The coannihilation codex

Baker, Michael J.; Brod, Joachim; Hedri, Sonia El; Kaminska, Anna; Liu, Jia; Thamm, Andrea; Vries, Maikel de; Wang, Xiaoping; Yu, Felix; Zurita, José

doi:10.1007/jhep12(2015)120

Cited by 86 publications

(122 citation statements)

References 178 publications

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“…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.…”

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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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“…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.…”

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confidence: 99%

Fourth Exception in the Calculation of Relic Abundances

2017

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“…However, this classification may miss an effect of co-annihilation that can be important to determine the DM relic density [50]. In the scenario where the co-annihilation is operative, a charged (or coloured) particle is introduced in addition to the DM, which we call the co-annihilation partner.…”

Section: Jhep06(2017)041mentioning

confidence: 99%

Simplified models of dark matter with a long-lived co-annihilation partner

Khoze

Plascencia

Sakurai

2017

J. High Energ. Phys.

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We introduce a new set of simplified models to address the effects of 3-point interactions between the dark matter particle, its dark co-annihilation partner, and the Standard Model degree of freedom, which we take to be the tau lepton. The contributions from dark matter co-annihilation channels are highly relevant for a determination of the correct relic abundance. We investigate these effects as well as the discovery potential for dark matter co-annihilation partners at the LHC. A small mass splitting between the dark matter and its partner is preferred by the co-annihilation mechanism and suggests that the co-annihilation partners may be long-lived (stable or meta-stable) at collider scales. It is argued that such long-lived electrically charged particles can be looked for at the LHC in searches of anomalous charged tracks. This approach and the underlying models provide an alternative/complementarity to the mono-jet and multi-jet based dark matter searches widely used in the context of simplified models with s-channel mediators. We consider four types of simplified models with different particle spins and coupling structures. Some of these models are manifestly gauge invariant and renormalizable, others would ultimately require a UV completion. These can be realised in terms of supersymmetric models in the neutralino-stau co-annihilation regime, as well as models with extra dimensions or composite models.

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“…For larger values of Δm, however, the decay of the heavier component is more rapid and can thus occur within the detection volume. Such scenarios have been considered in the context of colliders [53][54][55][56][57][58][59] as well as fixed-target experiments [60,61]. Key features of these scenarios are the detection of Standard-Model particles arising from the decay of the heavier dark particle, potentially with a displaced vertex.…”

Section: Collider Constraintsmentioning

confidence: 99%

Off-diagonal dark-matter phenomenology: Exploring enhanced complementarity relations in nonminimal dark sectors

2017

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In most multicomponent dark-matter scenarios, two classes of processes generically contribute to event rates at experiments capable of probing the nature of the dark sector. The first class consists of "diagonal" processes involving only a single species of dark-matter particle-processes analogous to those which arise in single-component dark-matter scenarios. By contrast, the second class consists of "off-diagonal" processes involving dark-matter particles of different species. Such processes include inelastic scattering at direct-detection experiments, asymmetric production at colliders, dark-matter co-annihilation, and certain kinds of dark-matter decay. In typical multicomponent scenarios, the contributions from diagonal processes dominate over those from off-diagonal processes. Unfortunately, this tends to mask those features which are most sensitive to the multicomponent nature of the dark sector. In this paper, by contrast, we point out that there exist natural, multicomponent dark-sector scenarios in which the off-diagonal contributions actually dominate over the diagonal. This then gives rise to a new, enhanced picture of dark-matter complementarity. In this paper, we introduce a scenario in which this situation arises and examine the enhanced picture of dark-matter complementarity which emerges.

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The coannihilation codex

Cited by 86 publications

References 178 publications

Fourth Exception in the Calculation of Relic Abundances

Fourth Exception in the Calculation of Relic Abundances

Simplified models of dark matter with a long-lived co-annihilation partner

Off-diagonal dark-matter phenomenology: Exploring enhanced complementarity relations in nonminimal dark sectors

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