Elastically Decoupling Dark Matter

Kuflik, Eric; Perelstein, Maxim; Lorier, Nicolas Rey-Le; Tsai, Yu-Dai

doi:10.1103/physrevlett.116.221302

Cited by 177 publications

(180 citation statements)

References 68 publications

(74 reference statements)

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“…[5], we assume DM begins in thermal equilibrium, has its number diluted through 2-to-2 annihilations, and has a temperature that tracks the photon temperature (for studies that relax at least one of these assumptions see for example Refs. [14][15][16][17][18][19][20][21][22][23][24][25][26][27]). We consider the presence of two states charged under the symmetry that stabilizes DM: χ and ψ, where m χ < m ψ and χ is DM.…”

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confidence: 99%

Fourth Exception in the Calculation of Relic Abundances

2017

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We propose that the dark matter abundance is set by the decoupling of inelastic scattering instead of annihilations. This coscattering mechanism is generically realized if dark matter scatters against states of comparable mass from the thermal bath. Coscattering points to dark matter that is exponentially lighter than the weak scale and has a suppressed annihilation rate, avoiding stringent constraints from indirect detection. Dark matter upscatters into states whose late decays can lead to observable distortions to the blackbody spectrum of the cosmic microwave background.Introduction: Dark Matter (DM) constitutes most of the matter in our Universe, but its origin is unknown. One of the most attractive possibilities is that DM starts in thermal equilibrium in the early Universe, and its abundance is set once its annihilations become slower than the expansion rate. This framework is insensitive to initial conditions and has the further appeal of tying the DM abundance to its (potentially observable) interactions.The most widely considered possibility is that 2-to-2 annihilations to Standard Model (SM) particles set the DM relic density. This is known as the Weakly Interacting Massive Particle (WIMP) paradigm [1-4] and points to DM particles with weak scale masses and crosssections. This theoretical framework has had considerable impact shaping experimental searches for DM.However it has long been appreciated that simple variations to the cosmology of thermal relics can have dramatic consequences. In a seminal paper, Ref.[5] enumerates three "exceptions" to thermal relic cosmology: (1) mutual annihilations of multiple species (coannihilations), (2) annihilations into heaver states (forbidden channels), and (3) annihilations near a pole in the cross section. These exceptions lead to phenomenology that can differ significantly from standard WIMPs (see for example [11][12][13]34]), while sharing their appealing theoretical features.In this letter, we introduce a fourth exception. Like Ref.[5], we assume DM begins in thermal equilibrium, has its number diluted through 2-to-2 annihilations, and has a temperature that tracks the photon temperature (for studies that relax at least one of these assumptions see for example Refs. [14][15][16][17][18][19][20][21][22][23][24][25][26][27]). We consider the presence of two states charged under the symmetry that stabilizes DM: χ and ψ, where m χ < m ψ and χ is DM. We assume that χ annihilations are suppressed, and two processes are active:

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confidence: 99%

Fourth Exception in the Calculation of Relic Abundances

2017

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“…For the example of a hidden-sector dark matter particle, χ coupled to a dark photon, A , with m A = 3m χ , we show a darker gray region that combines constraints from accelerator-based searches (LSND, E137, BaBar) and traditional nuclear recoil searches [22,23,24,25,6]. We also show several benchmark theory targets for which the dark matter can obtain the observed relic abundance [26,27,28,29,25]. Right: Here, the scattering is mediated by an ultralight particle.…”

Section: Lbeca Science Goals and Sensitivitymentioning

confidence: 75%

LBECA: A Low Background Electron Counting Apparatus for Sub-GeV Dark Matter Detection

Bernstein

Clark

Essig

et al. 2020

J. Phys.: Conf. Ser.

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Two-phase noble liquid detectors, with large target masses and effective background reduction, are currently leading the dark matter direct detection for WIMP masses above a few GeV. Due to their sensitivity to single ionized electron signals, these detectors were shown to also have strong constraints for sub-GeV dark matter via their scattering on electrons. In fact, the most stringent direct detection constraints for sub-GeV dark matter down to as low as 5 MeV come from noble liquid detectors, namely XENON10, DarkSide-50, XENON100 and XENON1T, although these experiments still suffer from high background at single or a few electron level. LBECA is a planned 100-kg scale liquid xenon detector with significant reduction of the single and a few electron background. The experiment will improve the sensitivity to sub-GeV dark matter by three orders of magnitude compared to the current best constraints.

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“…This scaling was assumed when deriving the relic density in section 2.1. If we relax the assumption that DM is in thermal contact with radiation, then the dark sector will undergo a phase of cannibalism [18,28,[68][69][70][71][72][73][74], where T dark drops only logarithmically with the scale factor. We leave the study of coannihilation in a cannibalizing sector for future work.…”

Section: Annihilations To Dark Sector Particlesmentioning

confidence: 99%

Exponentially light dark matter from coannihilation

D’Agnolo

Mondino

Wang

et al. 2018

J. High Energ. Phys.

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Dark matter may be a thermal relic whose abundance is set by mutual annihilations among multiple species. Traditionally, this coannihilation scenario has been applied to weak scale dark matter that is highly degenerate with other states. We show that coannihilation among states with split masses points to dark matter that is exponentially lighter than the weak scale, down to the keV scale. We highlight the regime where dark matter does not participate in the annihilations that dilute its number density. In this "sterile coannihilation" limit, the dark matter relic density is independent of its couplings, implying a broad parameter space of thermal relic targets for future experiments. Light dark matter from coannihilation evades stringent bounds from the cosmic microwave background, but will be tested by future direct detection, fixed target, and long-lived particle experiments.

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Elastically Decoupling Dark Matter

Cited by 177 publications

References 68 publications

Fourth Exception in the Calculation of Relic Abundances

Fourth Exception in the Calculation of Relic Abundances

LBECA: A Low Background Electron Counting Apparatus for Sub-GeV Dark Matter Detection

Exponentially light dark matter from coannihilation

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