Collisional Dark Matter and Scalar Phantoms

A classically scale-invariant scalar singlet can be a MeV-scale dark matter, with a feeble Higgs portal coupling at $\mathcal{O}(10^{-10})$. Besides, an $\mathcal{O}(0.1)$ self-interaction coupling could further serve to alleviate the small-scale problems in the Universe. We show that, such a dark matter candidate can naturally arise in the warped extra dimension, with the huge span of parameter space predicted well within $\mathcal{O}(1)$ fundamental parameters.

We show that a gauge singlet scalar S, with a coupling to the Higgs doublet of the form lambda_{S} S^{\dagger}S H^{\dagger}H and with the S mass entirely generated by the Higgs expectation value, has a thermally generated relic density Omega_{S} \approx 0.3 if m_{S} \approx (2.9-10.5)(Omega_{S}/0.3)^{1/5}(h/0.7)^{2/5} MeV for Higgs boson masses in the range 115 GeV to 1 TeV. Remarkably, this is very similar to the range (m_{S} = (6.6-15.4)\eta^{2/3} MeV) required in order for...

A pseudoscalar or scalar particle $\phi$ that couples to two photons but not to leptons, quarks and nucleons would have effects in most of the experiments searching for axions, since these are based on the $a \gamma \gamma $ coupling. We examine the laboratory, astrophysical and cosmological constraints on $\phi$ and study whether it may constitute a substantial part of the dark matter. We also generalize the $\phi$ interactions to possess $SU(2) \times U(1)$ gauge invariance...

A $SU(2)_D \times U(1)_D$ gauge-Higgs sector, an exact dark copy of the Standard Model (SM) one, is proposed. It is demonstrated that the dark gauge bosons ${\cal W}^{(p,m)}$, in analogous to the SM $W^\pm$, can fulfill the role as a self-interacting vector dark matter candidate, solving the core versus cusp and missing satellites problems faced by the conventional paradigm of collisionless weakly interacting massive particle. Constraints from collider, astroparticle and cosm...

We consider dark matter physics in a model for the dark sector with extra dark U(1)$_X$ gauge symmetry. The dark sector is composed of exotic fermions that are charged under both dark U(1)$_X$ and the standard model SU(3)$_C \times$U(1)$_Y$ gauge groups, as well as standard model singlet complex scalars $\Phi$ and $X$ with nonzero U(1)$_X$ charge. In this model, there are two dark matter candidates$-$a scalar and a fermion$-$both of which are stabilized by accidental $Z_2$ sy...

We examine the phenomenology of a simplified model of fermionic dark matter coupled to a light scalar mediator carrying lepton number 2. We find that the mediator can be very light and still consistent with laboratory and cosmological bounds. This model satisfies the thermal relic condition for natural values of dimensionless coupling constants and admits a mediator in the $10 - 100 ~\text{MeV}$ mass range favored by small scale structure observations. As such, this model pro...

One of the simplest models of dark matter is that where a scalar singlet field S comprises some or all of the dark matter, and interacts with the standard model through an HHSS coupling to the Higgs boson. We update the present limits on the model from LHC searches for invisible Higgs decays, the thermal relic density of S, and dark matter searches via indirect and direct detection. We point out that the currently allowed parameter space is on the verge of being significantly...

We construct a self-interacting scalar dark matter (DM) model with local discrete $Z_{3}$ symmetry that stabilizes a weak scale scalar dark matter $X$. The model assumes a hidden sector with a local $U(1)_X$ dark gauge symmetry, which is broken spontaneously into $Z_3$ subgroup by nonzero VEV of dark Higgs field $\phi_X$ ($ \langle \phi_X \rangle \neq 0$). Compared with global $Z_3$ DM models, the local $Z_3$ model has two new extra fields: a dark gauge field $Z^{'}$ and a da...

A short tour of supersymmetric dark matter and its connection to collider physics.

An extension of the Standard Model by extra scalar singlets was considered. Theoretical (unitarity, vacuum stability, triviality) and cosmological (dark matter relic abundance, direct detection experiments, constraints on dark matter self-interaction) constraints were discussed.