Gravitational waves from extreme gravity events such as the coalescence of two black holes in a binary system fill our observable Universe, bearing with them the underlying theory of gravity driving their process. One compelling alternative theory of gravity—known as Einstein-dilaton Gauss-Bonnet gravity motivated by string theory—describes the presence of an additional dilaton scalar field coupled directly to higher orders of the curvature, effectively describing a “fifth force” interaction and the emission of scalar dipole radiation between two scalarized black holes. Most previous studies focused on considering only the leading correction to the inspiral portion of the binary black hole waveforms. In our recent paper, we carried out inspiral-merger-ringdown consistency tests in this string-inspired gravity by including corrections to both the inspiral and ringdown portions, as well as those to the mass and spin of remnant black holes, valid to quadratic order in spin. We here extend the analysis by directly computing bounds on the theoretical coupling constant using the full inspiral-merger-ringdown waveform rather than treating the inspiral and merger-ringdown portions separately. We also consider the corrections valid to quartic order in spin to justify the validity of black hole’s slow-rotation approximation. We find the quasinormal mode corrections to the waveform to be particularly important for high-mass events such as GW170729, in which the dilaton fields’ small-coupling approximation fails without such effects included. We also show that future space-based and multiband gravitational-wave observations have the potential to go beyond existing bounds on the theory. The bounds presented here are comparable to those found via the inspiral-merger-ringdown consistency tests.

In this paper, we have continued the work of Herrera et al. [1] in $f(G)$ gravitational theory. For this purpose, a spherically symmetric fluid exhibiting locally anisotropic pressure along with the energy density, is taken under consideration. The perturbation scheme is imposed on modified field equations and the dynamical equations. The collapse equation is derived from these perturbed equations which assists to disclose the instability zone under both Newtonian and post-Newtonian constraints. It is wrapped up by concluding that dynamical instability is interpreted by the adiabatic index $\mathrm{\Gamma }$ which relies on the anisotropic pressure, energy density, and the dark source terms due to $f(G)$ gravity.

A compact binary system implicating at least one rotating neutron star undergoes a sequence of four gravitomagnetic tidal resonances as it inspirals toward its final merger. These resonances have a dynamical impact on the binary’s orbital motion, and thus on the phasing of the emitted gravitational waves. The resonances are produced by the inertial modes of vibration of the rotating star, and they occur when the orbital frequency becomes momentarily equal to a mode eigenfrequency. Four distinct modes are involved, and their eigenfrequencies are equal, up to a numerical factor of order unity, to the star’s rotational angular velocity. The resonances occur within the frequency band of interferometric gravitational-wave detectors when the star spins at a frequency that lies within this band; the phenomenon is therefore of relevance to LIGO/Virgo for rotation rates comparable to 100 Hz. The resonances are driven by the gravitomagnetic tidal field created by the companion star; this is described by a post-Newtonian vector potential (the time-space components of the metric tensor), which is produced by the mass currents associated with the orbital motion. The gravitomagnetic tidal resonances were identified previously by Flanagan and Racine [Phys. Rev. D 75, 044001 (2007)], but these authors accounted only for the response of a single mode, the $r$-mode, a special case of inertial modes. All four relevant inertial modes (including the $r$-mode) are included in the analysis presented in this paper. The total accumulated gravitational-wave phase shift caused by the gravitomagnetic tidal resonances is shown to range from approximately ${10}^{-2}$ radians when the spin and orbital angular momenta are aligned to approximately ${10}^{-1}$ radians when the angular momenta are antialigned. Such phase shifts are small, but they will become measurable in the coming decades with the deployment of the next generation of gravitational-wave detectors (Cosmic Explorer, Einstein Telescope); they might even come to light within this decade, thanks to planned improvements in the current detectors (LIGO $\mathrm{A}+$). With good constraints on the binary masses and spins gathered from the inspiral waveform, the phase shifts incurred during the gravitomagnetic tidal resonances deliver information regarding the internal structure of the rotating neutron star, and therefore on the equation of state of nuclear matter at high densities.

