There exists a correspondence between black holes in nonlinear electrodynamics (NLED) and gravitational collapse of homogeneous dust with semiclassical corrections in the strong curvature regime that to our knowledge has not been noticed until now. We discuss the nature of such correspondence and explore what insights may be gained from considering black holes in NLED in the context of semiclassical dust collapse and vice versa.

The generalized uncertainty principle (GUP) is a phenomenological model whose purpose is to account for a minimal length scale (e.g., Planck scale or characteristic inverse-mass scale in effective quantum description) in quantum systems. In this paper, we study possible observational effects of GUP systems in their decoherence domain. We first derive coherent states associated to GUP and unveil that in the momentum representation they coincide with Tsallis probability amplitudes, whose nonextensivity parameter $q$ monotonically increases with the GUP deformation parameter $\beta$. Second, for $\beta <0$ (i.e., $q<1$), we show that, due to Bekner-Babenko inequality, the GUP is fully equivalent to information-theoretic uncertainty relations based on Tsallis-entropy-power. Finally, we invoke the maximal entropy principle known from estimation theory to reveal connection between the quasiclassical (decoherence) limit of GUP-related quantum theory and nonextensive thermostatistics of Tsallis. This might provide an exciting paradigm in a range of fields from quantum theory to analog gravity. For instance, in some quantum gravity theories, such as conformal gravity, aforementioned quasiclassical regime has relevant observational consequences. We discuss some of the implications.

In a quantum gravity theory, it is expected that the classical notion of spacetime disappears, leading to a quantum structure with new properties. A possible way to take into account these quantum effects is through a noncommutativity of spacetime coordinates. In the literature, there is not a clear way to describe at the same time a noncommutativity of spacetime and the phase-space noncommutativity of quantum mechanics. In this paper we address this issue by constructing a Drinfel’d twist in phase space which deals with both quantizations. This method can be applied to a noncommutativity which involves only space, leaving time aside. We apply our construction to the so-called $\lambda$-Minkowski and ${\mathbb{R}}_{\lambda }^3$ noncommutative spaces.

Holographic tensor networks associated to tilings of ($1+1$)-dimensional de Sitter spacetime are introduced. Basic features of these networks are discussed, compared, and contrasted with conjectured properties of quantum gravity in de Sitter spacetime. Notably, we highlight a correspondence between the quantum information capacity of the network and the cosmological constant.

A new description of free massless superfields of arbitrary superspin $\mathsf{Y}$ ($\mathsf{Y}>1/2$) is proposed. Following the first-order philosophy, we relax some of the properties (reality, gauge redundancy) of the unconstrained higher spin prepotentials and we construct first and half order invariants quantities. These are used to write trivially invariant actions. Additional auxiliary superfields that play the role of spin connections are used to enforce a new local symmetry that restores the degrees of freedom.

In recent work, we examined how different modes in the ringdown phase of a binary coalescence are excited as a function of the final plunge geometry. At least in the large mass ratio limit, we found a clean mapping between angles describing the plunge and the amplitude of different quasinormal modes (QNMs) which constitute the ringdown. In this study, we use that mapping to construct a waveform model expressed as a sum of QNMs where the mode amplitudes and phases are determined by the source plunge parameters. We first generate a large number of calibration waveforms and interpolate between fits of each mode amplitude and phase up to $\ell \le 8$ and $\ell -|m|\le 4$. The density of our calibration data allows us to resolve important features such as phase transition discontinuities at large misalignments. Using our ringdown waveform model, we then perform Bayesian parameter estimation with added white Gaussian noise to demonstrate that, in principle, the mode amplitudes can be measured and used to constrain the plunge geometry. We find that inferences are substantially improved by incorporating prior information constraining mode excitation, which motivates work to understand and characterize how the QNM excitation depends on the coalescence geometry. These results are part of a broader effort to map the mode excitation from arbitrary masses and spins, which will be useful for characterizing ringdown waves in upcoming gravitational-wave measurements.

We consider the periapsis shifts in dark matter distribution with a dense core. We model the dark matter distribution as an isotropic gas sphere, the Emden polytropic sphere of index 5 in general relativity. This model has a parameter range where all the energy conditions are satisfied in the entire region. Within the parameter range, the asymptotic analysis for stellar motion allows us to identify two competing effects on the bounded motion: the general-relativistic effect and a local-density effect of matter. Furthermore, using nearly circular bound orbits, we demonstrate that retrograde periapsis shifts occur near the center, where the local-density effect dominates over the general-relativistic effect, whereas prograde periapsis shifts occur in the far region, where the general-relativistic effect dominates over the local-density effect. This result means that a natural explanation for the retrograde periapsis shifts is not the existence of exotic objects (e.g., naked singularities or wormholes) but the local distribution of physically reasonable matter on the stellar orbit. Furthermore, it also implies that the periapsis shift plays a crucial role in distinguishing black hole alternatives, such as dark matter cores, from a pure black hole.

