We investigate spin-0 and spin-$\frac{1}{2}$ perturbations for nonextremal and extremal Reissner-Nordström backgrounds using the isomonodromic method. We calculate the fundamental quasinormal modes (QNMs) associated with each perturbation as a function of the electromagnetic coupling $qQ$ and ratio $Q/M$. After corroborating the literature values for generic $qQ$ and $Q/M$, we turn to study the near-extremal limit. In parallel with the study of QNMs for the Kerr geometry, we find the existence of “nondamping” modes for $qQ$ above a spin-dependent critical value and locate the bifurcation point in the $q-Q$ parameter space.

Gravitational waves from the coalescence of binary black holes can be distinguished from noise transients in a detector network through Bayesian model selection by exploiting the coherence of the signal across the network. We present a Bayesian framework for calculating the posterior probability that a signal is of astrophysical origin, agnostic to the specific search strategy, pipeline or search domain with which a candidate is identified. We apply this framework under identical assumptions to all events reported in the LIGO-Virgo GWTC-1 catalog, GW190412 and numerous event candidates reported by independent search pipelines by other authors. With the exception of GW170818, we find that all GWTC-1 candidates, and GW190412, have odds overwhelmingly in favor of the astrophysical hypothesis, including GW170729, which was assigned significantly different astrophysical probabilities by the different search pipelines used in GWTC-1. GW170818 is de facto a single detector trigger, and is therefore of no surprise that it is disfavored as being produced by an astrophysical source in our framework. We find three additional event candidates, GW170121, GW170425 and GW170727, that have significant support for the astrophysical hypothesis, with a probability that the signal is of astrophysical origin of 0.53, 0.74 and 0.64, respectively. We carry out a hierarchical population study which includes these three events in addition to those reported in GWTC-1, finding that the main astrophysical results are unaffected.

We show that the equation of motion of scalar-tensor theory acquires thermodynamic identity when projected on a generic null surface. The relevant projection is given by $E_{ab}{l}^a{k}^b$, where $E_{ab}=8\pi T_{ab}^{(m)}$ represents the equation of motion for a gravitational field in the presence of external matter, $l^a$ is the generator of the null surface, and $k^a$ is the corresponding auxiliary null vector. Our analysis is done completely in a covariant way. Therefore all the thermodynamic quantities are in covariant form and hence can be used for any specific form of metric adapted to a null surface. We show this both in Einstein and Jordan frames and find that these two frames provide equivalent thermodynamic quantities. This is consistent with the previous findings for a Killing horizon. Also, a concrete proof of the zeroth law in scalar-tensor theory is provided when the null surface is defined by a Killing vector.

We discuss and expand a new approach to the thermodynamics of scalar-tensor gravity and its diffusion toward general relativity (seen as an equilibrium state) proposed in a previous paper [Phys. Rev. D 103, L121501 (2021), upon which we build. We describe scalar-tensor gravity as an effective dissipative fluid and apply Eckart’s first order thermodynamics to it, obtaining explicitly effective quantities such as heat flux, “temperature of gravity,” viscosities, entropy density, plus an equation describing the “diffusion” to Einstein gravity. These quantities, still missing in the usual thermodynamics of spacetime, are obtained with minimal assumptions. Furthermore, we examine certain exact solutions of scalar-tensor gravity to test the proposed formalism and gain some physical insight on the “approach to equilibrium” for this class of theories.

We study the gravitational radiation produced by the collisions of bubble walls or thin fluid shells in cosmological phase transitions. Using the so-called envelope approximation, we obtain analytically the asymptotic behavior of the gravitational wave spectrum at low and high frequencies for any phase transition model. The complete spectrum can thus be approximated by a simple interpolation between these asymptotes. We verify this approximation with specific examples. We use these results to discuss the dependence of the spectrum on the time and size scales of the source.

We provide a formula for estimating the redshift and its secular change (redshift drift) in Lemaître-Tolman-Bondi (LTB) spherically symmetric universes. We compute the scaling of the redshift drift for LTB models that predict Hubble diagrams indistinguishable from those of the standard cosmological model, the flat lambda cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) model. We show that the redshift drift for these degenerate LTB models is typically different from that predicted in the $\mathrm{\Lambda }\mathrm{CDM}$ scenario. We also highlight and discuss some unconventional redshift-drift signals that arise in LTB universes and give them distinctive features compared to the standard model. We argue that the redshift drift is a metric observable that allows us to reduce the degrees of freedom of spherically symmetric models and to make them more predictive and thus falsifiable.

