Gravitational waves from the asymmetric-dark-matter generating phase transition

Abstract

The baryon asymmetry, together with a dark matter asymmetry, may be produced during a first order phase transition in a generative sector. We study the possibility of a gravitational wave signal in a model realising such a scenario. We identify areas of parameter space with strong phase transitions which can be probed by future, space based, gravitational wave detectors. Other signals of this scenario include collider signatures of a $Z'$, DM self interactions, a contribution to $ΔN_{\rm eff}$ and nuclear recoils at direct detection experiments.

Figures (3)

• Figure 1: Contours of $\phi_{n}/T_{n}$ (thick grey lines) for the $\phi^{6}$ tree level potential of eq. (\ref{['eq:v6pot']}). The washout condition of eq. (\ref{['eq:washoutcondition']}) is satisfied for $\phi_{n}/T_{n}\gtrsim 1.5 - 1.8$. The red area does not lead to symmetry breaking as $V_{\rm eff}^{T=0}(v_{\phi})>V_{\rm eff}^{T=0}(0)$. The orange region is either meta-stable and does not lead to a thermal transition or it leads to a runaway transition. The green area returns a gravitational wave spectrum with a BBO signal to noise ratio (SNR) $>5$. The SNR for gravitational waves has been calculated with $\mu_{\phi}=100$ GeV, while all other contours are independent of $\mu_{\phi}$, see sections \ref{['sec:gw']} and \ref{['sec:scaling']} for details. Note we have used an optimistic value for the wall velocity, $v_{w}=1/\sqrt{3}$, in calculating the SNR. The blue points are where we also find a LISA SNR $>5$. These always occur close to runaway transitions in this model. Hence LISA is only sensitive to a very small portion of the parameter space of this model.
• Figure 2: Example of the gravitational wave spectrum for different wall velocities and estimated sensitivity of LISA (C1) Caprini:2015zlo and BBO Thrane:2013oya to stochastic power law backgrounds. The input parameters correspond to the lowest of the blue points in figure \ref{['fig:phi6_scan']}. This point is close to the runaway boundary so a deflagration, with $v_{w} < 1/\sqrt{3}$ is actually unlikely, which illustrates the difficulty in obtaining a signal observable by LISA and consistent with baryogenesis in this model.
• Figure 3: Predicted resonant $Z'$ dilepton signal and limit from the ATLAS ATLAS-CONF-2016-045 (CMS gives similar limits Khachatryan:2016zqb). The intrinsic width of the resonance is $\Gamma_{Z'}\approx 0.3 \%, \; 2.9 \%, \; 11 \%$ of $M_{Z'}$ for gauge couplings $g_{B-L}=0.1, \; 0.3, \; 0.6$ respectively.