We consider a generic scattering process that takes place in a region of size $R$ inside the static patch of the de Sitter spacetime such that $R$ is smaller than the curvature length scale of the background. The effect of curvature can thus be studied perturbatively. We obtain the asymptotic electromagnetic field generated by the scattering process including the leading order correction due to the presence of de Sitter background and discuss its universal aspects. We finally calculate the resultant first order corrections to the flat spacetime velocity memory effect.

We introduce the Brans–Dick–de Rham–Gabadadze–Tolley massive gravity theory which is the new extension of nonlinear massive gravity. We demonstrate a detailed study of the cosmological properties of this theory of gravity, and we show the transformation of the Jordan frame to the Einstein frame. We obtain the cosmological background equations and show the analyses of self-accelerating solutions for explaining the accelerated expansion of the Universe. In the following, we analyze the background perturbations, which consist of tensor, vector, and scalar perturbations within the framework of the new extension of the de Rham–Gabadadze–Tolley massive gravity in the Friedman-Lemaître-Robertson-Walker cosmology.

Pulsar timing provides a sensitive probe of small-scale structure. Gravitational perturbations arising from an inhomogeneous environment could manifest as detectable perturbations in the pulsation phase. Consequently, pulsar timing arrays have been proposed as a probe of dark matter substructure on mass scales as small as ${10}^{-11}{M}_{\odot }$. Since the small-scale mass distribution is connected to early-Universe physics, pulsar timing can therefore constrain the thermal history prior to big bang nucleosynthesis (BBN), a period that remains largely unprobed. We explore here the prospects for pulsar timing arrays to detect the dark substructure imprinted by a period of early matter domination (EMD) prior to BBN. EMD amplifies density variations, leading to a population of highly dense sub-Earth-mass dark matter microhalos. We use recently developed semianalytic models to characterize the distribution of EMD-induced microhalos, and we evaluate the extent to which the pulsar timing distortions caused by these microhalos can be detected. Broadly, we find that sub-$0.1\text{−}\mu \mathrm{s}$ timing noise residuals are necessary to probe EMD. However, with 10-ns residuals, a pulsar timing array with just 70 pulsars could detect the evidence of an EMD epoch with 20 years of observation time if the reheat temperature is of order 10 MeV. With 40 years of observation time, pulsar timing arrays could probe EMD reheat temperatures as high as 150 MeV.

We analyze the response and thermal behavior of an Unruh-DeWitt detector as it travels through cosmological spacetimes, with special reference to the question of how to define surface gravity and temperature in dynamical spacetimes. Working within the quantum field theory on curved spacetime approximation, we consider a detector as it travels along geodesic and accelerated Kodama trajectories in de Sitter and asymptotically de Sitter FLRW spacetimes. By modelling the temperature of the detector using the detailed-balance form of the Kubo-Martin-Schwinger (KMS) conditions as it thermalizes, we can better understand the thermal behavior of the detector as it interacts with the quantum field, and use this to compare competing definitions of surface gravity and temperature that persist in the literature. These include the approaches of Kodama [Prog. Theor. Phys. 63, 1217 (1980).], Ashtekar and Krishnan [Living Rev. Relativity 7, 10 (2004).], Fodor et al. [Phys. Rev. D 54, 3882 (1996).], and Nielsen [Classical Quantum Gravity 23, 4637 (2006).]. While these are most often examined within the context of a dynamical black hole, here we shift focus to surface gravity on the evolving cosmological horizon.

We propose an extra $U(1{)}_X$ model with an alternative charge assignment for right-handed neutrinos. The type-II seesaw mechanism by a triplet Higgs field is promising for neutrino mass generation because of the alternative charge assignment. The small vacuum expectation value (VEV) of an additional Higgs doublet naturally leads to a very small VEV of the triplet Higgs field, and as a result, the smallness of neutrino mass can be understood. With the minimal Higgs field for $U(1{)}_X$ with the charge 1, right-handed neutrinos are candidates for Dirac dark matter (DM) and dark radiation (DR). We have derived and imposed the LHC bound, the DR constraint, and the bound from DM direct searches in the wide range of parameter space. Among various $U(1{)}_X$ choices, the DM direct search bound is found to be weakest for $U(1{)}_R$ where the constraints from thermal DM and non-negligible DR can be compatible. Such a number of the effective neutrino species would be interesting from the viewpoint of the so-called Hubble tension.

