For primordial black holes (PBHs) to form a considerable fraction of cold dark matter, the required amplitude of primordial scalar perturbations is quite large ($P_{\zeta }(k)\sim {10}^{-2}$) if PBH is formed in radiation epoch. In alternate cosmological histories, where additional epoch of arbitrary equation of state precede radiation epoch, the dynamics of PBH formation and relevant mass ranges can be different leading to lower requirement of primordial power at smaller scales of inflation. Moreover, this alternate history can modify the predictions for the gravitational wave (GW) spectrum, which can be probed by upcoming GW observations. In this paper we show that an early kination epoch can lead to percent level abundance of PBH for a lower amplitude of $P_{\zeta }(k)$ as compared to PBH formation in a standard radiation epoch. Moreover, we calculate the effect of early kination epoch on the GW spectrum for first and second orders in perturbation theory which show enhancement in the amplitude of the GW spectrum in a kination epoch with respect to that in a standard radiation epoch.

The first-order relativistic fluid theories of dissipation proposed by Eckart and Landau-Lifshitz have been proved to be unstable. They admit solutions which start in proximity of equilibrium and depart exponentially from it. We show that this behavior is due to the fact that the total entropy of these fluids, restricted to the dynamically accessible states, has no upper bound. As a result, these systems have the tendency to constantly change according to the second law of thermodynamics and the unstable modes represent the directions of growth of the entropy in state space. We, then, verify that the conditions of stability of Israel and Stewart’s theory are exactly the requirements for the entropy to have an absolute maximum. Hence, we explain how the instability of the first-order theories is a direct consequence of the truncation of the entropy current at the first order, which turns the maximum into a saddle point of the total entropy. Finally, we show that recently proposed first-order stable theories, constructed using more general frames, do not solve the instability problem by providing a maximum for the entropy, but, rather, are made stable by allowing for small violations of the second law.

Because of the long-range nature of the gravitational interaction, self-gravitating systems never reach thermal equilibrium in the thermodynamic limit but remain trapped in nonequilibrium stationary states, or quasiequilibrium states. Here, we deal with quasiequilibrium self-gravitating systems by representing them as a collection of smaller subsystems that remain infinitely close to equilibrium. These subsystems represent regions from where thermalization spreads later over the whole system. Such a methodological attitude allows representing their statistical properties as a superposition of statistics, i.e., superstatistics. It has the advantage of producing Tsallis distributions, widely used in fitting observational data, as a special case of a more general family of distributions, while relying only on conventional statistical mechanics. Focusing on the three universality classes of superstatistics, namely, ${\chi }^2$, inverse-${\chi }^2$, and log-normal superstatistics, we discuss the velocity distributions arising in this picture and confront them with independent numerical simulations. Then, we study the consequences on typical phenomena arising in self-gravitating systems. We discuss the Jeans instability in the classical regime, for a static and an expanding universe, and extend our results to the quantum regime by applying the Wigner-Moyal procedure. Our results reveal that quasiequilibrium systems remain stable for larger perturbations, as compared to equilibrium systems, meaning that a larger mass is needed to initiate the gravitational collapse. This is particularly relevant for Bok globules because their mass is of the same order as their Jeans mass; hence, a small deviation from equilibrium may lead to a different prediction for their stability. We also discuss the Chandrasekhar dynamical friction in a quasiequilibrium medium and analyze the consequences on the decay of globular orbits. Our results suggest that the superstatistical picture may offer a partial solution to the problem of the large timescales shown by numerical $N$-body simulations and semianalytical models.

Nuclear shadowing corrections to the structure functions of deep inelastic scattering on intermediate-mass nuclei are calculated at very small values of Bjorken $x$ and small values of $Q^2$ $(Q^2\le 5{\mathrm{GeV}}^2)$. The two-component approach developed in previous works of authors for a description of the nucleon structure functions of deep inelastic scattering is used. It is shown that the hard component of the nucleon structure functions that arises, in terms of the color dipole model, from $q\overline{q}$-pairs with a high transverse momentum, is almost not shadowed. It is shown that a change of the slope of the shadowing curve with a decrease of $x$ depends, at small values of $x$, on the relative contribution of the hard component to the nucleon structure function (this contribution is a function of $x$ and $Q^2$) and on a size of gluon saturation effects. It is shown that an accounting for saturation effects becomes essential for predictions of shadowing at $x<({10}^{-5}–{10}^{-4})$, depending on a value of $Q^2$. Results of numerical calculations of nuclear shadowing for several nuclei are compared with available data of the E665 and the NMC Collaborations.

