The cosmic microwave background (CMB) temperature, $T$, surely the most precisely measured cosmological parameter, has been inferred from local measurements of the black body spectrum to an exquisite precision of 1 part in $\sim 4700$. On the other hand, current precision allows inference of other basic cosmological parameters at the $\sim 1\%$ level from CMB power spectra, galaxy correlation and lensing, luminosity distance measurements of supernovae, as well as other cosmological probes. A basic consistency check of the standard cosmological model is an independent inference of $T$ at recombination. In this work, we first use the recent Planck data, supplemented by either the first year data release of the dark energy survey, baryon acoustic oscillations (BAO) data, and the Pantheon SNIa (supernovae type Ia) catalog, to extract $T$ at the $\sim 1\%$ precision level. We then explore correlations between $T$, the Hubble parameter, $H_0$, and the global spatial curvature parameter, ${\mathrm{\Omega }}_k$. Our parameter estimation indicates that imposing the local constraint from the SH0ES experiment on $H_0$ results in significant statistical preference for departure at recombination from the locally inferred $T$. However, only moderate evidence is found in this analysis for tension between local and cosmological estimates of $T$, if the local constraint on $H_0$ is relaxed. All other data set combinations that include the CMB with either BAO, SNIa, or both, disfavor the addition of a new free temperature parameter even in the presence of the local constraint on $H_0$. Analysis limited to the Planck data set suggests the temperature at recombination was higher than expected at recombination at the $\gtrsim 95\%$ confidence level if space is globally flat. An intriguing interpretation of our results is that fixing the temperature to its locally inferred value would result in a preference for spatially closed Universe, if $T(z)$ is assumed to evolve adiabatically and the analysis is based only on the Planck data set.

We compute the quantum tunneling rate of dilute axion stars close to the maximum mass [P.H. Chavanis, Phys. Rev. D 84, 043531 (2011)] using the theory of instantons. We confirm that the lifetime of metastable states is extremely long, scaling as $t_{\mathrm{life}}\sim e^N{t}_D$ (except close to the critical point), where $N$ is the number of axions in the system and $t_D$ is the dynamical time ($N\sim {10}^{57}$ and $t_D\sim 10\mathrm{hrs}$ for typical QCD axion stars; $N\sim {10}^{96}$ and $t_D\sim 100\mathrm{Myrs}$ for the quantum core of a dark matter halo made of ultralight axions). Therefore, metastable equilibrium states can be considered as stable equilibrium states in practice. We develop a finite size scaling theory close to the maximum mass and predict that the collapse time at criticality scales as $t_{\mathrm{coll}}\sim N^{1/5}{t}_D$ instead of being infinite when fluctuations are neglected. The collapse time at criticality is smaller than the age of the universe for QCD axion stars and larger than the age of the universe for dark matter cores made of ultralight axions. We also consider the thermal tunneling rate and reach the same conclusions. We compare our results with similar results obtained for Bose-Einstein condensates in laboratory, globular clusters in astrophysics, and quantum field theory in the early Universe.

As the number of gravitational-wave transient detections grows, the inclusion of marginally significant events in gravitational-wave catalogs will lead to increasing contamination from false positives. In this paper, we address the question of how to carry out population studies in light of the fact that some fraction of marginally significant gravitational-wave events are of terrestrial origin. We show that previously published estimates of $p_{\text{astro}}$, the probability that an event is of astrophysical origin, imply an effective noise likelihood, which can be used to take into account the uncertain origin of marginal events in population studies. We derive a formalism to carry out population studies with ambiguous gravitational-wave events. We demonstrate this formalism using events from the LIGO/Virgo Gravitational-Wave Transient Catalog 1 as well as events from the Venumadhav et al. [Phys. Rev. D 101, 083030 (2020).] “IAS Catalog.” We derive posterior distributions for population parameters and discuss how they change when we take into account $p_{\text{astro}}$. We provide updated individual-event posterior distributions by including population information.

