In this paper, infrared regularization of semi-infinite entangling regions and island formation for regions of finite size in the eternal Schwarzschild black hole are considered. We analyze whether the complementarity property and pure state condition of entanglement entropy can be preserved in the given approximation. We propose a special regularization that satisfies these two properties. With regard to entangling regions of finite size, we derive two fundamental types of them, which we call “mirror-symmetric” (MS) and “asymmetric” (AS). For MS regions, we discover a discontinuous evolution of the entanglement entropy of Hawking radiation due to finite lifetime of the island. The entanglement entropy of matter for semi-infinite regions in two-sided Schwarzschild black hole does not follow the Page curve. The lifetime of AS regions is bounded from above due to the phenomenon that we call “Cauchy surface breaking.” Shortly before this breaking, the island configuration becomes nonsymmetric. For both types of finite regions, there is a critical size, below which the island never dominates. For regions smaller than some other critical size, the island does not emerge. Finally, we show that the island prescription does not help to solve the information paradox for certain finite regions.

More than twenty years ago a paradigm emerged according to which a UV-insensitive Higgs mass $m_H$ and (more generally) a UV-insensitive Higgs effective potential $V_{1l}(\varphi )$ are obtained from higher-dimensional theories with compact extra dimensions and Scherk-Schwarz supersymmetry breaking. Since then, these ideas have been applied to different models of phenomenological interest, including recent applications to the dark energy problem. A thorough analysis of the framework on which such a paradigm is based allows us to show that a source of strong UV sensitivity for $m_H$ and $V_{1l}(\varphi )$, intimately connected to the nontrivial topology of these models’ spacetime, was missed. The usual picture of the Scherk-Schwarz mechanism and its physical consequences need to be seriously reconsidered.

A real scalar field coupled to a fermion via a Yukawa term can evade no-go theorems preventing solitonic solutions. For the first time, we study this model within general relativity without approximations, finding static and spherically symmetric solutions that describe fermion soliton stars. The Yukawa coupling provides an effective mass for the fermion, which is key to the existence of self-gravitating relativistic solutions. We systematically study this novel family of solutions and present their mass-radius diagram and maximum compactness, which is close to (but smaller than) that of the corresponding Schwarzschild photon sphere. Finally, we discuss the ranges of the parameters of the fundamental theory in which the latter might have interesting astrophysical implications, including compact (sub)solar and supermassive fermion soliton stars for a standard gas of degenerate neutrons and electrons, respectively.

Astrophysical observations of neutron stars probe the structure of dense nuclear matter and have the potential to reveal phase transitions at high densities. Most recent analyses are based on parametrized models of the equation of state with a finite number of parameters and occasionally include extra parameters intended to capture phase-transition phenomenology. However, such models restrict the types of behavior allowed and may not match the true equation of state. We introduce a complementary approach that extracts phase transitions directly from the equation of state without relying on, and thus being restricted by, an underlying parametrization. We then constrain the presence of phase transitions in neutron stars with astrophysical data. Current pulsar mass, tidal deformability, and mass-radius measurements disfavor only the strongest of possible phase transitions (latent energy per particle $\gtrsim 100\mathrm{MeV}$). Weaker phase transitions are consistent with observations. We further investigate the prospects for measuring phase transitions with future gravitational-wave observations and find that catalogs of $O(100)$ events will (at best) yield Bayes factors of $\sim 10:1$ in favor of phase transitions even when the true equation of state contains very strong phase transitions. Our results reinforce the idea that neutron star observations will primarily constrain trends in macroscopic properties rather than detailed microscopic behavior. Fine-tuned equation of state models will likely remain unconstrained in the near future.

I investigate the sensitivity of gravitational-wave searches by analyzing the response of matched filters in stationary Gaussian noise. In particular, I focus on the ability to analytically model the distribution of observed filter responses maximized over coalescence phase and/or a template bank as well as the response of statistics defined for a network of detectors. Semianalytic sensitivity estimates derived assuming stationary Gaussian noise are compared to sensitivity estimates obtained from real searches processing real noise, which is neither perfectly stationary nor perfectly Gaussian. I find that semianalytic estimates are able to reproduce real search sensitivity for the LIGO-Virgo-KAGRA Collaboration’s third observing run with high fidelity. I also discuss how to select computational speed-ups (hopeless signal-to-noise ratio cuts) and make predictions for the fourth observing run using projected detector sensitivities.

