New physics beyond the Standard Model can give rise to stochastic gravitational-wave backgrounds, for example, through cosmic strings. In this way, gravitational-wave searches with pulsar-timing arrays as well as existing and future laser interferometers may provide information on particle physics beyond the Standard Model. Here, we take one additional step and link particle physics beyond the Standard Model to quantum gravity. We investigate whether particle physics models that may give rise to cosmic strings can be embedded into an asymptotically safe theory of quantum gravity and matter. We focus on models where cosmic strings arise from U(1)-symmetry breaking in an extended Yukawa-Abelian-Higgs sector that may be part of a dark sector. We find a negative answer for the simplest model that can give rise to cosmic strings and also find constraints on an extended model. We tentatively conclude that cosmic strings are difficult to accommodate in asymptotically safe models. This fits well with the latest 15-year dataset and search for new physics from the NANOGrav Collaboration, which disfavors a stable-cosmic-string interpretation. In that sense, the recent data provide an indirect, albeit at present rather tentative, hint about the quantum theory of gravity.

In the free ${\square }^k$ scalar conformal field theory, there exist conserved and partially conserved higher-spin currents. We study their anomalous dimensions associated with ${\varphi }^{2n}$ interaction in the $\epsilon$ expansion. We derive general formulas for the leading corrections from the conformal multiplet recombination, and verify their consistency with crossing symmetry using the Lorentzian inversion formula. The results are further extended to the $\mathrm{O}(N)$ models.

We study the late-time behaviors of pseudo-(Rényi) entropy of locally excited states in rational conformal field theories. To construct the transition matrix, we utilize two nonorthogonal locally excited states that are created by the application of different descendant operators to vacuum. We show that when two descendant operators are generated by a single Virasoro generator acting on the same primary operator, the late-time excess of pseudoentropy and pseudo-Rényi entropy corresponds to the logarithm of the quantum dimension of the associated primary operator, in agreement with the case of entanglement entropy. However, for linear combination operators generated by the generic summation of Virasoro generators, we obtain a distinct late-time excess formula for the pseudo-(Rényi) entropy compared to that for (Rényi) entanglement entropy. As the mixing of holomorphic and antiholomorphic generators enhances the entanglement, in this case, the pseudo-(Rényi) entropy can receive an additional contribution. The additional contribution can be expressed as the pseudo-(Rényi) entropy of an effective transition matrix in a finite-dimensional Hilbert space.

Gravitational-wave signals from binaries that contain spinning black holes in general include an asymmetry between the $+m$ and $-m$ multipoles that is not included in most signal models used in LIGO-Virgo-KAGRA analysis to date. This asymmetry manifests itself in out-of-plane recoil of the final black hole and its inclusion in signal models is necessary both to measure this recoil, but also to accurately measure the full spin information of each black hole. We present the first model of the antisymmetric contribution to the dominant coprecessing-frame signal multipole throughout inspiral, merger, and ringdown. We model the antisymmetric contribution in the frequency domain, and take advantage of the approximations that the antisymmetric amplitude can be modeled as a ratio of the (already modeled) symmetric amplitude, and analytic relationships between the symmetric and antisymmetric phases during the inspiral and ringdown. The model is tuned to single-spin numerical-relativity simulations up to mass-ratio 8 and spin magnitudes of 0.8, and has been implemented in a recent phenomenological model for use in the fourth LIGO-Virgo-KAGRA observing run. However, the procedure described here can be easily applied to other time- or frequency-domain models.

Explicitly covariant analytical expressions are derived that describe the boundaries of shadows cast by massive particles scattered by a gravitating object. This covers scenarios with particles having effectively variable mass, such as photons in plasma, geodesics in higher dimensions, and particles interacting with a scalar field. The derived formula takes advantage of recent advances in understanding the relationship between slice-reducible Killing tensors and massive particle surfaces that generalize photon surfaces. The formula allows us to obtain simple approximations of scaling as the particle energy changes. We illustrate this structure using Kerr–Newman-Unti-Tomburino and Einstein-Maxwell-Dilaton black holes for both massive particles and photons in plasma. The versatility of this framework extends beyond astrophysics and has potential applications in analog models of gravity and condensed matter physics.

A superradiant cloud of ultralight bosons near a rotating black hole provides a smoking gun for particle physics in the infrared. However, tidal perturbations from a nearby binary companion can destabilize the boson cloud and even terminate superradiance. In this work, we consider the backreaction of superradiance termination to the dynamics of general binary orbits parametrized by their semilatus rectum, eccentricity and inclination angle. Our analysis focuses on extreme mass ratio inspiral systems and employs the period-average approximation to derive evolution equations of these binary parameters in the Newtonian limit. We find that the binary evolution history can be significantly modulated by the backreaction towards large circular equatorial orbits with reduced termination rate. This process can generically happen even away from the resonance bands. Our work therefore serves as a first step towards probing ultralight bosons through the statistics of extreme mass ratio inspiral binary parameters in the future.

