分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The current LIGO-Virgo observing run has been pushing the sensitivity limit to touch the stochastic gravitational-wave backgrounds (SGWBs). However, no significant detection has been reported to date for any single dominated source of SGWBs with a single broken-power-law (BPL) spectrum. Nevertheless, it could equally well escape from existing Bayesian searches from, for example, two comparable dominated sources with two separate BPL spectra (double-peak case) or a single source with a doubly-BPL (DBPL) spectrum (doubly-broken case). In this paper, we put constraints on these two cases from Advanced LIGO-Virgo's first three observing runs. We found strong negative evidence for the double-peak case and hence place 95\% confidence-level (CL) upper limits $\Omega_\mathrm{BPL,1}<2.5\times10^{-7}$ and $\Omega_\mathrm{BPL,2}<9.4\times10^{-8}$ on the two BPL spectra amplitudes with respect to the unresolved compact-binary-coalescence (CBC) amplitude $\Omega_\mathrm{CBC}<5.6\times10^{-9}$. We further found weak negative evidence for the doubly-broken case and hence place 95\% CL upper limit $\Omega_\mathrm{DBPL}<1.7\times10^{-7}$ on the overall amplitude of the DBPL spectrum with respect to $\Omega_\mathrm{CBC}<6.0\times10^{-9}$. The implications of cosmological first-order phase transitions are also discussed.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The sample variance due to our local density fluctuations in measuring our local Hubble-constant ($H_0$) can be reduced to the percentage level by choosing the Hubble-flow type Ia supernovae (SNe Ia) outside of the homogeneity scale. In this Letter, we have revealed a hidden trend in this one-percent $H_0$ variation both theoretically and observationally. We have derived for the first time our $H_0$ variation measured from any discrete sample of distant SNe Ia. We have also identified a residual linear correlation between our local $H_0$ fitted from different groups of SNe Ia and their ambient density contrasts of SN-host galaxies evaluated at a given scale. We have further traced the scale dependence of this residual linear trend, which becomes more and more positively correlated with the ambient density contrasts of SN-host galaxies estimated at larger and larger scales, on the contrary to but still marginally consistent with the theoretical expectation from the $\Lambda$-cold-dark-matter model. This might indicate some unknown corrections to the peculiar velocity of the SN-host galaxy from the density contrasts at larger scales or the smoking gun for the new physics.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The cosmological first-order phase transition (FOPT) can be of strong dynamics but with its bubble wall velocity difficult to be determined due to lack of detailed collision terms. Recent holographic numerical simulations of strongly coupled theories with a FOPT prefer a relatively small wall velocity linearly correlated with the phase pressure difference between false and true vacua for a planar wall. In this Letter, we have analytically revealed the non-relativistic limit of a planar/cylindrical/spherical wall expansion of a bubble strongly interacting with the thermal plasma. The planar-wall result reproduces the linear relation found previously in the holographic numerical simulations. The results for cylindrical and spherical walls can be directly tested in future numerical simulations. Once confirmed, the bubble wall velocity for a strongly coupled FOPT can be expressed purely in terms of the hydrodynamics without invoking the underlying microphysics.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We construct a holographic model describing the gluon sector of Yang-Mills theories at finite temperature in the non-perturbative regime. The equation of state as a function of temperature is in good accordance with the lattice quantum chromodynamics (QCD) data. Moreover, the Polyakov loop and the gluon condensation, which are proper order parameters to capture the deconfinement phase transition, also agree quantitatively well with the lattice QCD data. We obtain a strong first-order confinement/deconfinement phase transition at $T_c=276.5\,\text{MeV}$ that is consistent with the lattice QCD prediction. The resulting stochastic gravitational-wave backgrounds from this confinement/deconfinement phase transition are obtained with potential detectability in the International Pulsar Timing Array and Square Kilometre Array in the near future when the associated productions of primordial black holes (PBHs) saturate the current observational bounds on the PBH abundances from the LIGO-Virgo-Collaboration O3 data.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-09-27
