We derive the second post-Newtonian solution for the quasi-Keplerian motion of a charged test particle in the Reissner-Nordström spacetime under harmonic coordinates. We formulate the solution in terms of the test particle’s orbital energy and angular momentum, both of which are constants at the second post-Newtonian order. The charge effects on the test particle’s motion including the orbital period and perihelion precession are displayed explicitly. Our results can be applied to the cases in which the test particle has small charge-to-mass ratio, or the test particle has arbitrary charge-to-mass ratio but the multiplication of the test particle and the gravitational source’s charge-to-mass ratios is much smaller than 1.

We study the combined effects of a finite volume and an external magnetic field on the charged two-pion correlation function. For these purposes, we consider a dilute system of pions where the finite volume effects are introduced computing the pion wave functions with rigid boundary conditions in a cylindrical geometry in the presence of a uniform and constant magnetic field. We find that for slow pions, namely, for the case where the average pair momentum is small, the correlation function shows a large distortion, as opposed to the case where the average pair momentum is large. For a finite density system, the intercept of the correlation function is reduced, signaling the increasing importance of the pion ground state contribution. An increasing strength of the magnetic field reduces the importance of the ground state and the intercept becomes closer to 2.

The effects of reflecting boundaries on vacuum electric field fluctuations are treated. The presence of the boundaries can enhance these fluctuations and possibly lead to observable effects. The electric field fluctuations lead to voltage fluctuations along the worldline of a charged particle moving perpendicularly to a pair of reflecting plates. These voltage fluctuations in turn lead to fluctuations in the kinetic energy of the particle, which may enhance the probability of quantum barrier penetration by the particle. A recent experiment by Moddel et al. is discussed as a possible example of this enhanced barrier penetration probability.

A number of stability criteria exist for dark energy theories, associated with requiring the absence of ghost, gradient and tachyonic instabilities. Tachyonic instabilities are the least well explored of these in the dark energy context and we here discuss and derive criteria for their presence and size in detail. Our findings suggest that, while the absence of ghost and gradient instabilities is indeed essential for physically viable models and so priors associated with the absence of such instabilities significantly increase the efficiency of parameter estimations without introducing unphysical biases, this is not the case for tachyonic instabilities. Even strong such instabilities can be present without spoiling the cosmological validity of the underlying models. Therefore, we caution against using exclusion priors based on requiring the absence of (strong) tachyonic instabilities in deriving cosmological parameter constraints. We illustrate this by explicitly computing such constraints within the context of Horndeski theories, while quantifying the size and effect of related tachyonic instabilities.

Recent gravitational wave observations allow us to probe gravity in the strong and dynamical field regime. In this paper, we focus on testing Einstein-dilation Gauss-Bonnet gravity which is motivated by string theory. In particular, we use two new neutron star black hole binaries (GW200105 and GW200115). We also consider GW190814 which is consistent with both a binary black hole and a neutron star black hole binary. Adopting the leading post-Newtonian correction and carrying out a Bayesian Markov-chain Monte Carlo analysis, we derive the 90% credible upper bound on the coupling constant of the theory as $\sqrt{{\alpha }_{\mathrm{GB}}}\lesssim 1.33\mathrm{km}$, whose consistency is checked with an independent Fisher analysis. This bound is stronger than the bound obtained in previous literature by combining selected binary black hole events in GWTC-1 and GWTC-2 catalogs. We also derive a combined bound of $\sqrt{{\alpha }_{\mathrm{GB}}}\lesssim 1.18\mathrm{km}$ by stacking GW200105, GW200115, GW190814, and selected binary black hole events. In order to check the validity of the effect of higher post-Newtonian terms, we derive corrections to the waveform phase up to second post-Newtonian order by mapping results in scalar-tensor theories to Einstein-dilation Gauss-Bonnet gravity. We find that such higher-order terms improve the bounds by 14.5% for GW200105 and 6.9% for GW200115, respectively.

We introduce a unified spin-weighted formalism to describe both timing and astrometric perturbations induced on astrophysical point sources by gravitational waves using a complex spin field on the sphere. This allows the use of spin-weighted spherical harmonics to analyze “astrochronometric” observables. This approach simplifies the interpretation and simulation of anisotropies induced in the observables by gravitational waves. It also allows a simplified derivation of angular cross-spectra of the observables and their relationship with generalized Hellings-Downs correlation functions. The spin-weighted formalism also allows an explicit connection between correlation components and the spin of gravitational wave polarizations and any presence of chirality. We also calculate expected signal-to-noise ratios for observables to compare the utility of timing and deflection observables.

