Asymmetric dark matter from semi-annihilation

Physical Review D, 2015

The relic abundance of particle and antiparticle dark matter (DM) need not be vastly different in thermal asymmetric dark matter (ADM) models. By considering the effect of a primordial asymmetry on the thermal Boltzmann evolution of coupled DM and anti-DM, we derive the requisite annihilation cross section. This is used in conjunction with CMB and Fermi-LAT gamma-ray data to impose a limit on the number density of anti-DM particles surviving thermal freeze-out. When the extended gamma-ray emission from the Galactic Center is reanalyzed in a thermal ADM framework, we find that annihilation into τ leptons prefer anti-DM number densities 1-4% that of DM while the b-quark channel prefers 50-100%.

Physical Review D, 2009

We consider a simple class of models in which the relic density of dark matter is determined by the baryon asymmetry of the universe. In these models a B −L asymmetry generated at high temperatures is transfered to the dark matter, which is charged under B − L. The interactions that transfer the asymmetry decouple at temperatures above the dark matter mass, freezing in a dark matter asymmetry of order the baryon asymmetry. This explains the observed relation between the baryon and dark matter densities for dark matter mass in the range 5-15 GeV. The symmetric component of the dark matter can annihilate efficiently to light pseudoscalar Higgs particles a, or via t-channel exchange of new scalar doublets. The first possibility allows for h 0 → aa decays, while the second predicts a light charged Higgs-like scalar decaying to τ ν. Direct detection can arise from Higgs exchange in the first model, or a nonzero magnetic moment in the second. In supersymmetric models, the would-be LSP can decay into pairs of dark matter particles plus standard model particles, possibly with displaced vertices.

Journal of Cosmology and Astroparticle Physics, 2012

Asymmetric Dark Matter (ADM) models invoke a particle-antiparticle asymmetry, similar to the one observed in the Baryon sector, to account for the Dark Matter (DM) abundance. Both asymmetries are usually generated by the same mechanism and generally related, thus predicting DM masses around 5 GeV in order to obtain the correct density. The main challenge for successful models is to ensure efficient annihilation of the thermally produced symmetric component of such a light DM candidate without violating constraints from collider or direct searches. A common way to overcome this involves a light mediator, into which DM can efficiently annihilate and which subsequently decays into Standard Model particles. Here we explore the scenario where the light mediator decays instead into lighter degrees of freedom in the dark sector that act as radiation in the early Universe. While this assumption makes indirect DM searches challenging, it leads to signals of extra radiation at BBN and CMB. Under certain conditions, precise measurements of the number of relativistic species, such as those expected from the Planck satellite, can provide information on the structure of the dark sector. We also discuss the constraints of the interactions between DM and Dark Radiation from their imprint in the matter power spectrum.

2014

We consider flavor constraints on, and collider signatures of, asymmetric dark matter (ADM) via higher dimension operators. In the supersymmetric models we consider, $R$-parity-violating (RPV) operators carrying $B\ensuremath{-}L$ interact with $n$ dark matter particles $X$ through an interaction of the form $W={X}^{n}{\mathcal{O}}_{B\ensuremath{-}L}$, where ${\mathcal{O}}_{B\ensuremath{-}L}=q\ensuremath{\ell}{d}^{c}$, ${u}^{c}{d}^{c}{d}^{c}$, $\ensuremath{\ell}\ensuremath{\ell}{e}^{c}$. This interaction ensures that the lightest ordinary supersymmetric particle is unstable to decay into the $X$ sector, leading to a higher multiplicity of final state particles and reduced missing energy at a collider. Flavor-violating processes place constraints on the scale of the higher dimension operator, impacting whether the LOSP decays promptly. While the strongest limitations on RPV from $n\ensuremath{-}\overline{n}$ oscillations and proton decay do not apply to ADM, we analyze the constraint...

The European Physical Journal C, 2021

We point out qualitatively different possibilities on the role of CP-conserving processes in generating cosmological particle–antiparticle asymmetries, with illustrative examples from models in leptogenesis and asymmetric dark matter production. In particular, we consider scenarios in which the CP-violating and CP-conserving processes are either both decays or both scatterings, thereby being naturally of comparable rates. This is in contrast to the previously considered CP-conserving processes in models of leptogenesis in different see-saw mechanisms, in which the CP-conserving scatterings typically have lower rates compared to the CP-violating decays, due to a Boltzmann suppression. We further point out that the CP-conserving processes can play a dual role if the asymmetry is generated in the mother sector itself, in contrast to the conventional scenarios in which it is generated in the daughter sector. This is because, the CP-conserving processes initially suppress the asymmetry g...