TEOBResumS and SEOBNRv4 are the two existing semianalytical gravitational waveform models for spin-aligned coalescing black hole binaries based on the effective-one-body (EOB) approach. They are informed by numerical relativity simulations and provide the relative dynamics and waveforms from early inspiral to plunge, merger, and ringdown. The central building block of each model is the EOB resummed Hamiltonian. The two models implement different Hamiltonians that are both deformations of the Hamiltonian of a test spinning black hole moving around a Kerr black hole. Here we analytically compare, element by element, the two Hamiltonians. In particular: we illustrate that one can introduce a centrifugal radius in SEOBNRv4, so to rewrite the Hamiltonian in a more compact form that is analogous to the one of TEOBResumS. The latter centrifugal radius cannot, however, be identified with the one used in TEOBResumS because the two models differ in their ways of incorporating spin effects in their respective deformations of the background Kerr Hamiltonian. We performed extensive comparisons between the energetics corresponding to the two Hamiltonians using gauge-invariant quantities. Finally, as an exploratory investigation, we apply the postadiabatic approximation to the newly rewritten SEOBNRv4 Hamiltonian, illustrating that it is possible to generate long-inspiral waveforms with negligible computational cost.

In this work we investigate the weak deflection angle of light from an exact black hole within nonlinear electrodynamics. First, we calculate the Gaussian optical curvature using the optical spacetime geometry. With the help of modern geometrical methods popularized by Gibbons and Werner, we examine the deflection angle of light from an exact black hole. To do this, we determine the optical Gaussian curvature and apply the Gauss-Bonnet theorem to the optical metric and calculate the leading terms of the deflection angle in the weak-limit approximation. Furthermore, we also study the plasma medium’s effect on weak gravitational lensing by an exact black hole. Hence, we determine the effect of nonlinear electrodynamics on the deflection angle in a weak gravitational field.

With the recent dawn of the multimessenger astronomy era a new window has opened to explore the constituents of matter and their interactions under extreme conditions. One of the pending challenges of modern physics is to probe the microscopic equation of state (EoS) of cold and dense matter via macroscopic neutron star observations such as their masses and radii. Still unanswered issues concern the detailed composition of matter in the core of neutron stars at high pressure and the possible presence of, e.g., hyperons or quarks. By means of a nonperturbative functional renormalization group approach the influence of quantum and density fluctuations on the quark matter EoS in $\beta$-equilibrium is investigated within two- and three-flavor quark-meson model truncations and compared to results obtained with common mean-field approximations where important fluctuations are usually ignored. We find that they strongly impact the quark matter EoS.

We formulate hydrodynamic equations for nonsuperfluid multicomponent magnetized charged relativistic mixtures, taking into account chemical reactions as well as viscosity, diffusion, thermodiffusion, and thermal conductivity effects. The resulting equations have a rather simple form and can be readily applied, e.g., for studying magnetothermal evolution of neutron stars. We also establish a link between our formalism and the results known in the literature and express the phenomenological diffusion coefficients through momentum transfer rates which are calculated from microscopic theory.

Collisions of twisted particles—that is, non-plane-wave states of photons, electrons, or any other particle, equipped with a nonzero orbital angular momentum (OAM) with respect to its propagation direction—offer novel ways to probe particle structure and interactions. Recently, we argued that resonance production in twisted photon collisions or twisted $e^{+}{e}^{-}$ annihilation gives access to parity- and spin-sensitive observables in inclusive cross sections, even when the initial particles are unpolarized. Here, we explore these features in detail, providing a qualitative picture and illustrating it with numerical examples. We show how one can detect parity-violating effects in collisions of unpolarized twisted photons and how one can produce almost 100% polarized vector mesons in unpolarized twisted $e^{+}{e}^{-}$ annihilation. These examples highlight the unprecedented level of control over polarization offered by twisted particles, impossible in the usual plane wave collisions.