In the $\mathrm{\Lambda }\mathrm{CDM}$ model, cosmological observations from the late and recent Universe reveal a puzzling $\sim 4.5\sigma$ tension in the current rate of Universe expansion. In addition to the various scenarios suggested to resolve the tension, a nonparametric modeling may provide useful insights. In this paper, we look at three well-known nonparametric methods: the smoothing method, the genetic algorithm, and the Gaussian process. Considering these three methods, we employ the recent Hubble parameter data to reconstruct the rate of Universe expansion and supernovae Pantheon sample to reconstruct the luminosity distance. In contrast to similar studies in the literature, the chi-squared distribution has been used to construct a reliable criterion to select a reconstruction. Finally, we compute the current rate of Universe expansion ($H_0$) for each method, provide some discussions regarding the performance of each approach, and compare the results.

Collective neutrino oscillations can potentially play an important role in transporting lepton flavor in astrophysical scenarios where the neutrino density is large, typical examples are the early universe and supernova explosions. It has been argued in the past that simple models of the neutrino Hamiltonian designed to describe forward scattering can support substantial flavor evolution on very short timescales $t\approx \log (N)/(G_F{\rho }_{\nu })$, with $N$ the number of neutrinos, $G_F$ the Fermi constant and ${\rho }_{\nu }$ the neutrino density. This finding is in tension with results for similar but exactly solvable models for which $t\approx \sqrt{N}/(G_F{\rho }_{\nu })$ instead. In this work we provide a coherent explanation of this tension in terms of dynamical phase transitions (DPT) and study the possible impact that a DPT could have in more realistic models of neutrino oscillations and their mean-field approximation.

The two leading hypotheses for the Galactic Center excess (GCE) in the Fermi data are an unresolved population of faint millisecond pulsars (MSPs) and dark-matter (DM) annihilation. The dichotomy between these explanations is typically reflected by modeling them as two separate emission components. However, point sources (PSs) such as MSPs become statistically degenerate with smooth Poisson emission in the ultrafaint limit (formally where each source is expected to contribute much less than one photon on average), leading to an ambiguity that can render questions such as whether the emission is PS-like or Poissonian in nature ill defined. We present a conceptually new approach that describes the PS and Poisson emission in a unified manner and only afterwards derives constraints on the Poissonian component from the so obtained results. For the implementation of this approach, we leverage deep learning techniques, centered around a neural network-based method for histogram regression that expresses uncertainties in terms of quantiles. We demonstrate that our method is robust against a number of systematics that have plagued previous approaches, in particular DM/PS misattribution. In the Fermi data, we find a faint GCE described by a median source-count distribution (SCD) peaked at a flux of $\sim 4\times {10}^{-11}\text{counts}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ (corresponding to $\sim 3–4$ expected counts per PS), which would require $N\sim \mathcal{O}({10}^4)$ sources to explain the entire excess (median value $N=29$,300 across the sky). Although faint, this SCD allows us to derive the constraint ${\eta }_P\le 66\%$ for the Poissonian fraction of the GCE flux ${\eta }_P$ at 95% confidence, suggesting that a substantial amount of the GCE flux is due to PSs.

We consider spherically symmetric accretion onto a small, possibly primordial, black hole residing at the center of a neutron star governed by a cold nuclear equation of state (EOS). We generalize the relativistic Bondi solution for such EOSs, approximated by piecewise polytropes, and thereby obtain analytical expressions for the steady-state matter profiles and accretion rates. We compare these rates with those found by time-dependent, general relativistic hydrodynamical simulations upon relaxation and find excellent agreement. We consider several different candidate EOSs, neutron star masses and central densities and find that the accretion rates vary only little, resulting in an accretion rate that depends primarily on the black hole mass, and only weakly on the properties of the neutron star.