We study the matter effect caused by nonstandard neutrino interactions (NSI) in the future solar neutrino experiments, DUNE, HK, and MICA. The upcoming reactor experiment, JUNO is expected to provide the most precise measurements of solar neutrino oscillation parameters and is going to open up the era of subpercent precision in the leptonic mixing sector of the Standard Model (SM). Assuming JUNO can measure $\mathrm{\Delta }{m}_{21}^2$ and ${\mathrm{\Theta }}_{12}$ by subpercent precision and assuming SM as the null hypothesis, we study the possibility to constrain NSI parameters by the future solar neutrino experiments such as DUNE, HK and MICA and present excluded region in NSI parameter space, ${\epsilon }_N$ and ${\epsilon }_D$. For this purpose, we study the effect of NSI on solar neutrino propagation in the Sun and Earth and explore the dependence of the day-night asymmetry on the NSI parameters. we also study the effect of NSI at the detector on the simulated data for these experiments.

We report the results of a lattice quantum chromodynamics calculation of $F_K/F_{\pi }$ using Möbius domain-wall fermions computed on gradient-flowed $N_f=2+1+1$ highly improved staggered quark (HISQ) ensembles. The calculation is performed with five values of the pion mass ranging from $130\lesssim m_{\pi }\lesssim 400\mathrm{MeV}$, four lattice spacings of $a\sim 0.15$, 0.12, 0.09 and 0.06 fm and multiple values of the lattice volume. The interpolation/extrapolation to the physical pion and kaon mass point, the continuum, and infinite volume limits are performed with a variety of different extrapolation functions utilizing both the relevant mixed-action effective field theory expressions as well as discretization-enhanced continuum chiral perturbation theory formulas. We find that the $a\sim 0.06\mathrm{fm}$ ensemble is helpful, but not necessary to achieve a subpercent determination of $F_K/F_{\pi }$. We also include an estimate of the strong isospin breaking corrections and arrive at a final result of $F_{{\widehat{K}}^{+}}/F_{{\widehat{\pi }}^{+}}=1.1942(45)$ with all sources of statistical and systematic uncertainty included. This is consistent with the Flavour Lattice Averaging Group average value, providing an important benchmark for our lattice action. Combining our result with experimental measurements of the pion and kaon leptonic decays leads to a determination of $|V_{us}|/|V_{ud}|=0.2311(10)$.

In the present work, the partial decay widths of $P_c(4312)$ to ${\eta }_{c}p$ and $J/\psi p$ are investigated with the QCD sum rule method under the assumption that $P_c(4312)$ is a $\overline{D}{\mathrm{\Sigma }}_c$ molecular state with $J^P={\frac{1}{2}}^{-}$. In the analysis, the pole residue of $P_c(4312)$, one of the input parameters for the calculations of the strong decay constants, is calculated first. With the numerical values of the strong decay constants, the partial decay widths to ${\eta }_{c}p$ and $J/\psi p$ are estimated to be $\mathrm{\Gamma }(P_c(4312)\to {\eta }_{c}p)=5.54_{-0.5}^{+0.75}\mathrm{MeV}$ and $\mathrm{\Gamma }(P_c(4312)\to J/\psi p)=1.67_{-0.56}^{+0.92}\mathrm{MeV}$, respectively, which are compatible with the measured total width of $P_c(4312)$. The results suggest that it is reasonable to assign $P_c(4312)$ to be a $\overline{D}{\mathrm{\Sigma }}_c$ molecular state with $J^P={\frac{1}{2}}^{-}$.

We discuss the QCD phase structure at finite temperature and chemical potential for 2-flavor and $2+1$-flavor QCD. The results are achieved by computing QCD correlation functions within a generalized functional approach that combines Dyson-Schwinger equations (DSE) and the functional renormalization group (fRG). In this setup fRG precision data from [A. K. Cyrol, M. Mitter, J. M. Pawlowski, and N. Strodthoff, Phys. Rev. D 97, 054006 (2018).] for the vacuum quark-gluon vertex and gluon propagator of 2-flavor QCD used as input, and the respective DSEs are expanded about this input. While the vacuum results for other correlation functions serve as a self-consistency check for functional approaches, the results at finite temperature and density are computed, for the first time, without the need of phenomenological infrared parameters.

The scalar and vector meson exchange contributions to the doubly radiative decays ${\eta }^{(\prime )}\to {\pi }^0\gamma \gamma$ and ${\eta }^{\prime }\to \eta \gamma \gamma$ are analyzed within the linear sigma model and vector meson dominance frameworks, respectively. Predictions for the diphoton invariant mass spectra and the associated integrated branching ratios are given and compared with current available experimental data. While a satisfactory description of the shape of the $\eta \to {\pi }^0\gamma \gamma$ and ${\eta }^{\prime }\to {\pi }^0\gamma \gamma$ decay spectra is obtained, thus supporting the validity of the approach, the corresponding branching ratios cannot be reproduced simultaneously. A first theoretical prediction for the recently measured ${\eta }^{\prime }\to \eta \gamma \gamma$ by the BESIII Collaboration is also presented.