Multiparton interactions (MPI) in $pp$ collisions have attracted the attention of the heavy-ion community since they can help to elucidate the origin of collectivelike effects discovered in small collision systems at the LHC. In this work, we report that in pythia8.244, the charged-particle production in events with a large number of MPI (${\mathrm{N}}_{\mathrm{mpi}}$) normalized to that obtained in minimum-bias $pp$ collisions shows interesting features. After the normalization to the corresponding $⟨{\mathrm{N}}_{\mathrm{mpi}}⟩$, the ratios as a function of $p_{\mathrm{T}}$ exhibit a bump at $p_{\mathrm{T}}\approx 3\mathrm{GeV}/c$; and for higher $p_{\mathrm{T}}$ ($>8\mathrm{GeV}/c$), the ratios are independent of ${\mathrm{N}}_{\mathrm{mpi}}$. While the size of the bump increases with increasing ${\mathrm{N}}_{\mathrm{mpi}}$, the behavior at high $p_{\mathrm{T}}$ is expected from the “binary scaling” (parton-parton interactions), which holds given the absence of any parton-energy loss mechanism in pythia. The bump at intermediate $p_{\mathrm{T}}$ is reminiscent of the Cronin effect observed for the nuclear modification factor in $p$-Pb collisions. In order to unveil these effects in data, we propose a strategy to construct an event classifier sensitive to MPI using machine learning-based regression. The study is conducted using TMVA, and the regression is performed with boosted decision trees (BDT). Event properties like forward charged-particle multiplicity, transverse spherocity and the average transverse momentum ($⟨p_{\mathrm{T}}⟩$) are used for training. The kinematic cuts are defined in accordance with the ALICE detector capabilities. For the validation of the method and to find possible model dependence, we also compare the results from pythia8.244 with herwig7.1. In addition, we also report that if we apply the trained BDT on existing ($\mathrm{INEL}>0$) $pp$ data, i.e., events with at least one primary charged-particle within $|\eta |<1$, the average number of MPI in $pp$ collisions at $\sqrt{s}=5.02$ and 13 TeV are $3.76\pm 1.01$ and $4.65\pm 1.01$, respectively.

Current LHC searches for nonsupersymmetric singly charged scalars, based on two-Higgs-doublet models, in general, focus the analysis in third-generation fermions in the final state. However, singly charged scalars in alternative extensions of the scalar sector involve Yukawa couplings not proportional to the mass of the fermions. Assuming the scalar decays into electrons and muons, it can manifest cleaner experimental signatures. In this paper, we suggest that a singly charged scalar singlet, with electroweak production, can start to be probed in the near future with dedicated search strategies. Depending on the strength of the Yukawa couplings, two independent scenarios are considered: direct pair production (small couplings) and single production via a virtual neutrino exchange (large couplings). We show that, up to a mass as large as 500 GeV, most of the parameter space could be excluded at the 95% C.L. in a high-luminosity phase of the LHC. Our results also apply to other frameworks, provided the singly charged scalar exhibits similar production patterns and dominant decay modes.

We analyze $CP$-violating effects in both electric dipole moment (EDM) measurements and future analyses at the Large Hadron Collider (LHC) assuming a two-Higgs-doublet model (2HDM) with “soft” $CP$ violation. Our analysis of EDMs and current LHC constraints shows that, in the case of Type II and Type III 2HDMs, an $\mathcal{O}(0.1)$ $CP$-violating phase in the Yukawa interaction between $H_1$ (the 125 GeV Higgs boson) and fermions is still allowed. For these scenarios, we study $CP$-violating effects in the neutron EDM and $t\overline{t}{H}_1$ production at the LHC. Our analysis shows that such an $\mathcal{O}(0.1)$ $CP$-violating phase can be easily confirmed or excluded by future neutron EDM tests, with LHC data providing a complementary cross-check.

We propose a novel dark matter (DM) scenario based on a first-order phase transition in the early Universe. If dark fermions acquire a huge mass gap between true and false vacua, they can barely penetrate into the new phase. Instead, they get trapped in the old phase and accumulate to form macroscopic objects, dubbed Fermi-balls. We show that Fermi-balls can explain the DM abundance in a wide range of models and parameter space, depending most crucially on the dark-fermion asymmetry and the phase transition energy scale (possible up to the Planck scale). They are stable by the balance between fermion’s quantum pressure against free energy release, hence turn out to be macroscopic in mass and size. However, this scenario generally produces no detectable signals (which may explain the null results of DM searches), except for detectable gravitational waves for electroweak scale phase transitions; although the detection of such stochastic gravitational waves does not necessarily imply a Fermi-ball DM scenario.

One- and two-zero textures for the flavor neutrino mass matrix have been successful in explaining mixing in the neutrino sector. Conservatively, six cases of one-zero textures and seven cases of two-zero textures are compatible with observations. We show that one case may be the most natural in the one- and two-zero textures schemes if tiny neutrino masses are generated by the type-II seesaw mechanism in triplet Higgs models.