Stimulated by the recent LHCb observation of a new exotic charged structure $T_{cc}^{+}$, we propose to use the central diffractive mechanism existing in the $\gamma p\to D^{+}{\overline{T}}_{cc}^{-}{\mathrm{\Lambda }}_c^{+}$ (${\overline{T}}_{cc}^{-}$ is the antiparticle of $T_{cc}^{+}$) reaction to produce $T_{cc}^{+}$. Our theoretical approach is based on the chiral unitary theory where the $T_{cc}^{+}$ resonance is dynamically generated. With the coupling constant of the $T_{cc}^{+}$ to $D{D}^{*}$ channel obtained from chiral unitary theory, the total cross sections of the $\gamma p\to D^{+}{\overline{T}}_{cc}^{-}{\mathrm{\Lambda }}_c^{+}$ reaction are evaluated. Our study indicates that the cross section for $\gamma p\to D^{+}{\overline{T}}_{cc}^{-}{\mathrm{\Lambda }}_c^{+}$ reaction is on the order of 1.0 pb, which is accessible at the proposed the Electron-Ion Collider in China [Front. Phys. (Beijing) 16, 64701 (2021)] or the U.S. [Eur. Phys. J. A 52, 268 (2016)] due to the higher luminosity. If measured and confirmed in the future experiments, the predicted total cross sections can be used to verify the (molecular) nature of the $T_{cc}^{+}$.

In addition to the existing strong indications for lepton flavor universality violation in low-energy precision experiments, the CMS Collaboration at CERN recently released an analysis of nonresonant dilepton pairs which could constitute the first sign of lepton flavor universality violation in high-energy searches at the LHC. In this article, we show that the Cabibbo-angle anomaly, an (apparent) violation of first row and column Cabibbo-Kobayashi-Maskawa (CKM) matrix unitarity with $\approx 3\sigma$ significance, and the CMS result can be correlated and commonly explained in a model-independent way by the operator $[Q_{\ell q}^{(3)}{]}_{1111}=({\overline{\ell }}_1{\gamma }^{\mu }{\sigma }^I{\ell }_1)({\overline{q}}_1{\gamma }_{\mu }{\sigma }^I{q}_1)$. This is possible without violating the bounds from the nonresonant dilepton search of ATLAS (which interestingly also observed slightly more events than expected in the electron channel) nor from $R(\pi )=\pi \to \mu \nu /\pi \to e\nu$. We find a combined preference for the new physics hypothesis of $4.5\sigma$ and predict $1.0004<R(\pi )<1.0009$ (95% C.L.) which can be tested in the near future with the forthcoming results of the PEN experiment.

We study flipped $SU(5)\times U(1)$ grand unified theories (GUTs) with ${\mathrm{\Gamma }}_3\simeq A_4$ modular symmetry. We propose two models with different modular weights assignments, where the fermion mass hierarchy can arise from weighton fields. In order to relax the constraint on the Dirac neutrino Yukawa matrix we appeal to mechanisms which allow incomplete GUT representations, allowing a good fit to quark and charged lepton masses and quark mixing for a single modulus field $\tau$, with the neutrino masses and lepton mixing well determined by the type-I seesaw mechanism, at the expense of some tuning. We also discuss the double seesaw possibility allowed by the extra singlets generically predicted in such string inspired theories.

We present here a novel and testable mechanism for leptogenesis, which is characterized by a purely thermal generation of lepton asymmetry via scalar decay. Guided by the thermal mass matrix diagonalization in the finite-temperature regime, we propose a scenario in which the baryon asymmetry is formulated in terms of the masses and mixing from hierarchical Dirac neutrinos, as well as a vacuum scale accountable for the sub-eV neutrino masses. This allows a natural and direct link between the high-scale $CP$ asymmetry and the low-energy Dirac $CP$-violating phase without involved model structures, and thus circumvents the haunting problem encountered in general leptogenesis scenarios. The mechanism can also be applied as a prototype for solving the baryon asymmetry problem to a broad class of well-motivated model buildings.

