71 research outputs found
Gravitational waves from bubble dynamics: Beyond the envelope
No full textWe study gravitational-wave production from bubble dynamics (bubble collisions and sound waves) during a cosmic first-order phase transition with an analytic approach. We first propose modeling the system with the thin-wall approximation but without the envelope approximation often adopted in the literature, in order to take bubble propagation after collisions into account. The bubble walls in our setup are considered as modeling the scalar field configuration and/or the bulk motion of the fluid. We next write down analytic expressions for the gravitational-wave spectrum, and evaluate them with numerical methods. It is found that, in the long-lasting limit of the collided bubble walls, the spectrum grows from f 3 to f 1 in low frequencies, showing a significant enhancement compared to the one with the envelope approximation. It is also found that the spectrum saturates in the same limit, indicating a decrease in the correlation of the energy-momentum tensor at late times. We also discuss the implications of our results to gravitational-wave production both from bubble collisions (scalar dynamics) and sound waves (fluid dynamics). © 2019 IOP Publishing Ltd and Sissa Medialab11Nsciescopu
Hill-climbing inflation
No full textWe propose a new class of inflationary models in which inflation takes place while the inflaton is climbing up a potential hill due to a coupling to gravity. We study their attractor behavior, and investigate its relation with known attractors. We also discuss a possible realization of this type of models with natural inflation, and show that the inflationary predictions come well within the region consistent with the observation of the cosmic microwave background. © 2017 American Physical Society7711Nsciescopu
Hillclimbing inflation in metric and Palatini formulations
No full textA new setup of cosmic inflation with a periodic inflaton potential and conformal factor is discussed in the metric and Palatini formulations of gravity. As a concrete example, we focus on a natural-inflation-like inflaton potential, and show that the inflationary predictions fall into the allowed region of cosmic microwave background observations in both formulations
Violent preheating in inflation with nonminimal coupling
No full textWe study particle production at the preheating era in inflation models with nonminimal coupling ξφ2R and quartic potential λφ4/4 for several cases: real scalar inflaton, complex scalar inflaton and Abelian Higgs inflaton. We point out that the preheating proceeds much more violently than previously thought. If the inflaton is a complex scalar, the phase degree of freedom is violently produced at the first stage of preheating. If the inflaton is a Higgs field, the longitudinal gauge boson production is similarly violent. This is caused by a spike-like feature in the time dependence of the inflaton field, which may be understood as a consequence of the short time scale during which the effective potential or kinetic term changes suddenly. The produced particles typically have very high momenta k ≲ √λMP. The production might be so strong that almost all the energy of the inflaton is carried away within one oscillation for ξ2λ ≳ O(100). This may partly change the conventional understandings of the (p)reheating after inflation with the nonminimal coupling to gravity such as Higgs inflation. We also discuss the possibility of unitarity violation at the preheating stage. © 2017 IOP Publishing Ltd and Sissa Medialab srl101311Nsciescopu
Hill-climbing Higgs inflation
No full textWe propose a realization of cosmic inflation with the Higgs field when the Higgs potential has degenerate vacua by employing the recently proposed idea of hill-climbing inflation. The resultant inflationary predictions exhibit a sizable deviation from those of the ordinary Higgs inflation. © 2018 authors. Published by the American Physical Society1111Nsciescopu
Gravitational waves from first-order phase transitions: towards model separation by bubble nucleation rate
No full textWe study gravitational-wave production from bubble collisions in a cosmic first-order phase transition, focusing on the possibility of model separation by the bubble nucleation rate dependence of the resulting gravitational-wave spectrum. By using the method of relating the spectrum with the two-point correlator of the energy-momentum tensor , we first write down analytic expressions for the spectrum with a Gaussian correction to the commonly used nucleation rate, Gamma proportional to e(beta t) -> e(beta t-gamma 2t2), under the thin-wall and envelope approximations. Then we quantitatively investigate how the spectrum changes with the size of the Gaussian correction. It is found that the spectral shape shows O(10)% deviation from Gamma proportional to e(beta t) case for some physically motivated scenarios. We also briefly discuss detector sensitivities required to distinguish different spectral shapes
(c) 2017 IOP Publishing Ltd and Sissa Medialab6611Nsciescopu
Gravitational waves from first-order phase transitions: ultra-supercooled transitions and the fate of relativistic shocks
No full textWe study the gravitational wave (GW) production in extremely strong first order phase transitions where the vacuum energy density dominates the plasma energy density, alpha greater than or similar to 1. In such transitions, bubbles develop extremely thin and relativistic fluid configurations, resulting in strong shock waves after collisions. We first propose a strategy to understand the GW production in such a system by separating the problem into the propagation part and the collision part. Focusing on the former, we next develop an effective theory for the propagation of the relativistic fluid shells. Using this effective theory, we finally calculate the expected duration of the relativistic fluid configurations and discuss its implications to the GW production. c 2019 IOP Publishing Ltd and Sissa Medialab11Nsciescopu
Higgs inflation in metric and Palatini formalisms: Required suppression of higher dimensional operators
No full textWe investigate the sensitivity of Higgs(-like) inflation to higher dimensional operators in the nonminimal couplings and in the potential, both in the metric and Palatini formalisms. We find that, while inflationary predictions are relatively stable against the higher dimensional operators around the attractor point in the metric formalism, they are extremely sensitive in the Palatini one: for the latter, inflationary predictions are spoiled by in the nonminimal couplings , or by in the Jordan-frame potential (both in Planck units). This extreme sensitivity results from the absence of attractor in the Palatini formalism. Our study underscores the challenge of realizing inflationary models with the nonminimal coupling in the Palatini formalism
Fingerprint matching of beyond-WIMP dark matter: neural network approach
No full textGalactic-scale structure is of particular interest since it provides important clues to dark matter properties and its observation is improving. Weakly interacting massive particles (WIMPs) behave as cold dark matter on galactic scales, while beyond-WIMP candidates suppress galactic-scale structure formation. Suppression in the linear matter power spectrum has been conventionally characterized by a single parameter, the thermal warm dark matter mass. On the other hand, the shape of suppression depends on the underlying mechanism. It is necessary to introduce multiple parameters to cover a wide range of beyond-WIMP models. Once multiple parameters are introduced, it becomes harder to share results from one side to the other. In this work, we propose adopting neural network technique to facilitate the communication between the two sides. To demonstrate how to work out in a concrete manner, we consider a simplified model of light feebly interacting massive particles
Selecting models of first-order phase transitions using the synergy between collider and gravitational-wave experiments
No full text© 2019 authors. Published by the American Physical Society.r(s) and the published article's title, journal citation, and DOI. Funded by SCOAP 3 . We investigate the sensitivity of future space-based interferometers such as LISA and DECIGO to the parameters of new particle physics models which drive a first-order phase transition in the early Universe. We first perform a Fisher matrix analysis on the quantities characterizing the gravitational-wave spectrum resulting from the phase transition, such as the peak frequency and amplitude. We next perform a Fisher analysis for the quantities which determine the properties of the phase transition, such as the latent heat and the time dependence of the bubble nucleation rate. Since these quantities are determined by the model parameters of the new physics, we can estimate the expected sensitivities to such parameters. We illustrate this point by taking three new physics models for example: (i) models with additional isospin singlet scalars, (ii) a model with an extra real Higgs singlet, and (iii) a classically conformal B-L model. We find that future gravitational-wave observations play complementary roles to future collider experiments in pinning down the parameters of new physics models driving a first-order phase transition11Nsciescopu
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