A lattice QCD approach to quark orbital angular momentum in the proton based on generalized transverse momentum-dependent parton distributions (GTMDs) is enhanced methodologically by incorporating a direct derivative technique. This improvement removes a significant numerical bias that had been seen to afflict results of a previous study. In particular, the value obtained for Ji quark orbital angular momentum is reconciled with the one obtained independently via Ji’s sum rule, validating the GMTD approach. Since GTMDs simultaneously contain information about the quark impact parameter and transverse momentum, they permit a direct evaluation of the cross product of the latter. They are defined through proton matrix elements of a quark bilocal operator containing a Wilson line; the choice in Wilson line path allows one to continuously interpolate from Ji to Jaffe-Manohar quark orbital angular momentum. The latter is seen to be significantly enhanced in magnitude compared to Ji quark orbital angular momentum, confirming previous results.

We present a calculation of $P\to {\gamma }^{(*)}{\gamma }^{(*)}$ processes, where $P={\pi }^0,\eta ,{\eta }^{\prime }$, at the one-loop level up to and including next-to-next-to-leading order (NNLO) in large-$N_c$ chiral perturbation theory. The results are numerically evaluated successively at LO, NLO, and NNLO. The appearing low-energy constants are determined through fits to the available experimental data. We investigate the decay widths to real photons, the single-virtual transition form factors, and the widths of $P\to \gamma l^{+}{l}^{-}$, where $l=e$, $\mu$. Furthermore, we provide results for the slopes and curvatures of the transition form factors.

The cross section for coherent elastic neutrino-nucleus scattering ($\mathrm{CE}\nu \mathrm{NS}$) depends on the response of the target nucleus to the external current, in the Standard Model (SM) mediated by the exchange of a $Z$ boson. This is typically subsumed into an object called the weak form factor of the nucleus. Here, we provide results for this form factor calculated using the large-scale nuclear shell model for a wide range of nuclei of relevance for current $\mathrm{CE}\nu \mathrm{NS}$ experiments, including cesium, iodine, argon, fluorine, sodium, germanium, and xenon. In addition, we provide the responses needed to capture the axial-vector part of the cross section, which does not scale coherently with the number of neutrons, but may become relevant for the SM prediction of $\mathrm{CE}\nu \mathrm{NS}$ on target nuclei with nonzero spin. We then generalize the formalism allowing for contributions beyond the SM. In particular, we stress that in this case, even for vector and axial-vector operators, the standard weak form factor does not apply anymore, but needs to be replaced by the appropriate combination of the underlying nuclear structure factors. We provide the corresponding expressions for vector, axial-vector, but also (pseudo)scalar, tensor, and dipole effective operators, including two-body-current effects as predicted from chiral effective field theory (EFT). Finally, we update the spin-dependent structure factors for dark matter scattering off nuclei according to our improved treatment of the axial-vector responses.

Initial conditions for relativistic heavy-ion collisions may be far from equilibrium (i.e., there are large initial contributions from the shear-stress tensor and bulk pressure), but it is expected that on very short timescales the dynamics converge to a universal attractor that defines hydrodynamic behavior. Thus far, studies of this nature have only considered an idealized situation at LHC energies (high temperatures $T$ and vanishing baryon chemical potential ${\mu }_B=0$), but in this work, we investigate for the first time how far-from-equilibrium effects may influence experimentally driven searches for the quantum chromodynamic critical point at the Relativistic Heavy Ion Collider. We find that the path to the critical point is heavily influenced by far-from-equilibrium initial conditions where viscous effects lead to dramatically different $\{T,{\mu }_B\}$ trajectories through the QCD phase diagram. We compare hydrodynamic equations of motion with shear and bulk coupled together at finite ${\mu }_B$ for both Denicol-Niemi-Molnar-Rischke and phenomenological Israel-Stewart equations of motion and discuss their influence on potential attractors at finite ${\mu }_B$ and their corresponding $\{T,{\mu }_B\}$ trajectories.

Onset of chaos for the holographic dual of a $Q\overline{Q}$ system at finite temperature and baryon density is studied. We consider a string in the AdS Reissner–Nordstrom background near the black-hole horizon and investigate small time-dependent perturbations of the static configurations. The proximity to the horizon induces chaos, which is softened increasing the chemical potential. A background geometry including the effect of a dilaton is also examined. The Maldacena, Shenker, and Stanford bound on the Lyapunov exponents characterizing the perturbations is satisfied for finite baryon chemical potential and when the dilaton is included in the metric.

This paper revives the controversial debate that has arisen over the last two decades about the possibility that the electromagnetic field affects the lifetime or the decay rate of an unstable particle. In this research, we show, by performing analytical calculations and extracting numerical results, that the pion lifetime can be changed notably by inserting the decaying pion into an electromagnetic field only if the number of photons transferred between the decaying system and the laser field does not reach the well-known sum rule. The influence of the laser parameters on the decay rate and branching ratio is also discussed. The surprising result obtained for the pion lifetime is referred to as the well-known quantum Zeno effect.