We investigate possible renormalization-group fixed points at nonzero coupling in ${\varphi }^3$ theories in six spacetime dimensions, using beta functions calculated to the four-loop level. We analyze three theories of this type, with (a) a one-component scalar, (b) a scalar transforming as the fundamental representation of a global $\mathrm{SU}(N)$ symmetry group, and (c) a scalar transforming as a bi-adjoint representation of a global $\mathrm{SU}(N)\otimes \mathrm{SU}(N)$ symmetry. We do not find robust evidence for such fixed points in theories (a) or (b). Theory (c) has the special feature that the one-loop term in the beta function is zero; implications of this are discussed.

Standard sirens have been proposed as probes of alternative theories of gravity, such as Horndeski models. Hitherto, all studies have been conducted on a homogeneous-isotropic cosmological background, which is unable to consistently account for realistic distributions of matter, and for inhomogeneities in the Horndeski scalar field. Yet, the latter are essential for screening mechanisms. In this article, we comprehensively analyze the propagation of Horndeski gravitational waves in an arbitrary background spacetime and scalar field. We restrict our study to the class of theories in which gravitational waves propagate at light speed, we work in the geometric-optics regime, and we neglect scalar radiation. We find that kinetic braiding produces a nonphysical longitudinal mode, whereas conformal coupling affects the amplitude of the standard transverse modes but not their polarization. We confirm that any observable deviation from general relativity depends on the local value of the effective Planck mass at emission and reception of the wave. This result is interpreted as the conservation of the number of gravitons.

Kachru-Kallosh-Linde-Trivedi (KKLT) scenario has succeeded in stabilizing the volume modulus and constructing metastable de Sitter (dS) vacua in type IIB string theory. We revisit to investigate the possibility of the oscillon (or I-ball) formation in the KKLT scenario when the volume modulus is initially displaced from the dS minimum. Special attention is paid to physically realistic initial conditions of the volume modulus, which was not taken in the literature. Using lattice simulations, we find that oscillons do not form unless the volume modulus is initially placed at very near the local maximum, which requires severe fine-tuning.

We apply a recently proposed cross-correlation power spectrum technique to study relationship between the ultrahigh energy cosmic ray (UHECR) flux from the Pierre Auger Observatory and galaxies from the 2MASS Redshift Survey. Using a simple linear bias model relative to the galaxy auto power spectrum, we are able to constrain the value of bias to be less than 1% for UHECR with energies 4–8 EeV, less than 2.3% for UHECR with energies above 8 EeV and less than 21% for UHECR with energies above 52 EeV (all 95% confidence limit). We study energy dependence of the bias, but the small sample size does not allow us to reach any statistically significant conclusions. For the cosmic ray events above 52 EeV, we discover a curious excess cross-correlation at $\sim 1°$ degree scales. Given similar cross-correlation is not visible at larger angular scales, statistical fluctuation seems like the most plausible explanation.

We elucidate a magnetic mass effect on a sphaleron energy that is crucial for baryon number preservation needed for successful electroweak baryogenesis. We find that the sphaleron energy increases in response to the magnetic mass. As an application, we study the sphaleron energy and electroweak phase transition with the magnetic mass in a two-Higgs-doublet model. Although the magnetic mass can screen the gauge boson loops, it relaxes a baryon number preservation criterion more effectively, broadening the baryogenesis-possible region. Our findings would be universal in any new physics models as long as the gauge sector is common to the standard model.

The spectra and correlation of identical particles emitted from small local-equilibrium sources are considered. The size of the system is defined by the negative part of the parabolic falling chemical potential. The analytical solution of the problem is found for the case of inclusive measurements. It is shown that in the case where the size of the system is comparable to the thermal wavelength of the particles, the spectra and correlation functions are far from the quasiclassical approximation expected for large systems, and observed femtoscopy scales (interferometry radii) will be essentially smaller than the Gaussian radii of the source. If the maximum value of the chemical potential approaches the critical one, specific for the system, one can consider the possibility of Bose-Einstein condensation. In such a case, the reduction of the intercept of the correlation function for inclusive measurements takes place. The results can be used for the searching of femtoscopy homogeneity lengths in proton-proton collisions at LHC energies.

