分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The primordial black hole (PBH) productions from the inflationary potential with an inflection point usually rely heavily on the fine-tuning of the model parameters. We propose in this work a new kind of the $\alpha$-attractor inflation with asymmetric double poles that naturally lead to two periods of the standard slow-roll phases connected by a non-attractor ultra-slow-roll phase, during which the PBH productions are guaranteed without fine-tuning the model parameters. This double-pole inflation can be tested against the observational data in the future with rich phenomenological signatures: (1) the enhanced curvature perturbations at small scales admit a distinctive feature of ultraviolet oscillations in the power spectrum; (2) the quasi-monochromatic mass function of the produced PBHs can be made compatible to the asteroid-mass PBHs as the dominant dark matter component, the planet-mass PBHs as the OGLE ultrashort-timescale microlensing events, and the solar-mass PBHs as the LIGO events; (3) the induced gravitational waves can be detected by the gravitational-wave detectors in space and Pulsar Timing Array/Square Kilometer Array.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： As a promising probe for the new physics beyond the standard model of particle physics in the early Universe, the predictions for the stochastic gravitational wave background from a cosmological first-order phase transition heavily rely on the bubble wall velocity determined by the bubble expansion dynamics. The bubble expansion dynamics is governed by the competition between the driving force from the effective potential difference and the backreaction force from a sum of the thermal force and friction force induced by the temperature jumping and out-of-equilibrium effects across the bubble wall, respectively. In this paper, we propose a hydrodynamic evaluation on this total backreaction force for a non-runaway steady-state bubble expansion, which, after evaluated at the wall interface, exactly reproduces the pressure difference $\Delta_\mathrm{wall}[(\bar{\gamma}^2-1)w]$ obtained previously from the junction condition of the total energy-momentum tensor at the wall interface, where $w$ is the enthalpy and $\bar{\gamma}\equiv(1-\bar{v}^2)^{-1/2}$ is the Lorentz factor of the wall-frame fluid velocity $\bar{v}$.
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 stochastic gravitational-wave backgrounds (SGWBs) from the cosmological first-order phase transitions (FOPTs) serve as a promising probe for the new physics beyond the standard model of particle physics. When most of the bubble walls collide with each other long after they had reached the terminal wall velocity, the dominated contribution to the SGWBs comes from the sound waves characterized by the efficiency factor of inserting the released vacuum energy into the bulk fluid motions. However, the previous works of estimating this efficiency factor have only considered the simplified case of the constant sound velocities in both symmetric and broken phases, either for the bag model with equal sound velocities or $\nu$-model with different sound velocities in the symmetric and broken phases, which is unrealistic from a viewpoint of particle physics. In this paper, we propose to solve the fluid EoM with an iteration method when taking into account the sound-velocity variation across the bubble wall for a general and realistic equation of state (EoS) beyond the simple bag model and $\nu$-model. We have found a suppression effect for the efficiency factor of bulk fluid motions, though such a suppression effect could be negligible for the strong FOPT, in which case the previous estimation from a bag EoS on the efficiency factor of bulk fluid motions still works as a good approximation.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The accretion of dark matter around the primordial black holes (PBHs) could lead to the formation of surrounding minihalos, whose mass can be several orders of magnitude higher than the central PBH mass. The gravitational microlensing produced by such dressed PBHs could be quite different from that of the bare PBHs, which may significantly affect the constraints on the PBH abundance. In this paper, we study the gravitational microlensing produced by dressed PBHs in detail. We find that all the microlensing effects by dressed PBHs have asymptotic behavior depending on the minihalo size, which can be used to predict the microlensing effects by comparing the halo size with the Einstein radius. When the minihalo radius and the Einstein radius are comparable, the effect of the density distribution of the halo is significant to the microlensing. Applying the stellar microlensing by dressed PBHs to the data of the Optical Gravitational Lensing Experiment and Subaru/HSC Andromeda observations, we obtain the improved constraints on the PBH abundance. It shows that the existence of dark matter minihalos surrounding PBHs can strengthen the constraints on the PBH abundance from stellar microlensing by several orders, and can shift the constraints to the well-known asteroid mass window where PBHs can constitute all the dark matter.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： As a promising probe for the new physics beyond the standard model of particle physics in the early Universe, the predictions for the stochastic gravitational wave background from a cosmological first-order phase transition heavily rely on the bubble wall velocity determined by the bubble expansion dynamics. The bubble expansion dynamics is governed by the competition between the driving force from the effective potential difference and the backreaction force from a sum of the thermal force and friction force induced by the temperature jumping and out-of-equilibrium effects across the bubble wall, respectively. In this paper, we propose a hydrodynamic evaluation on this total backreaction force for a non-runaway steady-state bubble expansion, which, after evaluated at the wall interface, exactly reproduces the pressure difference $\Delta_\mathrm{wall}[(\bar{\gamma}^2-1)w]$ obtained previously from the junction condition of the total energy-momentum tensor at the wall interface, where $w$ is the enthalpy and $\bar{\gamma}\equiv(1-\bar{v}^2)^{-1/2}$ is the Lorentz factor of the wall-frame fluid velocity $\bar{v}$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Pavan Kumar Aluri
