Cosmological phase transition of spontaneous confinement

Kaustubh Agashe, Peizhi Du, Majid Ekhterachian, Soubhik Kumar, Raman Sundrum
2020 Journal of High Energy Physics  
The dynamics of a cosmological (de)confinement phase transition is studied in nearly conformally invariant field theories, where confinement is predominantly spontaneously generated and associated with a light "dilaton" field. We show how the leading contribution to the transition rate can be computed within the dilaton effective theory. In the context of Composite Higgs theories, we demonstrate that a simple scenario involving two renormalization-group fixed points can make the transition
more » ... the transition proceed much more rapidly than in the minimal scenario, thereby avoiding excessive dilution of matter abundances generated before the transition. The implications for gravitational wave phenomenology are discussed. In general, we find that more (less) rapid phase transitions are associated with weaker (stronger) gravitational wave signals. The various possible features of the strongly coupled composite Higgs phase transition discussed here can be concretely modeled at weak coupling within the AdS/CFT dual Randall-Sundrum extra-dimensional description, which offers important insights into the nature of the transition and its theoretical control. These aspects will be presented in a companion paper. Keywords: Beyond Standard Model, Spontaneous Symmetry Breaking, Technicolor and Composite Models ArXiv ePrint: 1910.06238 Open Access, c The Authors. Article funded by SCOAP 3 . JHEP05(2020)086 coupling over a large hierarchy of scales, such as occurs in the domain of an approximate fixed point (FP) of the renormalization group (RG), and plausibly a large-N (color) structure (see reference [15] for a review of large N ). Greater theoretical control of the strong dynamics is then possible if the large-N approximate FP conformal field theory (CFT) has a useful Anti-de Sitter (AdS)/CFT dual description [16] [17] [18] . Indeed, most of the realistic model building has been done in such a dual higher-dimensional Randall-Sundrum (RS) warped spacetime [19] [20] [21] [22] (see [23, 24] for reviews). Another controlled regime, already visible in four dimensional (4D) spacetime without AdS/CFT, occurs if the breaking of approximate conformal invariance by confinement is primarily spontaneous, resulting in a light pseudo Nambu-Goldstone boson (PNGB) "dilaton" field φ [25]. Here, the vacuum expectation value (VEV) φ gives the confinement scale which typifies the masses of generic composites. This structure was first seen in composite Higgs theory in the dual RS formulation in terms of the "radion" [19, 20, 26] . One goal of this paper is to re-analyse the PT using the 4D dilaton effective field theory (EFT) [22, [27] [28] [29] [30] [31] [32] and reasonable physical expectations, as far as possible. In particular, we study the conditions under which the dilaton dynamics dominates the bubble nucleation rate, which competes with the cosmological expansion rate. Ultimately, a fuller description and justification of these expectations involves modeling the deconfined phase, outside the dilaton regime, a task we will re-examine in a forthcoming paper from the RS perspective [33] . This dual description requires large N and yields a more tractable semi-classical, but higher-dimensional description of non-perturbative 4D deconfinement in terms of the AdS-Schwarzschild horizon. The confinement PT then corresponds to bubbles of the RS "IR brane" nucleating and expanding from this horizon [34] . Our 5D analysis [33] will further justify and sharpen the dilaton dominance approximation and account for subleading corrections. Therefore, here, we will track the consistency of our dilaton dominance results with large N . Reference [34] already argued for dilaton dominance in the RS context, but not completely within higher-dimensional EFT control, and they showed that the PT cannot be prompt in the minimal RS model. References [35] [36] [37] showed that the PT could nevertheless complete after a period of supercooling, assuming dilaton dominance (see also [38] [39] [40] [41] [42] for further studies of supercooling). Our results will reinforce the earlier work more systematically. Furthermore, we will also show that having separate approximate RG FP regimes controlling large hierarchies and the PT dynamics can easily result in a more prompt PT than the minimal model, with important consequences for cosmological (dark) matter abundances, GW and collider phenomenology. References [43-47] explored other non-minimal modeling to make the PT complete more promptly. This paper is organized as follows. In section 2, we give the equilibrium description of the confined and deconfined phases, and then in section 3, we calculate the rate of the phase transition between the two phases in the thin-wall regime. We notice that in the minimal composite Higgs models where the Planck-Weak hierarchy is correctly accounted for, the PT does not complete in the thin-wall regime if we demand a theoretically controlled analysis. In such cases, the universe supercools for a very long time and dilutes any preexisting particle abundances. Therefore in section 4, we construct a simple modification
doi:10.1007/jhep05(2020)086 fatcat:cii2ewgimzes3mnm6ka7vo4coq