Whether astrophysical black holes (BHs) can have charge is a question to be addressed by observations. In the era of gravitational wave (GW) astronomy, one can constrain the charge of a merged BH remnant using the merger-ringdown signal of the GW data. Extending earlier studies, we analyze five GW events in GWTC-3, assuming Kerr-Newman BHs. Our results show no strong evidence for a charged BH, and give a limit on the charge-to-mass-ratio $Q<0.37$ at 90% credible level. Due to the charge-spin degeneracy in the waveform and the limited signal-to-noise ratios, it is challenging for LIGO/Virgo/KAGRA observations to provide better constraints. We further simulate data for the Einstein Telescope, where signal-to-noise ratios can be as large as $\sim 270$ in the ringdown signal. These simulated events allow us to consider the 220, 221, and 330 ringdown modes altogether, which can help break the charge-spin degeneracy. The analysis of a simulated GW150914-like signal shows that the Einstein Telescope can improve the constraints on the charge-to-mass-ratio to $Q\lesssim 0.2$ at 90% credible level with one ringdown signal.

Compact binaries with unequal masses and whose orbits are not aligned with the observer’s line of sight are excellent probes of gravitational radiation beyond the quadrupole approximation. Among the compact binaries observed so far, strong evidence of octupolar modes is seen in GW190412 and GW190814, two binary black holes observed during the first half of the third observing run of LIGO/Virgo observatories. These two events, therefore, provide a unique opportunity to test the consistency of the octupolar modes with the predictions of general relativity (GR). In the post-Newtonian (PN) approximation to GR, the gravitational-wave phasing has known dependencies on different radiative multipole moments, including the mass octupole. This permits the use of publicly released posteriors of the PN phase deformation parameters for placing constraints on the deformations to the different PN components of the radiative mass octupole denoted by $\delta {\mu }_{3n}$. Combining the posteriors on $\delta {\mu }_{3n}$ from these two events, we deduce a joint bound (at 90% credibility) on the first three PN order terms in the radiative octupoles to be $\delta {\mu }_{30}=-0.07_{-0.12}^{+0.11}$, $\delta {\mu }_{32}=0.48_{-1.15}^{+0.93}$, and $\delta {\mu }_{33}=-0.32_{-0.62}^{+1.67}$, consistent with GR predictions. Among these, the measurement of $\delta {\mu }_{33}$ for the first time confirms the well-known octupolar tail contribution, a novel nonlinear effect due to the scattering of the octupolar radiation by the background spacetime, is consistent with the predictions of GR. Detection of similar systems in the future observing runs should further tighten these constraints.

We present a model-independent reconstruction of the early expansion and thermal histories of the Universe, obtained from light element abundance measurements. The expansion history is tightly constrained around the onset of the big bang nucleosynthesis (BBN). The temperature of photons is additionally constrained around the time of neutrino decoupling. Allowing for perturbations to the standard expansion rate, we find that the radiation energy density is constrained to within 15% of its $\mathrm{\Lambda }\mathrm{CDM}$ value, and only 1% extra matter energy density is allowed around the epoch of BBN. We introduce a new and general analytic fitting formula for the temperature variation, which is flexible enough to reproduce the signal of large classes of beyond-CDM particle models that can alter the temperature through early-time energy injection. We present its constraints from BBN data and from the measurements of effective number of relativistic species and helium-4 abundance probed by the cosmic microwave background radiation anisotropy. Our results provide clarity on the most fundamental properties of the early Universe, reconstructed with minimal assumptions about the unknown physics that can occur at keV–MeV energy scales and can be mapped to broad classes of models of interest to cosmology.

The shear and interface modes excited inside the neutron star due to the presence of elasticity depend on the properties of both the crust and core region. To examine how such eigenfrequencies depend on the neutron star properties, we solve the eigenvalue problem by adopting the relativistic Cowling approximation. Then, we confirm that the number of the interface modes excited in the star is generally equivalent to the number of the interface where the shear modulus discontinuously becomes zero, but we also find that the number of interface modes becomes smaller than that of the interface for the stellar model with lower or higher value of the slope parameter $L$. Furthermore, we derive the empirical relations for expressing the shear modes and one of the interface modes, which is the mode whose amplitude becomes dominant at the interface between the crust and envelopes and at the interface between the phases of slablike and cylindrical nuclei. At the end, we also show the possibility of identifying the higher quasiperiodic oscillation frequencies observed in GRB 200415A with the shear oscillations, as an alternative possibility instead of the torsional oscillations.