We study the effect of magnetic field on heavy quark-antiquark pair in both Einstein-Maxwell (EM) and Einstein-Maxwell-dilaton (EMD) model. The interquark distance, free energy, entropy, binding energy, and internal energy of the heavy quarkonium are calculated. It is found that the free energy suppresses and the entropy increases quickly with the increase of the magnetic field $B$. The binding energy vanishes at smaller distance when increasing the magnetic field, which indicates the quark-antiquark pair dissociates at smaller distance. The internal energy which consists of free energy and entropy will increase at large separating distance for a nonvanishing magnetic field. These conclusions are consistent both in the EM and EMD model. Moreover, we also find that the quarkonium will dissociate easier in the parallel direction than that in the transverse direction for EMD model, but the conclusion is opposite in EM model. Lattice results are in favor of EMD model. Besides, a Coulomb-plus-linear potential (Cornell potential) can be realized only in EMD model. Thus, a dilaton field is proved to be important in holographic model. Finally, we also show that the free energy, entropy, and internal energy of a single quark in EMD model with the presence of magnetic field.

Recently it was shown that the scaling dimension of the operator ${\varphi }^n$ in scale invariant $d=3$ theory may be computed semiclassically, and this was verified to leading order (two loops) in perturbation theory at leading and subleading $n$. Here we extend this verification to six loops, once again at leading and subleading $n$. We then perform a similar exercise for a theory with a multiplet of real scalars and an $O(N)$ invariant hexic interaction. We also investigate the strong-coupling regime for this example.

I derive a universal factor accounting for the soft axion radiation in the zero frequency limit, dressing any differential cross sections for arbitrary multifermion collisions. The universal soft expression can be factorized from the bare differential cross sections of hard emissions. The soft factorization accounts for all leading-order $O({\omega }^2)$ contributions of the soft axion bremsstrahlung. Intriguingly, despite completely different physical origins, we find many similarities with the $O({\omega }^2)$ radiation in gravity, from the subsubleading soft graviton theorem.

The aftermath of binary black hole coalescence is a perturbed remnant whose gravitational radiation rings down, encoding information about the new black hole’s recent history and current state. It is expected that this ringdown radiation will be composed primarily of Kerr quasinormal modes, and thereby enable tests of general relativity. Here, the first complete ringdown signal model for nonprecessing binary black hole systems is presented: multipole amplitudes and phases are modeled as functions of initial binary parameters. It is found that using the peak time of the dominant merger multipole as a reference results in the dominant mode’s excitation being a remarkably simple linear function of system parameters, strongly suggesting that an analytic treatment may be within reach. In particular, for initially nonspinning black holes, the dominant quadrupole is excited as $-4$ times the system’s symmetric mass ratio. Application of the model to parameter estimation allows general relativity predictions for mode amplitudes independently of signal strength. Treatment of GW150914 indicates some mode amplitudes and relative phases are intrinsically difficult to constrain.

We derive the Boltzmann equation in the context of a gravity theory with nonminimal coupling between matter and curvature. We show that as the energy-momentum tensor is not conserved in these theories, it follows a condition on the normalization of a homogeneous distribution function. The Boltzmann H-theorem is preserved such that the entropy vector flux is still a nondecreasing function in these theories. The case of a homogeneous and isotropic universe is analyzed.

We complete our previous derivation, at the sixth post-Newtonian (6PN) accuracy, of the local-in-time dynamics of a gravitationally interacting two-body system by giving two gauge-invariant characterizations of its complementary nonlocal-in-time dynamics. On the one hand, we compute the nonlocal part of the scattering angle for hyberboliclike motions; and, on the other hand, we compute the nonlocal part of the averaged (Delaunay) Hamiltonian for ellipticlike motions. The former is computed as a large-angular-momentum expansion (given here to next-to-next-to-leading order), while the latter is given as a small-eccentricity expansion (given here to the tenth order). We note the appearance of $\zeta (3)$ in the nonlocal part of the scattering angle. The averaged Hamiltonian for ellipticlike motions then yields two more gauge-invariant observables: the energy and the periastron precession as functions of orbital frequencies. We point out the existence of a hidden simplicity in the mass-ratio dependence of the gravitational-wave energy loss of a two-body system. We include a Supplemental Material that gives the explicit analytic form of a scattering integral which we could only evaluate numerically.