BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Isabel Garcia Garcia (University of California - Santa Barbara) DTSTART:20221206T193000Z DTEND:20221206T203000Z DTSTAMP:20260423T004757Z UID:nhetc/55 DESCRIPTION:Title: T he Rocket Science of Bubble Walls\nby Isabel Garcia Garcia (University of California - Santa Barbara) as part of NHETC Seminar\n\n\nAbstract\nCo smological phase transitions that proceed via nucleation of bubbles are a well-motivated possibility both in minimal extensions of the Standard Mode l as well as in more general hidden sectors with their own dynamics. Such an event produces a stochastic background of gravitational radiation that could be observed by current and future observatories. That said\, our abi lity to extract any detailed information about the underlying dynamics fro m such an observation is extremely limited\, and highlights the necessity of (i) better understanding the dynamics of bubble walls in the early Univ erse\, given their impact on the high-frequency shape of the signal\, and (ii) exploring complementary probes of an observable gravitational wave ba ckground.\n\nIn this talk\, I will discuss the dynamics of expanding vacuu m bubbles in the presence of massive vectors (a.k.a. dark photons) that ga in mass across the interface -- with a special focus on the well-motivated benchmark where the dark photons furnish the dark matter. I will argue th e existence of a transient kinematic regime during which the wall behaves as an (imperfect) mirror of longitudinal -- but not transverse -- modes. M ost notably\, this leads to a new source of pressure on the expanding inte rface that can prevent the accelerated expansion of the bubble walls. Inst ead of accelerating the interface\, the difference in vacuum energy densit y across the wall goes into making a fraction of the dark photons relativi stic\, turning them into dark radiation. The corresponding value of \\Delt a N_eff is determined by the strength of the phase transition and the epoc h at which the transition takes place. Current \\Delta N_eff constraints c an rule out phase transitions with strength \\alpha \\simeq 0.1\, whereas CMB S-4 measurements will probe scenarios down to \\alpha = 0.01 for all r elevant frequencies.\n\nThis talk is based on arXiv:2212.xxxxx in collabor ation with Giacomo Koszegi and Rudin Petrossian-Byrne.\n LOCATION:https://researchseminars.org/talk/nhetc/55/ END:VEVENT END:VCALENDAR