Fermion-boson stars are mixtures of the ordinary nuclear matter of a neutron star and bosonic dark matter. We dynamically evolve fermion-boson stars for the first time using a realistic equation of state for nuclear matter. We use our dynamical solutions to make a detailed study of the evolution of weakly and strongly perturbed static solutions. As examples of our findings, we identify a region of parameter space where weakly perturbed unstable static solutions migrate to a stable configuration, and we determine the criteria under which strongly perturbed stable static solutions will always move to a stable configuration instead of collapsing to a black hole.

The internal composition of neutron stars is still an open issue in astrophysics. Their innermost regions are impervious to light propagation and gravitational waves mostly carry global aspects of stars, meaning that only indirect inferences of their interiors could be obtained. Here we assume a hypothetical future scenario in which an equation of state softening due to a phase transition is identified and estimate the observational accuracy to differentiate a sharp phase transition from a smoother one (which we take to be associated with a mixed phase/state due to the unknown value of the surface tension of dense matter) in a region of a hybrid star by means of some electromagnetic and gravitational wave observables. We show that different transition constructions lead to similar sequences of stellar configurations due to their shared thermodynamic properties. In the most optimistic case—a strong quark-hadron density jump phase transition—radius observations require fractional uncertainties smaller than 1%–2% to differentiate mixed states from sharp phase transitions. For tidal deformabilities, relative uncertainties should be smaller than 5%–10%. However, for masses around the onset of stable quark cores, relative tidal deformability differences associated with strong sharp phase transitions and mixed states connecting the two pure phases could be much larger (up to around 20%–30%). All the above suggests that 2.5- and third-generation gravitational wave detectors and near-term electromagnetic missions may be able to start assessing some particular aspects of phase transitions in neutron stars. In addition, it points to some limitations on the equation of state recovery using typical neutron star observables and the impact of systematic uncertainties on modelings of the equation of state of hybrid stars. Finally, we briefly discuss other observables that may also be relevant for the probe of mixed states in stars.

The LIGO Scientific, Virgo and KAGRA Collaborations recently released the third gravitational wave transient catalog or GWTC-3, significantly expanding the number of gravitational wave signals. To address the—still uncertain—formation channels of the source compact binaries, their population properties must be characterized. The computational cost of the Bayesian hierarchical methods employed thus far scales with the size of the event catalogs, and such methods have until recently assumed fixed functional forms for the source distribution. Here we propose a fast and flexible method to reconstruct the population of LIGO-Virgo merging black hole (BH) binaries without such assumptions. For sufficiently high event statistics and sufficiently low individual event measurement error (relative to the scale of population features) a kernel density estimator (KDE) reconstruction of the event distribution will be accurate. We improve the accuracy and flexibility of KDE for finite event statistics using an adaptive bandwidth KDE (awKDE). We apply awKDE to publicly released parameter estimates for 44 significant (69) BH binary mergers in GWTC-2 (GWTC-3), in combination with a fast polynomial fit of search sensitivity, to obtain a nonparametric estimate of the mass distribution, and compare to Bayesian hierarchical methods. We also demonstrate a robust peak detection algorithm based on awKDE and use it to calculate the significance of the apparent peak in the BH mass distribution around $35{\mathrm{M}}_{\odot }$. We find such a peak is very unlikely to have occurred if the true distribution is a featureless power-law (significance of $3.6\sigma$ for confident GWTC-2 BBH events, $3.0\sigma$ for confident GWTC-3 BBH events).

We present a theoretical study of $a_0(1710)$, the isovector partner of $f_0(1710)$, in the process $D_s^{+}\to {\pi }^{+}{K}_S^0{K}_S^0$. The weak interaction part proceeds through the charm quark decay process: $c(\overline{s})\to (s+\overline{d}+u)(\overline{s})$, while the hadronization part takes place in two mechanisms, differing in how the quarks from the weak decay combine into $\pi K^{*}$ with a quark-antiquark pair $q\overline{q}$ with the vacuum quantum numbers. In addition to the contribution from the tree diagram of the $K^{*+}\to {\pi }^{+}{K}_S^0$, we have also considered the $K^{*}{\overline{K}}^{*}$ final-state interactions within the chiral unitary approach to generate the intermediate state $a_0(1710)$, then it decays into the final states $K_S^0{K}_S^0$. We find that the recent experimental measurements on the $K_S^0{K}_S^0$ and ${\pi }^{+}{K}_S^0$ invariant mass distributions can be well reproduced, and the proposed mechanism can provide valuable information on the nature of scalar $f_0(1710)$ and its isovector partner $a_0(1710)$.