Next-generation ground-based gravitational-wave detectors, such as Cosmic Explorer (CE), are expected to be sensitive to gravitational-wave signals with frequencies as low as 5 Hz, allowing signals to spend a significant amount of time in the detector frequency band. As a result, the effects caused by the rotation of the Earth become increasingly important for such signals. Additionally, the length of the arms of these detectors can be comparable to the wavelength of detectable gravitational waves, which introduces frequency-dependent effects that are not significant in current-generation detectors. These effects are expected to improve the ability to localize compact binary coalescences in the sky even when using only one detector. This study aims to understand how much these effects can help in localization. We present the first comprehensive Bayesian parameter estimation framework that accounts for all of these effects using bilby, a commonly used Bayesian parameter estimation tool. We focus on sky localization constraints for binary neutron star events with an optimal signal-to-noise ratio of 1000 with one detector at the projected CE sensitivity. We find that these effects help localize sources using one detector with sky areas as low as 10 square degrees. Moreover, we explore and discuss how ignoring these effects in the parameter estimation can lead to biases in the inference.

We demonstrate a new geometric method for fast template placement for searches for gravitational waves from the inspiral, merger and ringdown of compact binaries. The method is based on a binary tree decomposition of the template bank parameter space into nonoverlapping hypercubes. We use a numerical approximation of the signal overlap metric at the center of each hypercube to estimate the number of templates required to cover the hypercube and determine whether to further split the hypercube. As long as the expected number of templates in a given cube is greater than a given threshold, we split the cube along its longest edge according to the metric. When the expected number of templates in a given hypercube drops below this threshold, the splitting stops and a template is placed at the center of the hypercube. Using this method, we generate aligned-spin template banks covering the mass range suitable for a search of Advanced LIGO, Advanced Virgo and KAGRA data. The aligned-spin bank was generated in $\sim 24\mathrm{hours}$ using a single CPU core and produced 2 million templates. Our primary motivation for developing this algorithm is to produce a bank with useful geometric properties in the physical parameter space coordinates. Such properties are useful for population modeling and parameter estimation.

In this study, we calculate the sensitivity reach on the vector leptoquark (LQ) $U_1$ at the experiments proposed in the Forward Physics Facility (FPF), including $\mathrm{FASER}\nu$, $\mathrm{FASER}\nu 2$, FLArE (10 tons), and FLArE (100 tons) using the neutrino-nucleon scattering ($\nu N\to \nu N^{\prime }$ and $\nu N\to l{N}^{\prime }$). We cover a wide mass range of ${10}^{-3}\mathrm{GeV}\le M_{\mathrm{LQ}}\le {10}^4\mathrm{GeV}$. The new result shows that the FLArE (100 tons) offers the best sensitivity to the LQ model. The sensitivity curves for all the experiments follow a similar pattern with weakened sensitivities with the increment of the LQ mass. We combine the sensitivities obtained from the neutral- and charged-current interactions of the neutrinos.

Long-baseline atom interferometers offer an exciting opportunity to explore midband gravitational waves with frequencies of 1 mHz–10 Hz. In this work we survey the landscape of possible contributions to the total gravitational wave background from merging binary systems in this frequency band and advocate for targeting this observable. Such an approach is complimentary to searches for resolved mergers from individual sources and may have much to reveal about the Universe. We highlight that the inspiral phases of known stellar-mass compact binaries cumulatively produce a signal well within reach of the proposed AION-km and AEDGE experiments which will need to be accounted for in the gravitational wave programs of these experiments. We further show that hypothetical populations of dark sector exotic compact objects, harboring just a tiny fraction of the dark energy density, could generate signatures unique to gravitational wave detectors sensitive to subhertz frequencies, providing a novel means to probe complexity in the dark sector.

