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Register a new userGravitational waves from dark Yang-Mills sectors
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Dark Yang-Mills sectors, which are ubiquitous in the string landscape, may be reheated above their critical temperature and subsequently go through a confining first-order phase transition that produces stochastic gravitational waves in the early universe. Taking into account constraints from lattice and from Yang-Mills (center and Weyl) symmetries, we use a phenomenological model to construct an effective potential of the semi quark-gluon plasma phase, from which we compute the gravitational wave signal produced during confinement for numerous gauge groups. The signal is maximized when the dark sector dominates the energy density of the universe at the time of the phase transition. In that case, we find that it is within reach of the next-to-next generation of experiments (BBO, DECIGO) for a range of dark confinement scales near the weak scale.
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We pave the way for future gravitational-wave detection experiments, such as the Big Bang Observer and DECIGO, to constrain dark sectors made of SU(N) Yang-Mills confined theories. We go beyond the state-of-the-art by combining first principle lattice results and effective field theory approaches to infer essential information about the non-perturbative dark deconfinement phase transition driving the generation of gravitational-waves in the early universe, such as the order, duration and energy budget of the phase transition which are essential in establishing the strength of the resulting gravitational-wave signal.
Spectra of stochastic gravitational waves (GW) generated in cosmological first-order phase transitions are computed within strongly correlated theories with a dual holographic description. The theories are mostly used as models of dark sectors. In particular, we consider the so-called Witten-Sakai-Sugimoto model, a $SU(N)$ gauge theory coupled to different matter fields in both the fundamental and the adjoint representations. The model has a well-known top-down holographic dual description which allows us to perform reliable calculations in the strongly coupled regime. We consider the GW spectra from bubble collisions and sound waves arising from two different kinds of first-order phase transitions: a confinement/deconfinement one and a chiral symmetry breaking/restoration one. Depending on the model parameters, we find that the GW spectra may fall within the sensibility region of ground-based and space-based interferometers, as well as of Pulsar Timing Arrays. In the latter case, the signal could be compatible with the recent potential observation by NANOGrav. When the two phase transitions happen at different critical temperatures, characteristic spectra with double frequency peaks show up. Moreover, in this case we explicitly show how to correct the redshift factors appearing in the formulae for the GW power spectra to account for the fact that adiabatic expansion from the first transition to the present times cannot be assumed anymore.
We calculate for the first time the scattering cross section between lightest glueballs in $SU(2)$ pure Yang-Mills theory, which are good candidates of dark matter. In the first step, we evaluate the interglueball potential on lattice using the HAL QCD method, with several lattice spacings ($beta = 2.1, 2.2, 2.3, 2.4$, and 2.5). The systematics associated with nonzero angular momentum effect is removed by subtracting the centrifugal force. The statistical accuracy is improved by employing the cluster-decomposition error reduction technique and by using all space-time symmetries. We then determine the low energy glueball effective Lagrangian and the scattering cross section at low energy, which is compared with the observational constraint on the dark matter self-scattering. We derive the lower bound on the scale parameter of the $SU(2)$ Yang-Mills theory, as $Lambda > 60$ MeV.
We study the spectrum of gravitational waves produced by a first order phase transition in a hidden sector that is colder than the visible sector. In this scenario, bubbles of the hidden sector vacuum can be nucleated through either thermal fluctuations or quantum tunnelling. If a cold hidden sector undergoes a thermally induced transition, the amplitude of the gravitational wave signal produced will be suppressed and its peak frequency shifted compared to if the hidden and visible sector temperatures were equal. This could lead to signals in a frequency range that would otherwise be ruled out by constraints from big bang nucleosynthesis. Alternatively, a sufficiently cold hidden sector could fail to undergo a thermal transition and subsequently transition through the nucleation of bubbles by quantum tunnelling. In this case the bubble walls might accelerate with completely negligible friction. The resulting gravitational wave spectrum has a characteristic frequency dependence, which may allow such cold hidden sectors to be distinguished from models in which the hidden and visible sector temperatures are similar. We compare our results to the sensitivity of the future gravitational wave experimental programme.
We study the dynamics of the Peccei-Quinn (PQ) phase transition for the QCD axion. In weakly coupled models the transition is typically second order except in the region of parameters where the PQ symmetry is broken through the Coleman-Weinberg mechanism. In strongly coupled realizations the transition is often first order. We show examples where the phase transition leads to strong supercooling lowering the nucleation temperature and enhancing the stochastic gravitational wave signals. The models predict a frequency peak in the range 100-1000 Hz with an amplitude that is already within the sensitivity of LIGO and can be thoroughly tested with future gravitational wave interferometers.
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