Paolo Cea
Pravabati Chingangbam
Ming-Chung Chu
Roger G. Clowes
Damien Hutsemékers
Joby P. Kochappan
Alexia M. Lopez
Lang Liu
Niels C. M. Martens
C. J. A. P. Martins
Konstantinos Migkas
Eoin Ó Colgáin
Pratyush Pranav
Lior Shamir
Ashok K. Singal
M. M. Sheikh-Jabbari
Jenny Wagner
Shao-Jiang Wang
David L. Wiltshire
摘要： The Cosmological Principle (CP) -- the notion that the Universe is spatially isotropic and homogeneous on large scales -- underlies a century of progress in cosmology. It is conventionally formulated through the Friedmann-Lema\^itre-Robertson-Walker (FLRW) cosmologies as the spacetime metric, and culminates in the successful and highly predictive $\Lambda$-Cold-Dark-Matter ($\Lambda$CDM) model. Yet, tensions have emerged within the $\Lambda$CDM model, most notably a statistically significant discrepancy in the value of the Hubble constant, $H_0$. Since the notion of cosmic expansion determined by a single parameter is intimately tied to the CP, implications of the $H_0$ tension may extend beyond $\Lambda$CDM to the CP itself. This review surveys current observational hints for deviations from the expectations of the CP, highlighting synergies and disagreements that warrant further study. Setting aside the debate about individual large structures, potential deviations from the CP include variations of cosmological parameters on the sky, discrepancies in the cosmic dipoles, and mysterious alignments in quasar polarizations and galaxy spins. While it is possible that a host of observational systematics are impacting results, it is equally plausible that precision cosmology may have outgrown the FLRW paradigm, an extremely pragmatic but non-fundamental symmetry assumption.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The primordial black hole (PBH) productions from the inflationary potential with an inflection point usually rely heavily on the fine-tuning of the model parameters. We propose in this work a new kind of the $\alpha$-attractor inflation with asymmetric double poles that naturally lead to two periods of the standard slow-roll phases connected by a non-attractor ultra-slow-roll phase, during which the PBH productions are guaranteed without fine-tuning the model parameters. This double-pole inflation can be tested against the observational data in the future with rich phenomenological signatures: (1) the enhanced curvature perturbations at small scales admit a distinctive feature of ultraviolet oscillations in the power spectrum; (2) the quasi-monochromatic mass function of the produced PBHs can be made compatible to the asteroid-mass PBHs as the dominant dark matter component, the planet-mass PBHs as the OGLE ultrashort-timescale microlensing events, and the solar-mass PBHs as the LIGO events; (3) the induced gravitational waves can be detected by the gravitational-wave detectors in space and Pulsar Timing Array/Square Kilometer Array.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The stochastic gravitational-wave backgrounds (SGWBs) from the cosmological first-order phase transitions (FOPTs) serve as a promising probe for the new physics beyond the standard model of particle physics. When most of the bubble walls collide with each other long after they had reached the terminal wall velocity, the dominated contribution to the SGWBs comes from the sound waves characterized by the efficiency factor of inserting the released vacuum energy into the bulk fluid motions. However, the previous works of estimating this efficiency factor have only considered the simplified case of the constant sound velocities in both symmetric and broken phases, either for the bag model with equal sound velocities or $\nu$-model with different sound velocities in the symmetric and broken phases, which is unrealistic from a viewpoint of particle physics. In this paper, we propose to solve the fluid EoM with an iteration method when taking into account the sound-velocity variation across the bubble wall for a general and realistic equation of state (EoS) beyond the simple bag model and $\nu$-model. We have found a suppression effect for the efficiency factor of bulk fluid motions, though such a suppression effect could be negligible for the strong FOPT, in which case the previous estimation from a bag EoS on the efficiency factor of bulk fluid motions still works as a good approximation.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Hubble tension seems to be a crisis with $\sim5\sigma$ discrepancy between the most recent local distance ladder measurement from type Ia supernovae calibrated by Cepheids and the global fitting constraint from the cosmic microwave background data. To narrow down the possible late-time solutions to the Hubble tension, we have used in a recent study [Phys. Rev. D 105, L021301 (2022)] an improved inverse distance ladder method calibrated by the absolute measurements of the Hubble expansion rate at high redshifts from the cosmic chronometer data, and found no appealing evidence for new physics at the late time beyond the $\Lambda$CDM model characterized by a parametrization based on the cosmic age. In this paper, we further investigate the perspective of this improved inverse distance ladder method by including the late-time matter perturbation growth data. Independent of the dataset choices, model parametrizations, and diagnostic quantities ($S_8$ and $S_{12}$), the new physics at the late time beyond the $\Lambda$CDM model is strongly disfavored so that the previous late-time no-go guide for the Hubble tension is further strengthened.
