Gravitational Waves From a Dark (Twin) Phase Transition (1504.07263v2)

Abstract: In this work, we show that a large class of models with a composite dark sector undergo a strong first order phase transition in the early universe, which could lead to a detectable gravitational wave signal. We summarise the basic conditions for a strong first order phase transition for SU(N) dark sectors with n_f flavours, calculate the gravitational wave spectrum and show that, depending on the dark confinement scale, it can be detected at eLISA or in pulsar timing array experiments. The gravitational wave signal provides a unique test of the gravitational interactions of a dark sector, and we discuss the complementarity with conventional searches for new dark sectors. The discussion includes Twin Higgs and SIMP models as well as symmetric and asymmetric composite dark matter scenarios.

• The paper presents a detailed model for producing detectable gravitational waves from strong first-order phase transitions in a composite dark sector.
• It employs SU(N) gauge symmetries and investigates scenarios like Twin Higgs and SIMP to elucidate dark sector dynamics in the early universe.
• The study predicts gravitational wave spectra within the sensitivity of upcoming observatories, offering new insights into dark matter research and early cosmic events.

Gravitational Waves From a Dark (Twin) Phase Transition

The paper of gravitational waves (GWs) provides unique insights into cosmic events, offering an additional observational window into the universe's early epochs. The paper, "Gravitational Waves From a Dark (Twin) Phase Transition" by Pedro Schwaller, explores the conditions under which a strong first-order phase transition in a composite dark sector could produce detectable GWs. This work explores the theoretical modeling of such transitions, with significant implications for both particle physics and astrophysical observations.

Theoretical Framework and Model Considerations

The paper proposes a broad class of models involving a dark sector, which undergoes a strong first-order phase transition early in the universe's development. This dark sector is characterized by SU(N) gauge symmetries and includes models such as the Twin Higgs and SIMP scenarios. What distinguishes these models is their ability to produce a GW signal strong enough to be detected by upcoming observational facilities such as eLISA or pulsar timing array experiments.

One highlight of Schwaller's work is the comprehensive analysis of models where the dark sector is composed of strongly interacting particles, potentially leading to strong phase transitions. Unlike the Standard Model at similar temperatures, these dark sectors might experience first-order phase transitions due to variations in particle content and masses, such as the presence of extra flavors of massless Dirac fermions.

Gravitational Wave Spectrum and Detection Prospects

A core outcome of this research is the computation of GW spectra resulting from these phase transitions. The paper predicts that the GWs produced can be within the detectable range of near-future experiments. The crucial parameters influencing detectability include the scale of the confining SU(N) gauge theory (denoted as $\Lambda_d$), the bubble nucleation rate, the velocity of the bubble walls, and the fraction of energy density in gravitational waves at the time of the phase transition.

The paper emphasizes that GWs offer a unique probing tool that can complement traditional dark sector searches. For instance, if the phase transition occurs at temperatures corresponding to the TeV scale, the resultant GWs could be detectable by satellite experiments like eLISA, which are sensitive to the millihertz frequency bands typical of such cosmic events.

Implications and Future Directions

Schwaller's investigation into gravitational waves from dark phase transitions extends the theoretical understanding of strong dynamics beyond the Standard Model. The detection of these GWs would offer critical insights into the properties of dark matter and the nature of early universe phase transitions. Moreover, exploring GWs from dark sectors provides a potential method for identifying physics that might otherwise remain inaccessible through direct detection or collider experiments.

The paper's discussion implies a promising outlook for upcoming gravitational wave observatories, which may soon test these predictions. Observing such GWs would not only validate these models but also open up novel avenues for investigating unexplored aspects of particle physics and cosmology.

This research thus presents a framework that illustrates the interplay between theoretical particle physics and observational cosmology. It invites further exploration into the coupling dynamics in hidden sectors and encourages the development of enhanced computational and experimental methodologies to decode gravitational wave signals. As observational technologies advance, the implications of Schwaller's findings may significantly shape future dark matter research and our understanding of early universe phenomena.