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Register a new userScalar Multiplet Dark Matter in a Fast Expanding Universe: resurrection of the desert region
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We examine the impact of a faster expanding Universe on the phenomenology of scalar dark matter (DM) associated with $SU(2)_L$ multiplets. Earlier works with radiation dominated Universe have reported the presence of desert region for both inert $SU(2)_L$ doublet and triplet DM candidates where the DM is under abundant. We find that the existence of a faster expanding component before BBN can revive a substantial part of the desert parameter space consistent with relic density requirements and other direct and indirect search bounds. We also review the possible collider search prospects of the newly obtained parameter space and predict that such region might be probed at the future colliders with improved sensitivity via a disappearing/stable charged track.
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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.
We revisit the theory and phenomenology of scalar electroweak multiplet thermal dark matter. We derive the most general, renormalizable scalar potential, assuming the presence of the Standard Model Higgs doublet, $H$, and an electroweak multiplet $Phi$ of arbitrary SU(2$)_L$ rank and hypercharge, $Y$. We show that, in general, the $Phi$-$H$ Higgs portal interactions depend on three, rather than two independent couplings as has been previously considered in the literature. For the phenomenologically viable case of $Y=0$ multiplets, we focus on the septuplet and quintuplet cases, and consider the interplay of relic density and spin-independent direct detection cross section. We show that both the relic density and direct detection cross sections depend on a single linear combination of Higgs portal couplings, $lambda_{rm eff}$. For $lambda_{rm eff}sim mathcal{O}(1)$, present direct detection exclusion limits imply that the neutral component of a scalar electroweak multiplet would comprise a subdominant fraction of the observed DM relic density.
We study a simplest viable dark matter model with a real singlet scalar, vector-like singlet and a doublet lepton. We find a considerable enhancement in the allowed region of the scalar dark matter parameter spaces under the influence of the new Yukawa coupling. The Yukawa coupling associate with the fermion sector heavily dominant the dark matter parameter spaces satisfying the current relic density of the Universe. Dilepton$+slashed{E}_T$ signature arising from the new fermionic sector can observe at Large Hadron Collider (LHC). We perform such analysis in the context of 14 TeV LHC experiments with a future integrated luminosity of 3000 ${rm fb^{-1}}$. We found that a large region of the parameter spaces can be probed by the LHC experiments. The projected exclusion/discovery reach of direct heavy charged fermion searches in this channels is analyzed by performing a detailed cut based collider analysis. The projected exclusion contour reaches up to $1050-1380~{rm GeV}$ for 3000 ${rm fb^{-1}}$ for a light dark matter $mathcal{O}(10)$ GeV from searches in the $ pp rightarrow E_1^pm E_1^mp, E_1^pmrightarrow l^pm S rightarrow ll + slashed{E}_T$ channel.
We investigate quantum vacuum effects for a massive scalar field, induced by two planar boundaries in background of a linearly expanding spatially flat Friedmann-Robertson-Walker spacetime for an arbitrary number of spatial dimensions. For the Robin boundary conditions and for general curvature coupling parameter, a complete set of mode functions is presented and the related Hadamard function is evaluated. The results are specified for the most important special cases of the adiabatic and conformal vacuum states. The vacuum expectation values of the field squared and of the energy-momentum tensor are investigated for a massive conformally coupled field. The vacuum energy-momentum tensor, in addition to the diagonal components, has nonzero off-diagonal component describing energy flux along the direction perpendicular to the plates. The influence of the gravitational field on the local characteristics of the vacuum state is essential at distances from the boundaries larger than the curvature radius of the background spacetime. In contrast to the Minkowskian bulk, at large distances the boundary-induced expectation values follow as power law for both massless and massive fields. Another difference is that the Casimir forces acting on the separate plates do not coincide if the corresponding Robin coefficients are different. At large separations between the plates the decay of the forces is power law. We show that during the cosmological expansion the forces may change the sign.
We present a global study of the simplest scalar phantom dark matter model. The best fit parameters of the model are determined by simultaneously imposing (i) relic density constraint from WMAP, (ii) 225 live days data from direct experiment XENON100, (iii) upper limit of gamma-ray flux from Fermi-LAT indirect detection based on dwarf spheroidal satellite galaxies, and (iv) the Higgs boson candidate with a mass about 125 GeV and its invisible branching ratio no larger than 40% if the decay of the Higgs boson into a pair of dark matter is kinematically allowed. The allowed parameter space is then used to predict annihilation cross sections for gamma-ray lines, event rates for three processes mono-b jet, single charged lepton and two charged leptons plus missing energies at the Large Hadron Collider, as well as to evaluate the muon anomalous magnetic dipole moment for the model.
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