Light Higgs Boson, Light Dark Matter and Gamma Rays

TL;DR

This paper argues that a minimal extension of the Standard Model by a complex scalar singlet can simultaneously accommodate a light Higgs and a light dark matter particle. The Complex Scalar Singlet Model (CSM) introduces a singlet that mixes with the SM Higgs, producing a light Higgs state $H_1$ with reduced SM couplings and a heavier Higgs $H_2$, while its CP-odd component $A$ serves as dark matter. By fitting electroweak precision observables, DM direct-detection hints (CoGeNT/DAMA) and the Fermi Gamma-Ray Space Telescope gamma-ray data from the Galactic Center, the model achieves a better agreement than the SM, with an annihilation cross section $\langle v\sigma\rangle_0$ around $1$ pb for light DM and up to $\sim 3\times10^{-25}$ cm$^3$ s$^{-1}$ for $M_A\approx30$ GeV. It also predicts measurable collider signatures, including $H_2$ decays to invisible $AA$ or to $H_1H_1$, offering concrete tests at the LHC and in future gamma-ray observations.

Abstract

A light Higgs boson is preferred by $M_W$ and $m_t$ measurements. A complex scalar singlet addition to the Standard Model allows a better fit to these measurements through a new light singlet dominated state. It then predicts a light Dark Matter (DM) particle that can explain the signals of DM scattering from nuclei in the CoGeNT and DAMA/LIBRA experiments. Annihilations of this DM in the galactic halo, $AA\rightarrow b\bar{b}, c\bar{c}, τ^+τ^-$, lead to gamma rays that naturally improve a fit to the Fermi Large Area Telescope data in the central galactic regions. The associated light neutral Higgs boson may also be discovered at the Large Hadron Collider.

Figures (7)

• Figure 1: The dependence of $M_W$ on $M_H$ for the SM (with $M_H$ above 114 GeV) and on $M_{H}\equiv M_{H_1}$ for the complex singlet model for various values of $\cos^2\phi$ with $M_{H_2}=114$ GeV. The values of $m_t,M_Z, \Delta\alpha$ and $\alpha_s$ are fixed to their central values.
• Figure 2: Contours of the World's average $m_t$ and $M_W$ at the $1\sigma$ and $2\sigma$ levels. The SM (red dashed line) shows consistency with the measurements at about $2\sigma$. The two CSM illustrations (brown and blue dashed lines ) give an improved description of the data via the light Higgs state that has a singlet admixture characterized by the mixing angle $\phi$.
• Figure 3: The (a) maximal SM Higgs content of the lightest Higgs after LEP constraints are applied and (b) the predicted $W$-boson mass given in the maximal-mixing and no-mixing cases.
• Figure 4: The CSM population (all points) on the $\left< v\sigma\right>_0$ vs $\sigma_{SI}$ plane that reproduces the relic density observed by WMAP7 and the XENON100 exclusion limit on $\sigma_{SI}$. The CoGeNT allowed points are marked as blue dots (right). The points with 27$<M_A<$33 GeV are marked a black '+'s (left) that better explains the FGST gamma ray spectra.
• Figure 5: Differential gamma ray spectra from individual channels for a 10 GeV $M_A$. Although sub-dominant to the $b\bar{b}$ channel, the $\tau^+\tau^-$ channel produces more hard photons at energy fraction $x>0.5$ through copious $\pi^0$ decays