The cosmic neutrino background (CNB) is a definite prediction of the standard cosmological model and its direct discovery would represent a milestone in cosmology and neutrino physics. In this work, we consider the capture of relic neutrinos on a tritium target as a possible way to detect the CNB, as aimed for by the PTOLEMY project. Crucial parameters for this measurement are the absolute neutrino mass $m_{\nu }$ and the local neutrino number density $n_{\nu }^{\mathrm{loc}}$. Within the $\mathrm{\Lambda }\mathrm{CDM}$ model, cosmology provides a stringent upper limit on the sum of neutrino masses of $\sum m_{\nu }<0.12\mathrm{eV}$, with further improvements expected soon from galaxy surveys by DESI and EUCLID. This makes the prospects for a CNB detection and a neutrino mass measurement in the laboratory very difficult. In this context, we consider a set of nonstandard cosmological models that allow for large neutrino masses ($m_{\nu }\sim 1\mathrm{eV}$), potentially in reach of the KATRIN neutrino mass experiment or upcoming neutrinoless double-beta decay searches. We show that the CNB detection prospects could be much higher in some of these models compared to those in $\mathrm{\Lambda }\mathrm{CDM}$, and discuss the potential for such a detection to discriminate between cosmological scenarios. Moreover, we provide a simple rule to estimate the required values of energy resolution, exposure, and background rate for a PTOLEMY-like experiment to cover a certain region in the $(m_{\nu },n_{\nu }^{\mathrm{loc}})$ parameter space. Alongside this paper, we publicly release a code to calculate the CNB sensitivity in a given cosmological model.

The images of ultrahigh-energy cosmic ray sources get distorted, in an energy dependent way, by the effects of Galactic and extragalactic magnetic fields. These deflections can also affect the observed cosmic ray spectrum, especially when the sources are transient. We study scenarios in which one or a few nearby extragalactic sources, such as Cen A or M81/M82, provide the dominant contribution to the cosmic ray flux above the ankle of the spectrum. We discuss the effects of the angular dispersion induced by the turbulent extragalactic magnetic fields, and the coherent deflections caused by the regular Galactic magnetic field, with the associated multiple imaging of the sources. We consider the possible contribution from those sources to the dipolar distribution discovered by the Pierre Auger Observatory above 8 EeV, as well as to the hot spots hinted in the observations by the Pierre Auger and Telescope Array observatories at higher energies, taking into account the mixed nature of the cosmic ray composition.

We discuss time reversal ($T$) violation in neutrino oscillations in generic new physics scenarios. A general parametrization is adopted to describe flavor evolution, which captures a wide range of new physics effects, including nonstandard neutrino interactions, nonunitarity, and sterile neutrinos in a model-independent way. In this framework, we discuss general properties of time reversal in the context of long-baseline neutrino experiments. Special attention is given to fundamental versus environmental $T$ violation in the presence of generic new physics. We point out that $T$ violation in the disappearance channel requires new physics, which modifies flavor mixing at neutrino production and detection. We use time-dependent perturbation theory to study the effect of nonconstant matter density along the neutrino path and quantify the effects for the well-studied baselines of the DUNE, T2HK, and T2HKK projects. The material presented here provides the phenomenological background for the model-independent test of $T$ violation proposed by us in [T. Schwetz and A. Segarra, Model-Independent Test of $T$ Violation in Neutrino Oscillations, Phys. Rev. Lett. 128, 091801 (2022).].

Thimble regularization of lattice field theories has been proposed as a solution to the infamous sign problem. It is conceptually very clean and powerful, but it is in practice limited by a potentially very serious issue: in general many thimbles can contribute to the computation of the functional integrals. Semiclassical arguments would suggest that the fundamental thimble could be sufficient to get the correct answer, but this hypothesis has been proven not to hold true in general. A first example of this failure has been put forward in the context of the Thirring model: the dominant thimble approximation is valid only in given regions of the parameter space of the theory. Since then a complete solution of this (simple) model in thimble regularization has been missing. In this paper we show that a full solution (taking the continuum limit) is indeed possible. It is possible thanks to a method we recently proposed which de facto evades the need to simulate on many thimbles.

