that produce axion dark matter by the kinetic misalignment mechanism or the baryon asymmetry by axiogenesis. For QCD axion dark matter produced by the kinetic misalignment mechanism, a modification to the inflationary gravitational wave spectrum occurs above 0.01 Hz and, for high values of the energy scale of inflation, the prospects for discovery are good. We briefly comment on implications for structure formation of the universe.
We introduce simplified models for enhancements in the matter power spectrum at small scales and study their implications for dark matter substructure and gravitational observables. These models ...capture the salient aspects of a variety of early Universe scenarios that predict enhanced small-scale structure, such as axionlike particle dark matter, light vector dark matter, and epochs of early matter domination. We use a model-independent, semianalytic treatment to map bumps in the matter power spectrum to early forming subsolar mass dark matter halos and estimate their evolution, disruption, and contribution to the substructure of clusters and galaxies at late times. We discuss the sensitivity of gravitational observables, including pulsar timing arrays and caustic microlensing, to both the presence of bumps in the power spectrum and variations in their basic properties.
A
bstract
Dark matter (DM) freeze-in through a light mediator is an appealing model with excellent detection prospects at current and future experiments. Light mediator freeze-in is UV-insensitive ...insofar as most DM is produced at late times, and thus the DM abundance does not depend on the unknown early evolution of our universe. However the final DM yield retains a dependence on the initial DM population, which is usually assumed to be exactly zero. We point out that in models with light mediators, the final DM yield will also depend on the initial conditions assumed for the light mediator population. We describe a class of scenarios we call “glaciation” where DM freezing in from the SM encounters a pre-existing thermal bath of mediators, and study the dependence of the final DM yield on the initial temperature of this dark radiation bath. To compute DM scattering rates in this cosmology, we derive for the first time an exact integral expression for the Boltzmann collision term describing interactions between two species at different temperatures. We quantify the dependence of the DM yield on the initial dark temperature and find that it can be sizeable in regions near the traditional (zero initial abundance) freeze-in curve. We generalize the freeze-in curve to a glaciation band, which can extend as much as an order of magnitude below the traditional freeze-in direct detection target, and point out that the DM phase space distribution as well as the yield can be strongly dependent on initial conditions.
Reheating in two-sector cosmology Adshead, Peter; Ralegankar, Pranjal; Shelton, Jessie
The journal of high energy physics,
08/2019, Letnik:
2019, Številka:
8
Journal Article
Recenzirano
Odprti dostop
A
bstract
We analyze reheating scenarios where a hidden sector is populated during reheating along with the sector containing the Standard Model. We numerically solve the Boltzmann equations ...describing perturbative reheating of the two sectors, including the full dependence on quantum statistics, and study how quantum statistical effects during reheating as well as the non-equilibrium inflaton-mediated energy transfer between the two sectors affects the temperature evolution of the two radiation baths. We obtain new power laws describing the temperature evolution of fermions and bosons when quantum statistics are important during reheating. We show that inflaton-mediated scattering is generically most important at radiation temperatures
T
∼
M
ϕ
/4, and build on this observation to obtain analytic estimates for the temperature asymmetry produced by asymmetric reheating. We find that for reheating temperatures
T
rh
≪
M
ϕ
/4, classical perturbative reheating provides an excellent approximation to the final temperature asymmetry, while for
T
rh
≫
M
ϕ
/4, inflaton-mediated scattering dominates the population of the colder sector and thus the final temperature asymmetry. We additionally present new techniques to calculate energy transfer rates between two relativistic species at different temperatures.
Leak-in dark matter Evans, Jared A.; Gaidau, Cristian; Shelton, Jessie
The journal of high energy physics,
01/2020, Letnik:
2020, Številka:
1
Journal Article
Recenzirano
Odprti dostop
A
bstract
We introduce leak-in dark matter, a novel out-of-equilibrium origin for the dark matter (DM) in the universe. We provide a comprehensive and unified discussion of a minimal, ...internally-thermalized, hidden sector populated from an out-of-equilibrium, feeble connection to the hotter standard model (SM) sector. We emphasize that when this out-of-equilibrium interaction is renormalizable, the colder sector undergoes an extended phase of non-adiabatic evolution largely independent of initial conditions, which we dub “leak-in.” We discuss the leak-in phase in generality, and establish the general properties of dark matter that freezes out from a radiation bath undergoing such a leak-in phase. As a concrete example, we consider a model where the SM has an out-of-equilibrium
B − L
vector portal interaction with a minimal hidden sector. We discuss the interplay between leak-in and freezein processes in this theory in detail and demonstrate regions where leak-in yields the full relic abundance. We study observational prospects for
B − L
vector portal leak-in DM, and find that despite the requisite small coupling to the SM, a variety of experiments can serve as sensitive probes of leak-in dark matter. Additionally, regions allowed by all current constraints yield DM with self-interactions large enough to address small-scale structure anomalies.
PDF