As the strength of the magnetic field ($B$) becomes weak, novel phenomena, similar to the Hall effect in condensed matter physics, emerges both in charge and heat transport in a thermal QCD medium with a finite quark chemical potential ($\mu$). So we have calculated the transport coefficients in a kinetic theory within a quasiparticle framework, wherein we compute the effective mass of quarks for the aforesaid medium in a weak magnetic field (B) limit ($|eB|\ll T^2$; $T$ is temperature) by the perturbative thermal QCD up to one loop, which depends on $T$ and $B$ differently to left-handed (L) and right-handed (R) chiral modes of quarks, lifting the prevalent degeneracy in L and R modes in strong magnetic field limit ($|eB|\gg T^2$). Another implication of weak $B$ is that the transport coefficients assume a tensorial structure: The diagonal elements represent the usual (electrical and thermal) conductivities (${\sigma }_{\text{Ohmic}}$ and ${\kappa }_0$ as the coefficients of charge and heat transport, respectively) and the off-diagonal elements denote their Hall counterparts (${\sigma }_{\text{Hall}}$ and ${\kappa }_1$, respectively). It is found in charge transport that the magnetic field acts on L and R modes of the Ohmic part of electrical conductivity in an opposite manner, viz. ${\sigma }_{\text{Ohmic}}$ for L mode decreases and for R mode, increases with $B$ whereas the Hall-part ${\sigma }_{\text{Hall}}$ for both L and R modes always increases with $B$. In heat transport too, the effect of the magnetic field on the usual thermal conductivity (${\kappa }_0$) and Hall-type coefficient (${\kappa }_1$) in both modes is identical to the above-mentioned effect of $B$ on charge transport coefficients. We have then derived some coefficients from the above transport coefficients, namely Knudsen number ($\mathrm{\Omega }$ is the ratio of the mean-free path to the length scale of the system) and Lorenz number in Wiedemann-Franz law. The effect of $B$ on $\mathrm{\Omega }$ either with ${\kappa }_0$ or with ${\kappa }_1$ for both modes is identical to the behavior of ${\kappa }_0$ and ${\kappa }_1$ with $B$. The value of $\mathrm{\Omega }$ is always less than unity for the entire temperature range, validating our calculations. Lorenz number (${\kappa }_0/{\sigma }_{\text{Ohmic}}T$) and Hall-Lorenz number (${\kappa }_1/{\sigma }_{\text{Hall}}T$) for L mode increases and for R mode decreases with magnetic field. It also does not remain constant with temperature hence violating the Wiedemann-Franz law.

A natural composite Higgs demands the presence of light resonances at the TeV scale that, in general, are in conflict with bounds from flavor and $CP$ violation. We propose a composite model with a Froggatt-Nielsen mechanism that offers new possibilities for the origin of flavor. We analyze the interplay of partial compositeness and the horizontal U(1) symmetry in achieving the quark masses and mixing angles. We study the contributions to $\mathrm{\Delta }F=2$ 4-fermion operators, as well as to $\mathrm{\Delta }F=1$ and neutron dipole operators. We find scenarios in which the contribution to left-right and right-handed operators involving the first and second generations can be suppressed; in particular, for a region of parameter space it is possible to simultaneously suppress the mixed-chirality contribution to $K^0-{\overline{K}}^0$ mixing by one power of the Cabibbo angle, ${\lambda }_C$, and the dipole moments by ${\lambda }_C^2$ compared with anarchic partial compositeness, possibly making the resonances accessible at LHC. 4-fermion operators of $B_s$-meson mixing and left-handed operators are not suppressed.

A major task in phenomenology today is constraining the parameter space of Standard Model effective field theory and constructing models of fundamental physics from which the Standard Model derives. To this effect, we report an exhaustive list of sum rules for 4-fermion operators of dimension 6, connecting low-energy Wilson coefficients to cross sections in the UV. Unlike their dimension-8 counterparts which are amenable to a positivity bound, the discussion here is more involved due to the weaker convergence and indefinite signs of the dispersion integrals. We illustrate this by providing examples with weakly coupled UV completions leading to opposite signs of the Wilson coefficients for both convergent and nonconvergent dispersion integrals. We further decompose dispersion integrals under weak isospin and color groups, which lead to a tighter relation between IR measurements and UV models. These sum rules can become an effective tool for constructing consistent UV completions for Standard Model effective field theory following the prospective measurement of these Wilson coefficients.

Quantum simulations of QCD require digitization of the infinite-dimensional gluon field. Schemes for doing this with the minimum amount of qubits are desirable. We present a practical digitization for $SU(3)$ gauge theories via its discrete subgroup $S(1080)$. Using a modified action that allows classical simulations down to $a\approx 0.08\mathrm{fm}$, the low-lying glueball spectrum is computed with percent-level precision at multiple lattice spacings and is shown to extrapolate to the continuum limit $SU(3)$ results. This suggests that this digitization scheme is sufficient for precision quantum simulations of QCD.