We analyze quark-mass and $1/N_c$ corrections to all of the radiative transitions between the vector-meson nonet and the pseudoscalar-meson nonet within a chiral effective Lagrangian approach. We perform fits of the available coupling constants to experimental data and discuss the corresponding approximations. In terms of five (six) coupling constants, we obtain a reasonably good description of the twelve experimental decay rates.

Neutrino telescopes provide strong sensitivity to sterile-neutrino oscillations through matter effects occurring in the few TeV energy range for ${\mathrm{eV}}^2$-scale neutrino mass-squared splittings. Prior searches have focused on ${\nu }_{\mu }$ disappearance, which has a particularly strong sensitivity to the mixing angle ${\theta }_{24}$ via ${\nu }_{\mu }\to {\nu }_s$ transitions. Nowadays, the ${\nu }_{\mu }\to {\nu }_e$ and ${\nu }_{\mu }\to {\nu }_{\tau }$ appearance channels have been considered less promising at neutrino telescopes, due in part to the much smaller target volume for cascades relative to tracks. This work explores the detectability of these signatures at neutrino telescopes given present constraints on sterile-neutrino mixing, and as an example, forecasts the sensitivity of the IceCube Neutrino Observatory to the mixing angles ${\theta }_{14}$, ${\theta }_{24}$, and ${\theta }_{34}$ in the $3+1$ sterile-neutrino model using the cascade channel with 10 yr of data. We find that ${\nu }_{\tau }$ appearance signatures consistent with the existing IceCube ${\nu }_{\mu }$ disappearance best-fit point are discoverable for values of ${\theta }_{34}$ consistent with world constraints, and that the sterile-neutrino parameters favored by the BEST and gallium anomalies are expected to be testable at the 95% confidence level.

We consider how scalar fields affect the thermodynamic behavior of charged anti-de Sitter (AdS) black holes. We specifically investigate a class of ($3+1$)-dimensional exact hairy charged AdS black hole solutions to Einstein-Maxwell-scalar gravity, whose stable ground state and finite horizon area in the zero temperature limit make it of particular interest. We find that the reverse isoperimetric inequality is satisfied for this class and that there exists an intermediate range of the charge that admits reentrant phase behavior, the first example of this type of phase behavior in ($3+1$) dimensions in a consistent theory.

We study the thermal state of a two-dimensional conformal field theory, which is dual to the static BTZ black hole in the high temperature limit. After partitioning the boundary of the static BTZ slice into $N$ subsystems, we show that there is an underlying $C_{N-1}$ cluster algebra encoding entanglement patterns of the thermal state. We also demonstrate that the polytope encapsulating such patterns in a geometric manner for a fixed $N$ is the cyclohedron ${\mathcal{C}}_{N-1}$. Alternatively these patterns of entanglement can be represented in the space of geodesics (kinematic space) in terms of a Zamolodchikov $Y$ system of $C_{N-1}$ type. The boundary condition for such an $Y$ system is featuring the entropy of the BTZ black hole.

Using the superfield formalism and the master action approach, we prove, at both the classical and quantum levels, the dual equivalence between four-dimensional supersymmetric self-dual and topologically massive models coupled to dynamical matter.

