Higgs portal, fermionic dark matter, and a Standard Model like Higgs at 125 GeV

TL;DR

The paper investigates whether fermionic dark matter can couple to the Standard Model through a Higgs portal while a SM-like Higgs lies near $m_h\approx 125\ \mathrm{GeV}$. It contrasts an EFT treatment with two Higgs-portal operators, $Q_1$ (parity-conserving) and $Q_5$ (parity-violating), showing that direct-detection constraints favor parity-violating interactions in the heavy-mediator limit, whereas parity-conserving scenarios survive only via special UV completions. A renormalizable toy model with a real scalar mediator demonstrates three viable parity-conserving pathways: resonant Higgs portal, indirect Higgs portal, and scenarios with Sommerfeld-enhanced annihilation; in each case a SM-like Higgs is compatible with current direct-detection bounds. The results highlight that a fermionic Higgs portal can still yield a viable WIMP with relic density set by thermal freeze-out, while predicting distinct indirect-detection prospects and potentially suppressed LHC signals in the “LHC nightmare” regime.

Abstract

We show that fermionic dark matter (DM) which communicates with the Standard Model (SM) via the Higgs portal is a viable scenario, even if a SM-like Higgs is found at around 125 GeV. Using effective field theory we show that for DM with a mass in the range from about 60 GeV to 2 TeV the Higgs portal needs to be parity violating in order to be in agreement with direct detection searches. For parity conserving interactions we identify two distinct options that remain viable: a resonant Higgs portal, and an indirect Higgs portal. We illustrate both possibilities using a simple renormalizable toy model.

Figures (4)

• Figure 1: Proton--dark matter scattering cross section as a function of the dark matter mass in the effective field theory of eq. (\ref{['eq:Heff']}), as predicted by requiring that the correct relic density is obtained by thermal freeze-out. The scattering cross section is shown for several ratios of pseudo scalar coupling to scalar coupling $\Lambda_1/\Lambda_5$, and compared to the limit from XENON100 Aprile:2011hi.
• Figure 2: Proton--DM scattering cross section as a function of the dark matter mass in the Higgs portal model for $m_{H_1} = 125$ GeV, $m_{H_2} = 2$ TeV, and $g_P=0$. The green points correspond to a SM-like $H_1$ with an LHC Higgs signal strength modifier $r_1>0.9$, while the red points have $r_1 < 0.9$. The points above the blue line are excluded at 95% CL by the XENON100 experiment Aprile:2011hi. This exclusion limit has been extended for $m_\chi>1$ TeV assuming a linear dependence in $m_\chi$.
• Figure 3: Parameter choices giving rise to a relic density in the WMAP range in the Higgs portal model with $m_{H_1} = 125$ GeV and $g_P=0$. Green and red points correspond to $m_{H_2}<m_\chi$ with a more ($r_1>0.9$) or less ($r_1<0.9$) SM Higgs-like $H_1$, respectively. We show the scalar coupling $g_S$ as a function of the dark matter mass without (left) and with (right) Sommerfeld enhancement for the relic density computation. For illustration, we also show the points with $m_{H_2}>m_\chi$ (blue points).
• Figure 4: Parameter choices giving rise to a relic density in the WMAP range in the Higgs portal model with $m_{H_1} = 125$ GeV and $g_P=0$. Green and red points correspond to $m_{H_2}<m_\chi$ with a more ($r_1>0.9$) or less ($r_1<0.9$) SM Higgs-like $H_1$, respectively. We show the DM--proton scattering cross section as a function of the dark matter mass for $m_{H_2}<m_\chi$ only. The points above the blue line are excluded at 95% CL by the XENON100 experiment Aprile:2011hi. This exclusion limit has been extended for $m_\chi>1$ TeV assuming a linear dependence in $m_\chi$.