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Register a new userScalar Dark Matter Candidates -- Revisited
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We revisit the possibility of light scalar dark matter, in the MeV to GeV mass bracket and coupled to electrons through fermion or vector mediators, in light of significant experimental and observational advances that probe new physics below the GeV-scale. We establish new limits from electron colliders and fixed-target beams, and derive the strength of loop-induced processes that are probed by precision physics, among other laboratory probes. In addition, we compute the cooling bound from SN1987A, consider self-scattering, structure formation, and cosmological constraints as well as the limits from dark matter-electron scattering in direct detection experiments. We then show that the combination of constraints largely excludes the possibility that the galactic annihilation of these particles may explain the long-standing INTEGRAL excess of 511 keV photons as observed in the galactic bulge. As caveat to these conclusions we identify the resonant annihilation regime where the vector mediator goes nearly on-shell.
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We perform a systematic study of the phenomenology associated to models where the dark matter consists in the neutral component of a scalar SU(2)_L n-uplet, up to n=7. If one includes only the pure gauge induced annihilation cross-sections it is known that such particles provide good dark matter candidates, leading to the observed dark matter relic abundance for a particular value of their mass around the TeV scale. We show that these values actually become ranges of values -which we determine- if one takes into account the annihilations induced by the various scalar couplings appearing in these models. This leads to predictions for both direct and indirect detection signatures as a function of the dark matter mass within these ranges. Both can be largely enhanced by the quartic coupling contributions. We also explain how, if one adds right-handed neutrinos to the scalar doublet case, the results of this analysis allow to have altogether a viable dark matter candidate, successful generation of neutrino masses, and leptogenesis in a particularly minimal way with all new physics at the TeV scale.
It is an intriguing possibility that dark matter (DM) could have flavor quantum numbers like the quarks. We propose and investigate a class of UV-complete models of this kind, in which the dark matter is in a scalar triplet of an SU(3) flavor symmetry, and interacts with quarks via a colored flavor-singlet fermionic mediator. Such mediators could be discovered at the LHC if their masses are $sim 1$ TeV. We constrain the DM-mediator couplings using relic abundance, direct detection, and flavor-changing neutral-current considerations. We find that, for reasonable values of its couplings, scalar flavored DM can contribute significantly to the real and imaginary parts of the $B_s$-$bar B_s$ mixing amplitude. We further assess the potential for such models to explain the galactic center GeV gamma-ray excess.
We consider a composite model where both the Higgs and a complex scalar $chi$, which is the dark matter (DM) candidate, arise as light pseudo Nambu-Goldstone bosons (pNGBs) from a strongly coupled sector with TeV scale confinement. The global symmetry structure is $SO(7)/SO(6)$, and the DM is charged under an exact $U(1)_{rm DM} subset SO(6)$ that ensures its stability. Depending on whether the $chi$ shift symmetry is respected or broken by the coupling of the top quark to the strong sector, the DM can be much lighter than the Higgs or have a weak-scale mass. Here we focus primarily on the latter possibility. We introduce the lowest-lying composite resonances and impose calculability of the scalar potential via generalized Weinberg sum rules. Compared to previous analyses of pNGB DM, the computation of the relic density is improved by fully accounting for the effects of the fermionic top partners. This plays a crucial role in relaxing the tension with the current DM direct detection constraints. The spectrum of resonances contains exotic top partners charged under the $U(1)_{rm DM}$, whose LHC phenomenology is analyzed. We identify a region of parameters with $f = 1.4; mathrm{TeV}$ and $200;mathrm{GeV} lesssim m_chi lesssim 400;mathrm{GeV}$ that satisfies all existing bounds. This DM candidate will be tested by XENON1T in the near future.
Dark matter made from non-thermally produced bosons can have very low, possibly sub-eV masses. Axions and hidden photons are prominent examples of such dark very weakly interacting light (slim) particles (WISPs). A suitable mechanism for their non-thermal production is the misalignment mechanism. Their dominant interaction with Standard Model (SM) particles is via photons. In this note we want to go beyond these standard examples and discuss a wide range of scalar and pseudo-scalar bosons interacting with SM matter fermions via derivative interactions. Suitably light candidates arise naturally as pseudo-Nambu-Goldstone bosons. In particular we are interested in examples, inspired by familons, whose interactions have a non-trivial flavor structure.
We point out the possibility to test the simplest scalar dark matter model at gamma-ray telescopes. We discuss the relevant constraints and show the predictions for direct detection, gamma line searches and LHC searches. Since the final state radiation processes are suppressed by small Yukawa couplings one could observe the gamma lines from dark matter annihilation.
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