In general two-Higgs-doublet models (2HDMs) without scalar flavor changing neutral couplings (SFCNC) in the lepton sector, the electron, muon, and tau interactions can be decoupled in a robust framework, stable under renormalization group evolution. In this framework, the breaking of lepton flavor universality (LFU) goes beyond the mass proportionality, opening the possibility to accommodate in a simple manner a different behavior among charged leptons. We analyze simultaneously the electron and muon ($g-2$) anomalies in the context of these general flavor conserving models in the leptonic sector ($\mathrm{g}\ell \mathrm{FC}$). We consider two different models, $\mathrm{I}\text{−}\mathrm{g}\ell \mathrm{FC}$ and $\mathrm{I}\mathrm{I}\text{−}\mathrm{g}\ell \mathrm{FC}$, in which the quark Yukawa couplings coincide, respectively, with the ones in type I and in type II 2HDMs. We find two types of solutions that fully reproduce both ($g-2$) anomalies, and which are compatible with experimental constraints from LEP and LHC, from LFU, from flavor and electroweak physics, and with theoretical constraints in the scalar sector. In the first type of solution, all the new scalars have masses in the 1–2.5 TeV range, the vacuum expectation values (vevs) of both doublets are quite similar in magnitude, and both anomalies are dominated by two loop Barr-Zee contributions. This solution appears in both models. There is a second type of solution, where one loop contributions are dominant in the muon anomaly, all new scalars have masses below 1 TeV, and the ratio of vevs is in the range 10–100. The second neutral scalar H is the lighter among the new scalars, with a mass in the 210–390 GeV range while the pseudoscalar A is the heavier, with a mass in the range 400–900 GeV. The new charged scalar ${\mathrm{H}}^{\pm }$ is almost degenerate either with the scalar or with the pseudoscalar. This second type of solution only appears in the $\mathrm{I}\text{−}\mathrm{g}\ell \mathrm{FC}$ model. Both solutions require the soft breaking of the ${\mathbb{Z}}_2$ symmetry of the Higgs potential.

At very high transverse momenta, the dominant mechanism for heavy hadron production is fragmentation. In this work, we first use the nonrelativistic quark model to compute the heavy baryon fragmentation functions at lowest order of perturbative QCD and then we apply the approximative quark-diquark model for the same fragmentation process. Diquark model enables one to analyze the two-stage fragmentation of a heavy quark into a heavy diquark followed by the fragmentation of produced diquark into outgoing heavy baryon. An acceptable agreement is found between the results obtained through both approaches. Relying on the diquark model, we extend our computation to next-to-leading order accuracy at perturbative QCD.

We study the impact of a finite magnetic field on the deconfinement phase transition for heavy quarks by computing the fluctuations of the Polyakov loops. It is demonstrated that the explicit Z(3) breaking field increases with the magnetic field, leading to a decrease in the (pseudo) critical temperatures and a shrinking first-order region in the phase diagram. Phenomenological equations which capture the behaviors of the Z(3) breaking field at strong and weak magnetic fields for massive and massless quarks are given. Lastly, we explore the case of dynamical light quarks, and demonstrate how an improved constituent quark mass function can enforce the correct magnetic field dependence of the deconfinement temperature in an effective model, as observed in Lattice QCD calculations.

We critically (re)examine the associated production process of a $J/\psi$ meson plus an open charm hadron at the LHC in the proton-proton ($pp$) and proton-lead ($p\mathrm{Pb}$) collisions. Such a process is very intriguing in the sense of tailoring to explore the double parton structure of nucleons and to determine the geometry of partons in nuclei. In order to interpret the existing $pp$ data with the LHCb detector at the center-of-mass energy $\sqrt{s}=7\mathrm{TeV}$, we introduce two overlooked mechanisms for the double parton scattering (DPS) and single parton scattering (SPS) processes. Besides the conventional DPS mode, where the two mesons are produced almost independently in the two separate scattering subprocesses, we propose a novel DPS mechanism that the two constituent (heavy) quarks stemming from two hard scatterings can form into a composite particle, like the $J/\psi$ meson, during the hadronization phase. It yields a strong correlation in the final state from the two distinct scattering subprocesses per hadron-hadron collision. Such a mechanism should be ubiquitous for quarkonium associated production processes involving more-than-one pair of same-flavor heavy quarks. However, it turns out the corresponding contribution is small in $J/\psi +c\overline{c}$ hadroproduction. On the contrary, we point out that the resummation of the initial state logarithms due to gluon splitting into a charm quark pair is crucial to understand the LHCb measurement, which was overlooked in the literature. We perform a proper matching between the perturbative calculations in different initial-quark flavor number schemes, generically referring to the variable flavor number scheme. The new variable flavor number scheme calculation for the process strongly enhances the SPS cross sections, almost closing the discrepancies between theory and experiment. Finally, we present our predictions for the forthcoming LHCb measurement in $p\mathrm{Pb}$ collisions at $\sqrt{s_{NN}}=8.16\mathrm{TeV}$. Some interesting observables are exploited to set up the control regions of the DPS signal and to probe the impact-parameter-dependent parton densities in lead.