The astrophysical stochastic gravitational wave background (SGWB) originates from numerous faint subthreshold gravitational wave (GW) signals arising from the coalescing binary compact objects. This background is expected to be discovered from the current (or next-generation) network of GW detectors by cross-correlating the signal between multiple pairs of GW detectors. However, detecting this signal is challenging and the correlation is only detectable at low frequencies due to the arrival time delay between different detectors. In this work, we propose a novel technique, Spectrogram Correlated Stacking (SpeCS), which goes beyond the usual cross-correlation (and to higher frequencies) by exploiting the higher-order statistics in the time-frequency domain which accounts for the chirping nature of the individual events that comprise SGWB. We show that SpeCS improves the signal-to-noise for the detection of SGWB by a factor close to 8, compared to standard optimal cross-correlation methods which are tuned to measure only the power spectrum of the SGWB signal. SpeCS can probe beyond the power spectrum and its application to the GW data available from the current and next-generation GW detectors would speed up the SGWB discovery.

We study the landscape of lower-dimensional vacua of the standard model (SM) coupled to gravity in the presence of the so-called “dark dimension” of size $R_{\perp }$ in the micron range, focusing on the validity of the swampland conjecture forbidding the presence of nonsupersymmetric anti–de Sitter (AdS) vacua in a consistent quantum gravity theory. We first adopt the working assumption that right-handed neutrinos propagate in the bulk, so that neutrino Yukawa couplings become tiny due to a volume suppression, leading to naturally light Dirac neutrinos. We show that the neutrino Kaluza-Klein (KK) towers compensate for the graviton tower to maintain stable de Sitter (dS) vacua found in the past, but neutrino oscillation data set restrictive bounds on $R_{\perp }$ and therefore the first KK neutrino mode is too heavy to alter the shape of the radion potential or the required maximum mass for the lightest neutrino to carry dS rather than AdS vacua found in the absence of the dark dimension, $m_{1,\max }\lesssim 7.63\mathrm{meV}$. We also show that a very light gravitino (with mass in the meV range) could help relax the neutrino mass constraint $m_{1,\max }\lesssim 50\mathrm{meV}$. The differences for the predicted total neutrino mass $\sum m_{\nu }$ among these two scenarios are within reach of next-generation cosmological probes that may measure the total neutrino mass with an uncertainty $\sigma (\sum m_{\nu })=0.014\mathrm{eV}$. We also demonstrate that the KK tower of a very light gravitino can compensate for the graviton tower to sustain stable dS vacua and thus right-handed neutrinos can (in principle) be locked on the brane. For this scenario, Majorana neutrinos could develop dS vacua, which is not possible in the SM coupled to gravity. Finally, we investigate the effects of bulk neutrino masses in suppressing oscillations of the zero modes into the first KK modes to relax the oscillation bound on $R_{\perp }$.

We investigate the $K_1(1270)-K_1(1400)$ mixing induced by the flavor $SU(3)$ symmetry breaking. The mixing angle is calculated in a purely theoretical manner, where it is expressed by a $K_{1A}\to K_{1B}$ transition matrix element of the operators that break flavor $SU(3)$ symmetry. The QCD contribution to this matrix element is assumed to be dominated and calculated with QCD sum rules. A three-point correlation function is defined and handled both at the hadron and quark-gluon levels. The quark-gluon level calculation is based on operator product expansion up to dimension-five condensates. A detailed numerical analysis is performed to determine the Borel parameters, and the obtained mixing angle is ${\theta }_{K_1}=21.4°\pm 9°$ or ${\theta }_{K_1}=68.6°\pm 9°$.

The triplet vector boson (TVB) is a simplified new physics model involving massive vector bosons transforming as a weak triplet vector. Such a model has been proposed as a combined explanation of the anomalous $b\to s{\mu }^{+}{\mu }^{-}$ and $b\to c\tau {\overline{\nu }}_{\tau }$ data (the so-called $B$ meson anomalies). In this work, we carry out a revamped view of the TVB model by incorporating the most recent 2022 and 2023 LHCb measurements on the lepton-flavor universality ratios $R(D^{(*)})=\mathrm{BR}(B\to D^{(*)}\tau {\overline{\nu }}_{\tau })/\mathrm{BR}(B\to D^{(*)}{\ell }^{\prime }{\overline{\nu }}_{{\ell }^{\prime }})$, $R({\mathrm{\Lambda }}_c)=\mathrm{BR}({\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c\tau {\overline{\nu }}_{\tau })/\mathrm{BR}({\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c\mu {\overline{\nu }}_{\mu })$, and $R_{K^{(*)}}=\mathrm{BR}(B\to K^{(*)}{\mu }^{+}{\mu }^{-})/\mathrm{BR}(B\to K^{(*)}{e}^{+}{e}^{-})$. We perform a global fit to explore the allowed parameter space by the new data and all relevant low-energy flavor observables including the recent experimental progress from Belle, Belle II, and LHCb. Our results are confronted with the recent high-mass dilepton searches at the LHC. We find that for a heavy TVB mass of 1 TeV a common explanation of the $B$ meson anomalies is possible for all data with the recent LHCb measurements on $R(D^{(*)})$, consistent with LHC constraints. However, this framework is in strong tension with LHC bounds when one considers all data along with the world average values reported by the Heavy Flavor Averaging Group (BABAR, Belle, and LHCb) on $R(D^{(*)})$. Future measurements will be required in order to clarify such a situation.