Bubble universes and traversable wormholes in general relativity can be realized as two sides of the same concept. To exemplify it, we find, display, and study in a unified manner a Minkowski-Minkowski closed universe and a Minkowski-Minkowski traversable wormhole. By joining two 3-dimensional flat balls along a thin shell two-sphere of matter, i.e., a spherical domain wall, into a single spacetime one gets a Minkowski-Minkowski static closed universe, i.e., a bubble universe. By joining two 3-dimensional complements of flat balls along a thin shell two-sphere of matter, i.e., a spherical throat, into a single spacetime one gets a Minkowski-Minkowski static open universe which is a traversable wormhole. Thus, Minkowski-Minkowski bubble universes and wormholes can be seen as complementary to each other. It is also striking that these two spacetimes, the Minkowski-Minkowski bubble universe and the Minkowski-Minkowski traversable wormhole, have resemblances with two well-known static universes of general relativity. The Minkowski-Minkowski static closed universe, i.e., the Minkowski-Minkowski bubble universe, resembles in many aspects the Einstein universe, i.e., a static closed spherical universe homogeneously filled with dust matter and with a cosmological constant. The Minkowski-Minkowski static open universe, i.e., the Minkowski-Minkowski traversable wormhole, resembles the Friedmann static universe, i.e., a static open hyperbolic universe homogeneously filled with negative energy density dust and with a negative cosmological, which is a universe with two disjoint branes, or branches, and can be considered a failed wormhole. In this light, the Einstein static closed universe and the Friedmann static open universe should also be seen as the two sides of the same concept, i.e., they are complementary to each other. The scheme is completed by performing a linear stability analysis for the Minkowski-Minkowski bubble universe and the Minkowski-Minkowski traversable wormhole and also by comparing it to the stability of the Einstein static universe and the Friedmann static universe, respectively. This complementarity between bubble universes and traversable wormholes, that exists for these instances of static spacetimes, can be carried out for dynamical spacetimes, indicating that such a complementarity is quite general. The overall study suggests that bubble universes and traversable wormholes can be seen as coming out of the same concept, and thus, if one type of solution exists the other should also exist.

We expose the phenomenology of the massless dilaton theory in the Solar system for a nonuniversal quadratic coupling between the scalar field which represents the dilaton and the matter. Modified post-Newtonian equations of motion of an $N$-body system and the light time travel are derived from the action of the theory. We use the physical properties of the main planets of the Solar system to reduce the number of parameters to be tested to three in the linear coupling case. In the linear case, we have a universal coupling constant ${\alpha }_0$ and two coupling constants ${\alpha }_T$ and ${\alpha }_G$ related, respectively, to the telluric bodies and to the gaseous bodies. We then use the planetary ephemeris, INPOP19a, in order to constrain these constants. We succeeded to constrain the linear coupling scenario, and the constraints read ${\alpha }_0=(1.01\pm 23.7)\times {10}^{-5}$, ${\alpha }_T=(0.00\pm 24.5)\times {10}^{-6}$, ${\alpha }_G=(-1.46\pm 12.0)\times {10}^{-5}$, at the 99.5% C.L.

We study a Lagrangian with a cubic Galileon term and a standard scalar-field kinetic contribution with two exponential potentials. In this model the Galileon field generates scaling solutions in which the density of the scalar field $\varphi$ scales in the same manner as the matter density at early-time. These solutions are of high interest because the scalar field can then be compatible with the energy scale of particle physics and can alleviate the coincidence problem. The phenomenology of linear perturbations is thoroughly discussed, including all the relevant effects on the observables. Additionally, we use cosmic microwave background temperature-temperature and lensing power spectra by Planck 2018, the baryon acoustic oscillations measurements from the 6dF galaxy survey and SDSS and supernovae type Ia data from Pantheon in order to place constraints on the parameters of the model. We find that despite its interesting phenomenology, the model we investigate does not produce a better fit to data with respect to $\mathrm{\Lambda }\mathrm{CDM}$, and it does not seem to be able to ease the tension between high and low redshift data.

We study the halo mass function (HMF) in modified gravity (MG) models using a set of large $N$-body simulations—the elephant suite. We consider two popular beyond-general-relativity scenarios: the Hu-Sawicki chameleon $f(R)$ model and the normal branch of the Dvali-Gabadadze-Porrati (nDGP) braneworld. We show that in MG, analytic formulation based on the Press-Schechter framework offers a grossly inaccurate description of the HMF. We find, however, that once the HMF is expressed in terms of the dimensionless multiplicity function it approximately assumes a redshift-independent universal character for all the models. Exploiting this property, we propose universal fits for the MG HMF in terms of their fractional departures from the $\mathrm{\Lambda }\mathrm{CDM}$ case. We find two enclosed formulas, one for $f(R)$ and another for nDGP, that provide a reliable description of the HMF over the mass range covered by the simulations. These are accurate to a few percent with respect to the $N$-body data. We test the extrapolation potential of our fits against separate simulations with a different cosmological background and mass resolution and find very good accuracy, within $\sim 10\%$. A particularly interesting finding from our analysis is a Gaussian-like shape of the HMF deviation that seems to appear universally across the whole $f(R)$ family, peaking at a mass variance scale characteristic for each $f(R)$ variant. We attribute this behavior to the specific physics of the environmentally dependent chameleon screening models.