摘要： The measured masses of the Higgs boson and top quark indicate that the e#11;ective potential of the standard model either develops an unstable electroweak vacuum or stands stable all the way up to the Planck scale. In the latter case in which the top quark mass is about 2#27; below its present central value, the Higgs boson can be the inaton with the help of a large nonminimal coupling to curvature in four dimensions. We propose a scenario in which the Higgs boson can be the in aton in a#12;ve-dimensional Gauss-Bonnet braneworld model to solve both the unitarity and stability problems which usually plague Higgs ination. We #12;nd that in order for Higgs ination to happen successfully in the Gauss-Bonnet regime, the extra dimension scale must appear roughly in the range between the TeV scale and the instability scale of standard model. At the tree level, our model can give rise to a naturally small nonminimal coupling #24; #24; O(1) for the Higgs quartic coupling #21; #24; O(0:1) if the extra dimension scale lies at the TeV scale. At the loop level, the in ationary predictions at the treelevel are preserved. Our model can be confronted with future experiments and observations fromboth particle physics and cosmology.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-09-27
摘要： We investigate the in uence on the in ationary predictions from the reheating processes char-acterized by the e-folding number Nreh and the e ective equation-of-state parameter wreh during the reheating phase. For the rst time, reheating processes can be constrained in the Nreh wreh plane from Planck 2015. We nd that for Higgs in ation with a nonminimal coupling to gravity, the predictions are insensitive to the reheating phase for current CMB measurements. We also nd that the spontaneously broken SUSY in ation and axion monodromy in ation with 2=3 potential, which with instantaneous reheating lie outside or at the edge of the 95% con dence region in the ns r plane from Planck 2015 TT,TE,EE+lowP, can well t the data with the help of reheating processes. Future CMB experiments would put strong constraints on reheating processes.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We investigate the curvature perturbations induced by the randomness of the quantum tunneling process during cosmological first-order phase transitions (PTs) and for the first time ultilize curvature perturbations to constrain the PT parameters. We find that the observations of the cosmic microwave background spectrum distortion and the ultracompact minihalo abundance can give strict constraints on the PTs below 100GeV, especially for the low-scale PTs and the weak PTs. The current constraint on the PT parameters is largely extended by the results in this work.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-09-27
摘要： The direct detection of gravitational wave by Laser Interferometer Gravitational-Wave Observatory indicates the coming of the era of gravitational-wave astronomy and gravitational-wave cosmology. It is expected that more and more gravitational-wave events will be detected by currently existing and planned gravitational-wave detectors. The gravitational waves open a new window to explore the Universe and various mysteries will be disclosed through the gravitational-wave detection, combined with other cosmological probes. The gravitational-wave physics is not only related to gravitation theory, but also is closely tied to fundamental physics, cosmology and astrophysics. In this review article, three kinds of sources of gravitational waves and relevant physics will be discussed, namely gravitational waves produced during the inflation and preheating phases of the Universe,the gravitational waves produced during the first-order phase transition as the Universe cools down and the gravitational waves from the three phases: inspiral, merger and ringdown of a compact binary system, respectively. We will also discuss the gravitational waves as a standard siren to explore the evolution of the Universe.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Values of the Hubble constant between the direct measurements from various independent local observations and that inferred from the cosmic microwave background with the $\Lambda$-cold-dark-matter model are in tension with persistent significance. We propose a late-time inhomogeneous resolution suggesting that a chameleon field coupled to a local overdensity of matter could be trapped at a higher potential energy density as an effective cosmological constant driving the local expansion rate faster than that of the background with lower matter density. We illustrate this mechanism in a toy model in which a region with only $20\%$ overdensity of matter is sufficient to resolve the Hubble tension, and the Hubble constant measured by the local distance ladders could be accommodated by the chameleon coupled to the observed overdensities from the large-scale structure surveys.
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