We show that the recent detection of a gravitational wave (GW) background reported by various pulsar timing array (PTA) collaborations including NANOGrav-15 yr, PPTA, EPTA/InPTA, and CPTA can be explained in terms of first order phase transitions (FOPTs) from dark sector models (DSM). Specifically, we explore a model for first order phase transitions that involves the Majoron, a Nambu-Goldstone boson that is emerging from the spontaneous symmetry breaking of a $U(1{)}_L$ or $U(1{)}_{B-L}$ symmetry. We show how the predicted GW power spectrum, with a realistic choice of the FOPT parameters, is consistent with $1\text{−}\sigma$ deviations from the estimated parameters of the background detected by the PTA collaborations.

The Brillouin action is a Wilson-like lattice fermion action with a 81-point stencil, which was found to ameliorate the Wilson action in many respects. The Sheikholeslami-Wohlert coefficient $c_{\mathrm{SW}}$ of the clover improvement term has a perturbative expansion $c_{\mathrm{SW}}=c_{\mathrm{SW}}^{(0)}+g_0^2{c}_{\mathrm{SW}}^{(1)}+\mathcal{O}(g_0^4)$. At tree-level $c_{\mathrm{SW}}^{(0)}=r$ holds for Wilson and Brillouin fermions alike. We present the Feynman rules for the Brillouin action in lattice perturbation theory, and employ them to calculate the one-loop coefficient $c_{\mathrm{SW}}^{(1)}$ with plaquette or Lüscher-Weisz gluons. Numerically its value is found to be about half that of the Wilson action.

We compute the $\sin (2\varphi -{\varphi }_S)$ azimuthal asymmetry in the pion-nucleon induced Drell-Yan process within transverse momentum dependent factorization. We employ the holographic light-front pion wave functions to calculate its leading-twist transverse momentum dependent parton distributions (TMDs). The Boer-Mulders TMD of the pion is then convoluted with the transversity TMD of the proton evaluated in a light-front quark-diquark model constructed with the wave functions predicted by the soft-wall AdS/QCD to obtain the azimuthal asymmetry in the Drell-Yan process. The gluon rescattering is pivotal to predict nonzero pion Boer-Mulders TMD. We investigate the utility of a nonperturbative SU(3) gluon rescattering kernel going beyond the usual approximation of perturbative U(1) gluons. The holographic light-front QCD approach provides a powerful tool for exploring the role of nonperturbative QCD effects in the Drell-Yan process and may help to guide future experimental measurements.

We discuss the possibility to obtain a massive Landau gauge, based on the local composite operator effective action framework combined with the Zimmermann reduction of couplings prescription. As a way to deal with the gauge ambiguity, we check that the ghost propagator remains positive, a necessary condition for gluon field configurations beyond the Gribov region to be negligible. We pay attention to the Becchi-Rouet-Stora-Tyutin invariance of the construction, allowing for a future generalization to a class of massive linear covariant gauges. As a litmus test, we compare our predictions to the lattice data for the two-point functions in Landau gauge introducing the “dynamically infrared-safe” renormalization scheme, including the renormalization group optimization of both the gap equation and the two-point functions. We also discuss the relation to and differences with the Curci-Ferrari model, the usefulness of which in providing an effective perturbative description of nonperturbative Yang-Mills theories became clear during recent years.

To study the light baryon light cone distribution amplitudes (LCDAs), the spatial correlator of the light baryon has been calculated up to one-loop order in coordinate space. They reveal certain identities that do not appear in the study of mesons DAs and parton distribution functions. Subsequently, it was renormalized using the ratio renormalization scheme involving division by a 0-momentum matrix element. Then through the matching in the coordinate space, the light baryon light cone correlator can be extracted out from the spatial correlator. These results provide insights into both the ultraviolet and infrared structures of the light baryon spatial correlator, which is valuable for further exploration in this field. Furthermore, the employed ratio scheme is an efficient and lattice-friendly renormalization approach suitable for short-distance applications. These can be used for studying the light baryon LCDAs using lattice techniques.