Journal of High Energy Physics, 2012

Supersymmetric extensions to the standard model provide viable dark matter candidates and can introduce additional charge-parity (CP) violation needed for obtaining the observed baryon asymmetry of the universe. We study the possibilities of scalar and neutralino dark matter with spontaneous CP violation in the next-to-minimal supersymmetric standard model with a right-handed neutrino. The observed relic density can be produced both by a neutralino or a right-handed sneutrino as the lightest supersymmetric particle but when CP is violated new annihilation channels become available and in general lower the relic density. We consider collider phenomenology for a number of benchmark points which all satisfy experimental constraints and have either the neutralino or the right-handed sneutrino contribute to the dark matter abundance.

Journal of Cosmology and Astroparticle Physics, 2015

We explore possible asymmetric dark matter models using CP violating scatterings to generate an asymmetry. In particular, we introduce a new model, based on DM fields coupling to the SM Higgs and lepton doublets, a neutrino portal, and explore its UV completions. We study the CP violation and asymmetry formation of this model, to demonstrate that it is capable of producing the correct abundance of dark matter and the observed matter-antimatter asymmetry. Crucial to achieving this is the introduction of interactions which violate CP with a T 2 dependence.

Journal of Cosmology and Astroparticle Physics, 2010

We discuss possible signatures of Asymmetric Dark Matter (ADM) through dark matter decays to neutrinos. We specifically focus on scenarios in which the Standard Model (SM) baryon asymmetry is transferred to the dark sector (DS) through higher dimensional operators in chemical equilibrium. In such cases, the dark matter (DM) carries lepton and/or baryon number, and we point out that for a wide range of quantum number assignments, by far the strongest constraints on dark matter decays come from decays to neutrinos through the "neutrino portal" operator HL. Together with the facts that ADM favors lighter DM masses ∼ a few GeV and that the decays would lead only to anti-neutrinos and no neutrinos (or vice versa), the detection of such decays at neutrino telescopes would provide compelling evidence for ADM. We discuss current and future bounds on models where the DM decays to neutrinos through operators of dimension ≤ 6. For dimension 6 operators, the scale suppressing the decay is bounded to be 10 12 − 10 13 GeV.

2010

Cold dark matter particles with an intrinsic matter-antimatter asymmetry do not annihilate after gravitational capture by the Sun and can affect its interior structure. The rate of capture is exponentially enhanced when such particles have self-interactions of the right order to explain structure formation on galactic scales. A 'dark baryon' of mass 5 GeV is a natural candidate and has the required relic abundance if its asymmetry is similar to that of ordinary baryons. We show that such particles can solve the 'solar composition problem'. The predicted small decrease in the low energy neutrino fluxes may be measurable by the Borexino and SNO+ experiments.

2012

The dark matter content of the Universe is likely to be a mixture of matter and antimatter, perhaps comparable to the measured asymmetric mixture of baryons and antibaryons. During the early stages of the Universe, the dark matter particles are produced in a process similar to baryogenesis, and dark matter freeze-out depends on the dark matter asymmetry and the annihilation cross section (s-wave and p-wave annihilation channels) of particles and antiparticles. In these η−parametrised asymmetric dark matter models (ηADM), the dark matter particles have an annihilation cross section close to the weak interaction cross section, and a value of dark matter asymmetry η close to the baryon asymmetry η B . Furthermore, we assume that dark matter scattering of baryons, namely, the spin-independent scattering cross section, is of the same order as the range of values suggested by several theoretical particle physics models used to explain the current unexplained events reported in the DAMA/LIBRA, CoGeNT and CRESST experiments. Here, we constrain η−parametrised asymmetric dark matter by investigating the impact of such a type of dark matter on the evolution of the Sun, namely, the flux of solar neutrinos and helioseismology. We find that dark matter particles with a mass smaller than 15 GeV, a spin-independent scattering cross section on baryons of the order of a picobarn, and an η−asymmetry with a value in the interval 10 −12 − 10 −10 , would induce a change in solar neutrino fluxes in disagreement with current neutrino flux measurements. This result is also confirmed by helioseismology data. A natural consequence of this model is suppressed annihilation, thereby reducing the tension between indirect and direct dark matter detection experiments, but the model also allows a greatly enhanced annihilation cross section. All the cosmological η−asymmetric dark matter scenarios that we discuss have a relic dark matter density Ωh 2 and baryon asymmetry η B in agreement with the current WMAP measured values, Ω DM h 2 = 0.1109 ± 0.0056 and η B = 0.88 × 10 −10 .