Vectorial partners of the Standard Model quarks and leptons are predicted in many dynamical models of electroweak symmetry breaking. The most easily accessible of these new particles, either due to mass or couplings, are typically expected to be the partners of the third-generation fermions. It is therefore essential to explore the signatures of these particles at future high-energy colliders. We study the potential of a high-energy muon collider to singly produce a vectorlike top-quark partner via an electroweak dipole moment operator, such an operator being typical of composite constructions beyond the Standard Model. We use a phenomenological model for third-generation quarks and their partners that satisfies an extended custodial symmetry. This automatically protects the $W$-boson and $Z$-boson masses from receiving large electroweak corrections, and it allows the model to be viable given current electroweak data. We demonstrate that cross sections associated with dipole-induced vectorlike quark production can easily exceed those inherent to more conventional single-production modes via ordinary electroweak couplings. We then explore the associated phenomenology, and we show that at least one (and often more than one) of the extra vectorlike states can be studied at high-energy muon colliders. Typical accessible masses are found to range up to close to the kinematic production threshold, when the vectorlike partners are produced in combination with an ordinary top quark.

We demonstrate that a state-of-the-art multigrid preconditioner can be learned efficiently by gauge-equivariant neural networks. We show that the models require minimal retraining on different gauge configurations of the same gauge ensemble and to a large extent remain efficient under modest modifications of ensemble parameters. We also demonstrate that important paradigms such as communication avoidance are straightforward to implement in this framework.

We compute the gravitational form factor $D(t)$ of various nuclei in the generalized Skyrme model where nuclei are described as solitonic field configurations each with a definite baryon number $B$. We separately discuss the cases $B=1$ (nucleons), $B=2$ (deuteron), $B=3$ (helium-3 and tritium), and extrapolate to larger $B$-values. Configurations with $B>1$ are in general not spherically symmetric, and we demonstrate how group theory helps to extract the form factor. Numerical results are presented for the configurations with $B=1,2,3,4,5,6,7,8$, 32, 108. We find that the $B$-dependence is consistent with a power-law $D(0)\propto B^{\beta }$ with $\beta =1.7–1.8$. Other gravitational form factors can be calculated in the same framework, and we show the result for the $J(t)$ form factor associated with the angular momentum for the $B=3$ solution.

In a previous work by one of the authors, it was demonstrated that the discrepancy between the fixed-order and contour-improved (CIPT) perturbative expansions for $\tau$-lepton decay hadronic spectral function moments, which had been affecting the precision of ${\alpha }_s$ determinations for many years, is related to the CIPT expansion being inconsistent with the standard formulation of the operator product expansion. Even though the problem can be alleviated phenomenologically for the most part by employing a renormalon-free scheme for the gluon-condensate matrix element, the principal inconsistency of CIPT remains. The CIPT expansion is special because it is not a power expansion, but represents an asymptotic expansion in a sequence of functions of the strong coupling. In this article we provide a closer look at the mathematical aspects of the asymptotic sequence of the functions the CIPT method is based on, and we expose the origin of the CIPT inconsistency as well as the reasons for its apparent good convergence at low orders. Our results are of general interest, and may in particular provide a useful tool to check for the consistency of expansion methods that are similar to CIPT.

The production of a $W$ boson in association with a single charm quark is studied using $140{\mathrm{fb}}^{-1}$ of $\sqrt{s}=13\mathrm{TeV}$ proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. The charm quark is tagged by the presence of a charmed hadron reconstructed with a secondary-vertex fit. The $W$ boson is reconstructed from the decay to either an electron or a muon and the missing transverse momentum present in the event. The charmed mesons reconstructed are $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$ and $D^{*+}\to D^0{\pi }^{+}\to (K^{-}{\pi }^{+}){\pi }^{+}$ and the charge conjugate decays in the fiducial regions where $p_{\mathrm{T}}(e,\mu )>30\mathrm{GeV}$, $|\eta (e,\mu )|<2.5$, $p_{\mathrm{T}}(D^{(*)})>8\mathrm{GeV}$, and $|\eta (D^{(*)})|<2.2$. The integrated and normalized differential cross sections as a function of the pseudorapidity of the lepton from the $W$ boson decay, and of the transverse momentum of the charmed hadron, are extracted from the data using a profile likelihood fit. The measured total fiducial cross sections are ${\sigma }_{\mathrm{fid}}^{\mathrm{OS}–\mathrm{SS}}(W^{-}+D^{+})=50.2\pm 0.2{(\mathrm{stat})}_{-2.3}^{+2.4}(\mathrm{syst})\mathrm{pb}$, ${\sigma }_{\mathrm{fid}}^{\mathrm{OS}–\mathrm{SS}}(W^{+}+D^{-})=48.5\pm 0.2{(\mathrm{stat})}_{-2.2}^{+2.3}(\mathrm{syst})\mathrm{pb}$, ${\sigma }_{\mathrm{fid}}^{\mathrm{OS}–\mathrm{SS}}(W^{-}+D^{*+})=51.1\pm 0.4{(\mathrm{stat})}_{-1.8}^{+1.9}(\mathrm{syst})\mathrm{pb}$, and ${\sigma }_{\mathrm{fid}}^{\mathrm{OS}–\mathrm{SS}}(W^{+}+D^{*-})=50.0\pm 0.4{(\mathrm{stat})}_{-1.8}^{+1.9}(\mathrm{syst})\mathrm{pb}$. Results are compared with the predictions of next-to-leading-order quantum chromodynamics calculations performed using state-of-the-art parton distribution functions. Additionally, the ratio of charm to anticharm production cross sections is studied to probe the $s\text{−}\overline{s}$ quark asymmetry. The ratio is found to be $R_c^{\pm }=0.971\pm 0.006(\mathrm{stat})\pm 0.011(\mathrm{syst})$. The ratio and cross-section measurements are consistent with the predictions obtained with parton distribution function sets that have a symmetric $s\text{−}\overline{s}$ sea, indicating that any $s\text{−}\overline{s}$ asymmetry in the Bjorken-$x$ region relevant for this measurement is small.

