Energy budget of cosmological first-order phase transitions

Abstract

The study of the hydrodynamics of bubble growth in first-order phase transitions is very relevant for electroweak baryogenesis, as the baryon asymmetry depends sensitively on the bubble wall velocity, and also for predicting the size of the gravity wave signal resulting from bubble collisions, which depends on both the bubble wall velocity and the plasma fluid velocity. We perform such study in different bubble expansion regimes, namely deflagrations, detonations, hybrids (steady states) and runaway solutions (accelerating wall), without relying on a specific particle physics model. We compute the efficiency of the transfer of vacuum energy to the bubble wall and the plasma in all regimes. We clarify the condition determining the runaway regime and stress that in most models of strong first-order phase transitions this will modify expectations for the gravity wave signal. Indeed, in this case, most of the kinetic energy is concentrated in the wall and almost no turbulent fluid motions are expected since the surrounding fluid is kept mostly at rest.

Bubble expansion and the viability of singlet-driven electroweak baryogenesis

“…5 Recent years have seen progress in matching models onto these existing results [54,[80][81][82] and in the hydrodynamic considerations associated with bubble wall expansion (see e.g. [83][84][85][86][87][88][89]). …”

Probing the baryogenesis and dark matter relaxed in phase transition by gravitational waves and colliders

“…with f * sw = 2β/( √ 3v b ) at T * [22,27], and for relativistic bubbles [28] λ sw α (0.73 + 0.083 √ α + α) −1 . For the turbulence, the peak frequency at T * is about f * tu = 1.75β/v b [27], and the GWs spectrum is formulated by [21,29]…”

Cosmological Signatures of a UV-Conformal Standard Model

“…The velocity v w of the expanding bubbles can be computed by solving a set of hydrodynamic equations [18,21], since the plasma friction on the expanding bubble walls is known for the SM [21]. Stationary state bubbles expand either as subsonic deflagrations or as supersonic detonations (see, e.g., [22]), the sound speed of a relativistic plasma being c s ¼ 1= ffiffi ffi 3 p ∼ 0.577. Subsonic bubbles could potentially lead to baryogenesis for a strong enough EWPT, R n ≳ 1.…”

“…Supersonic bubbles do not allow in general for baryogenesis (see, however, [23]), but collisions of fast moving bubbles at the end of the EWPT can be a powerful source of gravitational waves [24][25][26]. For very strong phase transitions the bubbles become ultrarelativistic and enter a "runaway" (continuously accelerating) regime [27], leading to very efficient gravitational wave production [22].F o r the GMESB scenarios discussed here, we show in Fig. 2 the ranges of X for which deflagrations, detonations, and runaway are realized.…”

“…where g à ≈ 107.75 is the effective number of degrees of freedom in the early Universe, α is the ratio of latent heat to the energy stored in radiation [30], κðα;v w Þ is the efficiency in converting this latent heat into kinetic energy that can lead to GW production as computed in [22],and H à =β corresponds to the mean bubble size (normalized to the Hubble radius). Both α and κ are computed at T à , while β −1 estimates the duration of the EWPT and is usually obtained as the leading order term in the expansion of F c =T in (6) around T à [31].T h i sr e t u r n sa n adequate mean bubble size only when the EWPT proceeds much faster than the rate of expansion of the Universe (H à =β ≪ 1).…”