Electron-positron pair production for inhomogeneous electric and magnetic fields oscillating in space and time is investigated. By employing accurate numerical methods (Furry-picture quantization and quantum kinetic theory), final particle momentum spectra are calculated and analyzed in terms of effective models. Furthermore, criteria for the applicability of approximate methods are derived and discussed. In this context, special focus is placed on the local density approximation, where fields are assumed to be locally homogeneous in space. Eventually, we apply our findings to the multiphoton regime. Special emphasis is on the importance of linear momentum conservation and the effect of its absence in momentum spectra within approximations based on local homogeneity of the fields.

We establish a simple formula for the minimal dimension of operators leading to any helicity amplitude. It eases the systematic enumeration of independent operators from the construction of massless nonfactorizable on-shell amplitudes. Little-group constraints can then be solved algorithmically for each helicity configuration to extract a complete set of spinor structures with lowest dimension. Occasionally, further reduction using momentum conservation, on-shell conditions and Schouten identities is required. A systematic procedure to account for the latter is presented. Dressing spinor structures with dot products of momenta finally yields the independent Lorentz structures for each helicity amplitude. We apply these procedures to amplitudes involving particles of spins $0,1/2,1,2$. Spin statistics and elementary selection rules due to gauge symmetry lead to an enumeration of operators involving gravitons and standard-model particles, in the effective field theory denoted GRSMEFT. We also list the independent spinor structures generated by operators involving standard-model particles only. In both cases, we cover operators of dimension up to eight.

Many existing or proposed intensity-frontier search experiments look for decay signatures of light long-lived particles (LLPs), highly displaced from the interaction point, in a distant detector that is well-shielded from the Standard Model background. This approach is, however, limited to new particles with decay lengths similar to or larger than the baseline of those experiments. In this study, we discuss how this basic constraint can be overcome in non-minimal beyond standard model scenarios. If more than one light new particle is present in the model, an additional secondary production of LLPs may take place right in front of the detector, opening this way a new lifetime regime to be probed. We illustrate the prospects of such searches in the future experiments FASER, MATHUSLA, and SHiP, for representative models, emphasizing possible connections to dark matter or an anomalous magnetic moment of muon. We also analyze additional advantages from employing dedicated neutrino detectors placed in front of the main decay volume.

Many-body quantum systems far from equilibrium can exhibit universal scaling dynamics which defy standard classification schemes. Here, we disentangle the dominant excitations in the universal dynamics of highly occupied $N$-component scalar systems using unequal-time correlators. While previous equal-time studies have conjectured the infrared properties to be universal for all $N$, we clearly identify for the first time two fundamentally different phenomena relevant at different $N$. We find all $N\ge 3$ to be indeed dominated by the same Lorentzian “large-$N$” peak, whereas $N=1$ is characterized instead by a non-Lorentzian peak with different properties, and for $N=2$, we see a mixture of two contributions. Our results represent a crucial step toward obtaining a classification scheme of universality classes far from equilibrium.

We classify discrete modular symmetries in the effective action of Type IIB string on toroidal orientifolds with three-form fluxes, emphasizing on $T^6/{\mathbb{Z}}_2$ and $T^6/({\mathbb{Z}}_2\times {\mathbb{Z}}_2^{\prime })$ orientifold backgrounds. In the three-form flux background, the modular group is spontaneously broken down to its congruence subgroup whose pattern is severely constrained by a quantization of fluxes and tadpole cancellation conditions. We explicitly demonstrate that the congruence subgroups appearing in the effective action arise on magnetized D-branes wrapping certain cycles of tori.

The Feynman propagator in curved spacetime admits an asymptotic (Schwinger-DeWitt) series expansion in derivatives of the metric. Remarkably, all terms in the series containing the Ricci scalar $R$ can be summed exactly. We show that this (nonperturbative) property of the Schwinger-DeWitt series has a natural and equivalent counterpart in the adiabatic (Parker-Fulling) series expansion of the scalar modes in an homogeneous cosmological spacetime. The equivalence between both $R$-summed adiabatic expansions can be further extended when a background scalar field is also present.

