arXiv subjects

Youping Wan

Publications and source records attributed to Youping Wan.

7 recordsLinked to original sources

arXiv2018

Two-field cosmological phase transitions and gravitational waves in the singlet Majoron model

In the singlet Majoron model, we study cosmological phase transitions (PTs) and their resulting gravitational waves (GWs), in the two-field phase space, without freezing any of the field directions. We first calculate the effective potential, at one loop and at finite temperature, of the Standard Model Higgs doublet together with one extra Higgs singlet. We make use of the public available Python package CosmoTransitions to simulate the two-dimensional cosmological PTs and evaluate the gravitational waves generated by first-order PTs. With the full 2D simulation, we are able not only to confirm the PTs' properties previously discussed in the literature, but also we find new patterns, such as strong first-order PTs tunneling from a vacuum located on one axis to another vacuum located on the second axis. The two-field phase space analysis presents a richer panel of cosmological PT patterns compared to analysis with a single-field approximation. The PTGW amplitudes turn out to be out of the reach for the space-borne gravitational wave interferometers such as LISA, DECIGO, BBO, TAIJI and TianQin when constraints from colliders physics are taken into account.

hep-ph↗

arXiv2016

The Effective Field Theory of nonsingular cosmology

In this paper, we explore the nonsingular cosmology within the framework of the Effective Field Theory(EFT) of cosmological perturbations. Due to the recently proved no-go theorem, any nonsingular cosmological models based on the cubic Galileon suffer from pathologies. We show how the EFT could help us clarify the origin of the no-go theorem, and offer us solutions to break the no-go. Particularly, we point out that the gradient instability can be removed by using some spatial derivative operators in EFT. Based on the EFT description, we obtain a realistic healthy nonsingular cosmological model, and show the perturbation spectrum can be consistent with the observations.

gr-qc↗

arXiv2016

Hearing the echoes of electroweak baryogenesis with gravitational wave detectors

We report on the first joint analysis of observational signatures from the electroweak baryogenesis in both gravitational wave (GW) detectors and particle colliders. With an effective extension of the Higgs sector in terms of the dimension-6 operators, we derive a strong first-order phase transition in associated with a sizable CP violation to realize a successful electroweak baryogenesis. We calculate the GW spectrum resulting from the bubble nucleation, plasma transportation, and magnetohydrodynamic turbulence of this process that occurred after the big bang, and find that it yields GW signals testable in Evolved Laser Interferometer Space Antenna, Deci-hertz Interferometer Gravitational wave Observatory and Big Bang Observer. We further identify collider signals from the same mechanism that are observable at the planning Circular Electron Positron Collider. Our analysis bridges astrophysics/cosmology with particle physics by providing significant motivation for searches for GW event peaking at the $(10^{-4}, 1)$ Hz range, which are associated with signals at colliders, and highlights the possibility of an interdisciplinary observational window into baryogenesis. The technique applied in analyzing early universe phase transitions may enlighten the study of phase transitions in applied science.

hep-ph↗

arXiv2015

Bounce Inflation Cosmology with Standard Model Higgs Boson

It is of great interest to connect cosmology in the early universe to the Standard Model of particle physics. In this paper, we try to construct a bounce inflation model with the standard model Higgs boson, where the one loop correction is taken into account in the effective potential of Higgs field. In this model, a Galileon term has been introduced to eliminate the ghost mode when bounce happens. Moreover, due to the fact that the Fermion loop correction can make part of the Higgs potential negative, one naturally obtains a large equation of state(EoS) parameter in the contracting phase, which can eliminate the anisotropy problem. After the bounce, the model can drive the universe into the standard higgs inflation phase, which can generate nearly scale-invariant power spectrum.

gr-qc↗

arXiv2015

Nonsingular Cosmology from an Unstable Higgs Field

The observed value of the Higgs mass indicates an instability of the Higgs scalar at large energy scales, and hence also at large field values. In the context of early universe cosmology, this is often considered to lead to problems. Here we point out that we can use the instability of the Higgs field to generate an Ekpyrotic phase of contraction. In the context of string theory it is possible that at very high energy densities extra states become massless, leading to an S-brane which leads to the transition between a contracting phase in the past and the current expanding phase. Thus, the Higgs field can be used to generate a non-singular bouncing cosmology in which the anisotropy problem of usual bouncing scenarios is mitigated.

hep-th↗

arXiv2014

Single field inflation with modulated potential in light of the Planck and BICEP2

The recently released BICEP2 data detected the primordial B-mode polarization in the Cosmic Microwave Background (CMB) map which strongly supports for a large tensor-to-scalar ratio, and thus, is found to be in tension with the Planck experiment with no evidence of primordial gravitational waves. Such an observational tension, if confirmed by forthcoming measurements, would bring a theoretical challenge for the very early universe models. To address this issue, we in the present paper revisit a single field inflation model, which includes a modulated potential. We show that this inflation model can give rise to a sizable negative running behavior for the spectral index of primordial curvature perturbation and a large tensor-to-scalar ratio. Applying these properties, our model can nicely explain the combined Planck and BICEP2 observations. To examine the validity of analytic calculations, we numerically confront the predicted temperature and B-mode power spectra with the latest CMB observations and explicitly show that our model is consistent with the current data.

astro-ph.CO↗

arXiv2013

Cosmology of the Spinor Emergent Universe and Scale-invariant Perturbations

A nonsingular emergent universe cosmology can be realized by a nonconventional spinor field as first developed in \cite{Cai:2012yf}. We study the mechanisms of generating scale-invariant primordial power spectrum of curvature perturbation in the frame of spinor emergent universe cosmology. Particularly, we introduce a light scalar field of which the kinetic term couples to the bilinear of the spinor field. This kinetic coupling can give rise to an effective "Hubble radius" for primordial fluctuations from the scalar field to squeeze at large length scales as well as to form a nearly scale-invariant power spectrum. We study the stability of the backreaction and constrain the forms of the coupling terms. These almost scale-independent fluctuations are able to be transferred into curvature perturbation after the epoch of emergent universe through a generalized curvaton mechanism and thus can explain cosmological observations.

hep-th↗