The spins of the pentaquark states $P_c(4440)$ and $P_c(4457)$ play a decisive role in unraveling their nature, but remain undetermined experimentally. Assuming that they are ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$ bound states, we demonstrate how one can determine their spins by measuring the ${\mathrm{\Sigma }}_c^{+}{\overline{D}}^{(*)0}$ correlation functions. We show that one can use the ${\mathrm{\Sigma }}_c^{+}{\overline{D}}^0$ correlation function to fix the size of the Gaussian source and then determine the strength of the ${\mathrm{\Sigma }}_c^{+}{\overline{D}}^{*0}$ interaction of spin $1/2$ and $3/2$ and therefore the spins of the $P_c(4440)$ and $P_c(4457)$ states. The method proposed can be applied to decipher the nature of other hadronic molecules and thus deepen our understanding of the nonperturbative strong interaction.

We analyze the fixed points of QCD at high loop order in a variety of renormalization schemes and gauges across the conformal window. We observe that in the minimal momentum subtraction scheme solutions for the Banks-Zaks fixed point persist for values of $N_f$ below that of the $\overline{\mathrm{MS}}$ scheme in the canonical linear covariant gauge. By treating the parameter of the linear covariant gauge as a second coupling constant we confirm the existence of a second Banks-Zaks twin critical point, which is infrared stable, to five loops. Moreover a similar and parallel infrared stable fixed point is present in the Curci-Ferrari and maximal Abelian gauges which persists in different schemes including kinematic ones. We verify that with the increased available loop order, critical exponent estimates show an improvement in convergence and agreement in the various schemes.

Gravitational parity violation arises in a variety of theories beyond general relativity. Gravitational waves in such theories have their propagation altered, leading to birefringence effects in both the amplitude and speed of the wave. In this work, we introduce a generalized, theory-motivated parametrization scheme to study parity violation in gravitational wave propagation. This parametrization maps to parity-violating gravity theories in a straightforward way. We find that the amplitude and velocity birefringence effects scale with an effective distance measure that depends on how the dispersion relation is modified. Furthermore, we show that this generic parametrization can be mapped to the parametrized-post-Einsteinian (ppE) formalism with convenient applications to gravitational wave observations and model-agnostic tests of general relativity. We derive a mapping to the standard ppE waveform of the gravitational wave response function, and also find a ppE waveform mapping at the level of the polarization modes, $h_{+}$ and $h_{\times }$. Finally, we show how existing constraints in the literature translate to bounds on our new parity-violating parameters and discuss avenues for future analysis.

Various groups recently demonstrated that the time evolution of the simplest self-interacting vector fields, those with self-interaction potentials, can break down after a finite duration in what is called loss of hyperbolicity. We establish that this is not an isolated issue, and other generalizations of the Proca theory suffer from the same problem. Specifically, we show that vector field theories with derivative self-interactions have a similar pathology. For this, we derive the effective metric that governs the dynamics, and show that it can change signature during time evolution. We also show that, generalized Proca theories may suffer from tachyonic instabilities as well, which lead to another form of unphysical behavior.