Intersection numbers of Stokes polytopes living in complex projective space are computed using the techniques employed to find the inverse string Kawai-Lewellen-Tye (KLT) matrix elements in terms of intersection numbers of associahedra. To do this requires an appropriate convex realization of Stokes polytopes in ${\mathbb{CP}}^n$ loaded with suitable generalizations of the Koba-Nielsen factor. The procedure is carried out explicitly for the lower point cases, and the prescription for the generic higher point cases is laid out as well. The intersection numbers are identified as scattering amplitudes corresponding to a theory the coupling constants of which are determined entirely in terms of the combinatorial weights of the Stokes polytopes. A parameter ${\alpha }^{\prime }$ having units of length is used to define the intersection numbers in a manner that yields the amplitudes of ${\varphi }^4$ theory to leading order when the limit of vanishing ${\alpha }^{\prime }$ limit is taken. Most importantly, we contrast and compare this method of understanding quartic vertices with previous string-theoretic attempts to obtain quartic interaction amplitudes.

Given that any communication is communication through quantum fields, we study here the scenario where a sender, Alice, causes information-carrying disturbances in a quantum field. We track the exact spread of these disturbances in space and time by using the technique of quantum information capsules (QIC). We find that the channel capacity between Alice and a receiver, Bob, is enhanced by Bob placing detectors not only inside but in addition also outside the causal future of Alice’s encoding operation. Intuitively, this type of superadditivity arises because the field outside the causal future of Alice is entangled with the field inside Alice’s causal future. Hence, the quantum noise picked up by Bob’s detectors outside Alice’s causal future is correlated with the noise of Bob’s detectors inside Alice’s causal future. In effect, this correlation allows Bob to improve the signal-to-noise ratio of those of his detectors which are in the causal future of Alice. Further, we develop the multimode generalization of the QIC technique. This allows us to extend the analysis to the case where Alice operates multiple localized and optionally entangled emitters. We apply the new techniques to the case where Alice enhances the channel capacity by operating multiple emitters that are suitably lined up and pretimed to generate a quantum shockwave in the field.

In this paper, we develop studies of the dynamical symmetry breaking in the Horava-Lifshitz four-fermion model for the specific case $z=3$ and explicitly demonstrate that for various space-time dimensions, one could arrive at the theory displaying both dynamical generation of the Lorentz symmetry for the kinetic term and arising the positively defined potential at the same time. At the same time, for $D=3$, the Lorentz-invariant Chern-Simons term is generated.

It has recently been demonstrated that static spatially regular scalar fields, which are nonminimally coupled to the electromagnetic field of a charged central black hole, can be supported in the exterior regions of the black-hole spacetime. In the present paper, we use analytical techniques in order to study the physical and mathematical properties of the externally supported linearized scalar field configurations (scalar “clouds”) in the dimensionless large-mass regime $\mu r_{+}\gg 1$ (here, $\mu$ and $r_{+}$ are respectively the proper mass of the supported scalar field and the outer horizon radius of the central supporting black hole). In particular, we derive a remarkably compact analytical formula for the discrete resonant spectrum $\{{\alpha }_n(\mu ;Q/M){\}}_{n=0}^{n=\infty }$ which characterizes the dimensionless coupling parameter of the composed black hole–nonminimally coupled linearized massive scalar field configurations. The physical significance of this resonant spectrum stems from the fact that, for a given value of the dimensionless black-hole electric charge $Q/M$, the fundamental (smallest) eigenvalue ${\alpha }_0(\mu )$ determines the critical existence line of the composed black hole–massive field system, a boundary line which separates nonlinearly coupled hairy charged black hole–massive scalar field configurations from bald Reissner-Nordström black holes. The analytical results derived in this paper are confirmed by direct numerical computations.