We present the generalized parton distributions (GPDs) for the valence quarks of the pion and the kaon in both momentum space and position space within the basis light-front quantization framework. These GPDs are obtained from the eigenvectors of a light-front effective Hamiltonian consisting of the holographic quantum chromodynamics (QCD) confinement potential, a complementary longitudinal confinement potential, and the color-singlet Nambu-Jona–Lasinio interactions for the valence quarks of mesons. We then calculate the generalized form factors of the pion and the kaon from the moments of these GPDs. Combining the tensor form factors with the electromagnetic form factors, we subsequently evaluate the impact parameter dependent probability density of transversely polarized quarks inside the pion and the kaon. The numerical results for the generalized form factors, corresponding charges, as well as those for the probability densities and the transverse shift of the polarized densities are consistent with lattice QCD simulations and with chiral quark models.

We develop an inverse matrix method to solve for resonance masses from a dispersion relation obeyed by a correlation function. Given the operator product expansion (OPE) of a correlation function in the deep Euclidean region, we obtain the nonperturbative spectral density, which exhibits resonance structures naturally. The value of the gluon condensate in the OPE is fixed by producing the $\rho$ meson mass in the formalism, and then input into the dispersion relations for the scalar, pseudoscalar, and tensor glueballs. It is shown that the low-energy limit of the correlation function for the scalar glueball, derived from the spectral density, discriminates the lattice estimate for the triple-gluon condensate from the single-instanton estimate. The spectral densities for the scalar and pseudoscalar glueballs reveal a double-peak structure; the peak located at lower mass implies that the $f_0(500)$ and $f_0(980)$ ($\eta$ ad ${\eta }^{\prime }$) mesons contain small amount of gluonium components, and should be included into scalar (pseudoscalar) mixing frameworks. Another peak determines the scalar (pseudoscalar) glueball mass around 1.50 (1.75) GeV with a broad width about 200 MeV, suggesting that the $f_0(1370)$, $f_0(1500)$, and $f_0(1710)$ [$\eta (1760)$] mesons are the glue-rich states. We also predict the topological susceptability ${\chi }_t^{1/4}=75\mathrm{MeV}–78\mathrm{MeV}$, deduced from the correlation function for the pseudoscalar glueball at zero momentum. Our analysis gives no resonance solution for the tensor glueball, which may be attributed to the insufficient nonperturbative condensate information in the currently available OPE.

The flagship measurement of the JUNO experiment is the determination of the neutrino mass ordering. Here we revisit its prospects to make this determination by 2030, using the current global knowledge of the relevant neutrino parameters as well as current information on the reactor configuration and the critical parameters of the JUNO detector. We pay particular attention to the nonlinear detector energy response. Using the measurement of ${\theta }_{13}$ from Daya Bay, but without information from other experiments, we estimate the probability of JUNO determining the neutrino mass ordering at $\ge 3\sigma$ to be 31% by 2030. As this probability is particularly sensitive to the true values of the oscillation parameters, especially $\mathrm{\Delta }{m}_{21}^2$, JUNO’s improved measurements of ${\sin }^2{\theta }_{12}$, $\mathrm{\Delta }{m}_{21}^2$ and $|\mathrm{\Delta }{m}_{ee}^2|$, obtained after a couple of years of operation, will allow an updated estimate of the probability that JUNO alone can determine the neutrino mass ordering by the end of the decade. Combining JUNO’s measurement of $|\mathrm{\Delta }{m}_{ee}^2|$ with other experiments in a global fit will most likely lead to an earlier determination of the mass ordering.

The largest tau neutrino dataset to date is IceCube’s atmospheric tau neutrino appearance dataset containing $>1000$ tau neutrino and antineutrino events as determined by a fit to a standard three-flavor oscillation framework. On an event-by-event basis, however, it is impossible to know that any given event is a tau neutrino as they are identical to either an electron neutrino charged-current event or a neutral-current interaction of any active flavor. Nonetheless, we conclusively show that, using only the cascade sample even without knowledge of the oscillation parameters and without assuming that the lepton mixing matrix is unitary, tau neutrino identification is still possible and there is no viable scenario in which all of the tau neutrino candidates are actually electron neutrinos. This is primarily due to the matter effect and the tau lepton production threshold, as well as the fact that tau neutrinos are systematically reconstructed at a lower energy than electron neutrinos due to one or more outgoing neutrinos. This conclusively shows that it is possible for an atmospheric neutrino oscillation experiment to confirm that $U_{\tau 1}$, $U_{\tau 2}$, and $U_{\tau 3}$ are not all zero even with limited particle identification.