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： 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： 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： 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
Ligong Bian
Rong-Gen Cai
Shuo Cao
Zhoujian Cao
He Gao
Zong-Kuan Guo
Kejia Lee
Di Li
Jing Liu
Youjun Lu
Shi Pi
Jian-Min Wang
Shao-Jiang Wang
Yan Wang
Tao Yang
Xing-Yu Yang
Shenghua Yu
Xin Zhang
摘要： It has been a half-decade since the first direct detection of gravitational waves, which signifies the coming of the era of the gravitational-wave astronomy and gravitational-wave cosmology. The increasing number of the detected gravitational-wave events has revealed the promising capability of constraining various aspects of cosmology, astronomy, and gravity. Due to the limited space in this review article, we will briefly summarize the recent progress over the past five years, but with a special focus on some of our own work for the Key Project ``Physics associated with the gravitational waves'' supported by the National Natural Science Foundation of China. In particular, (1) we have presented the mechanism of the gravitational-wave production during some physical processes of the early Universe, such as inflation, preheating and phase transition, and the cosmological implications of gravitational-wave measurements; (2) we have put constraints on the neutron star maximum mass according to GW170817 observations; (3) we have developed a numerical relativity algorithm based on the finite element method and a waveform model for the binary black hole coalescence along an eccentric orbit.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Hubble tension, if not caused by any systematics, could be relieved or even resolved from modifying either the early-time or late-time Universe. The early-time modifications are usually in tension with either galaxy clustering or galaxy lensing constraints. The late-time modifications are also in conflict with the constraint from the inverse distance ladder, which, however, is weakened by the dependence on a sound-horizon prior and some particular approximation for the late-time expansion history. To achieve a more general no-go argument for the late-time scenarios, we propose to use a global parametrizationbased on the cosmic age (PAge) to consistently use the cosmic chronometers data beyond the Taylor expansion domain and without the input of a sound-horizon prior. Both the early-time and late-time scenarios are therefore largely ruled out, indicating the possible ways out of the Hubble tension from either exotic modifications of our concordance Universe or some unaccounted systematics.
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： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The future space-borne gravitational wave (GW) detectors would provide a promising probe for the new physics beyond the standard model that admits the first-order phase transitions. The predictions for the GW background vary sensitively among different concrete particle physics models but also share a large degeneracy in the model buildings, which motivates an effective model description on the phase transition based on different patterns of the electroweak symmetry breaking (EWSB). In this paper, using the scalar $N$-plet model as a demonstration, we propose an effective classification for three different patterns of EWSB: (1) radiative symmetry breaking with classical scale invariance, (2) Higgs mechanism in generic scalar extension, and (3) higher dimensional operators. We conclude that a strong first-order phase transition could be realized for (1) and (2) with a small quartic coupling and a small isospin of an additional $N$-plet field for the light scalar field model with and without the classical scale invariance, and (3) with a large mixing coupling between scalar fields and a large isospin of the $N$-plet field for the heavy scalar field model.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Primordial black holes (PBHs) produced in the early Universe have attracted wide interest for their ability to constitute dark matter and explain the compact binary coalescence. We propose a new mechanism of PBH production during first-order phase transitions (PTs) and find that PBHs are naturally produced during PTs model-independently. Because of the randomness of the quantum tunneling, there always exists some probability that the vacuum decay is postponed in a whole Hubble volume. Since the vacuum energy density remains constant while radiation is quickly redshifted in the expanding Universe, the postponed vacuum decay then results in overdense regions, which finally collapse into PBHs as indicated by numerical simulations. Utilizing this result one can obtain mutual predictions and constraints between PBHs and GWs from PTs. The predicted mass function of PBHs is nearly monochromatic. We investigate two typical cases and find that 1) PBHs from a PT constitute all dark matter and GWs peak at $1$Hz, 2) PBHs from a PT can explain the coalescence events observed by LIGO-Virgo collaboration, and meanwhile GWs can explain the common-spectrum process detected by NANOGrav collaboration.
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