The understanding of the physical laws determining the infrared behavior of amplitudes is a longstanding and topical problem. In this paper, we show that energy conservation alone implies strong constraints on the threshold singularity structure of Feynman diagrams. In particular, we show that it implies a representation of loop integrals in terms of Fourier transforms of nonsimplicial convex cones. We then engineer a triangulation that has a direct diagrammatic interpretation in terms of a straightforward edge-contraction operation. We use it to develop an algorithmic procedure that performs the Fourier integrations in closed form, yielding the novel cross-free family three-dimensional representation of loop integrals. Its singularity structure is entirely and elegantly expressed in terms of the graph-theoretic notions of connectedness and crossing. These results can be used to study the Kinoshita-Lee-Nauenberg cancellation mechanism, numerically evaluate loop integrals and to simplify threshold regularization procedures.

String geometry theory is one of the candidates for a nonperturbative formulation of string theory. In this paper, from the string geometry theory, we derive path integrals of perturbative superstrings on all string backgrounds, $G_{\mu \nu }(x)$ and $B_{\mu \nu }(x)$, by considering fluctuations around the string background configurations, which are parametrized by the string backgrounds.

We present a generalization of the embedding space formalism to conformal field theories (CFTs) on nontrivial states and curved backgrounds, based on the ambient metric of Fefferman and Graham. The ambient metric is a Lorentzian Ricci-flat metric in $d+2$ dimensions and replaces the Minkowski metric of the embedding space. It is canonically associated with a $d$-dimensional conformal manifold, which is the physical spacetime where the ${\mathrm{CFT}}_d$ lives. We propose a construction of ${\mathrm{CFT}}_d$ $n$-point functions in nontrivial states and on curved backgrounds using appropriate geometric invariants of the ambient space as building blocks. This captures the contributions of nonvanishing one-point functions of multi-stress-energy tensors, at least in holographic CFTs. We apply the formalism to two-point functions of thermal CFT, finding exact agreement with a holographic computation and expectations based on thermal operator product expansions (OPEs), and to CFTs on squashed spheres where no prior results are known and existing methods are difficult to apply, demonstrating the utility of the method.

We investigate the mutual information harvesting protocol for two uniformly accelerated particle detectors. We numerically show that, while a single detector responds as if it is immersed in a thermal bath, the quantum mutual information between two accelerating detectors behaves differently than that of two inertial detectors in a thermal bath. This is due to the fact that while the Wightman function along the trajectory of a single uniformly accelerating detector is the same as that of a detector in a thermal bath, a pair of detectors in the same respective cases will have different Wightman functions.

The classical Lagrangian of the Standard Model enjoys the symmetry of the full conformal group if the mass of the Higgs boson is put to zero. This is a hint that conformal symmetry may play a fundamental role in the ultimate theory describing nature. The origin of scales, such as the Higgs vacuum expectation value (VEV), may result from the spontaneous breakdown of the conformal symmetry by the dilaton field. In this work, we study whether this classical setup can be implemented in quantum theory and be phenomenologically viable by presenting an explicit construction where the exact conformal symmetry can be preserved and is anomaly-free while being spontaneously broken. Not only the Higgs mass but also the genuine quantum scales such as the QCD confinement radius are generated by the dilaton VEV. We also discuss the extension of these ideas to the theories with dynamical gravity and show that the only finite subgroup of the local Weyl transformations which is anomaly-free corresponds to the global scale symmetry. This means that the conformal invariance of the flat space theory is explicitly broken down to the scale symmetry by gravitational effects related to the Weyl anomaly.

We reconsider the gravitational wave spectrum induced by scalar perturbations in spatially flat Friedmann-Lemaître-Robertson-Walker spacetimes, focusing on the matter- and $\mathrm{\Lambda }$-dominated epochs. During matter domination, subhorizon modes are not free, and a commonly applied approximation for the derivative of the tensor perturbation is flawed. We show analytically that this leads to a significant overestimation of the energy density spectrum. In addition, we demonstrate that gauge-dependent nonoscillating tensor perturbations appear in the presence of a cosmological constant. Complementing the analytical calculations, we compute the according present-day spectrum numerically for a Planck-like $\mathrm{\Lambda }\mathrm{CDM}$ cosmology, finding that nonoscillating growing modes appear during the transition between matter and $\mathrm{\Lambda }$ domination in conformal Newtonian gauge.

We construct a model explaining dark matter, baryon asymmetry, and reheating in a quintessential inflation model. Three generations of right-handed neutrinos having hierarchical masses and the light scalar field leading to the self-interaction of active neutrinos are introduced. The lightest sterile neutrino is a dark matter candidate produced by a Dodelson-Widrow mechanism in the presence of a new light scalar field, while the heaviest and next-heaviest sterile neutrinos produced by gravitational particle production are responsible for the generation of the baryon asymmetry. Reheating is realized by spinodal instabilities of the Standard Model Higgs field induced by the nonminimal coupling to the scalar curvature, which can solve the overproduction of gravitons and curvature perturbation created by the Higgs condensation.

Neutron star mergers have recently become a tool to study extreme gravity, nucleosynthesis, and the chemical composition of the Universe. To date, there has been one joint gravitational and electromagnetic observation of a binary neutron star merger, GW170817, as well as a solely gravitational observation, GW190425. In order to accurately identify and interpret electromagnetic signals of neutron star mergers, better models of the matter outflows generated by these mergers are required. We compare a series of ejecta models to see where they provide strong constraints on the amount of ejected mass expected from a system, and where systematic uncertainties in current models prevent us from reliably extracting information from observed events. We also examine 2396 neutron star equations of state compatible with GW170817 to see whether a given ejecta mass could be reasonably produced with a neutron star of said equation of state, and whether different ejecta models provide consistent predictions. We find that the difference between models is often comparable to or larger than the error generally assumed for these models, implying better constraints on the models are needed. We also note that the extrapolation of outflow models outside of their calibration window, while commonly needed to analyze gravitational wave events, is extremely unreliable and occasionally leads to completely unphysical results.

We describe a novel approach to the detection and parameter estimation of a non-Gaussian stochastic background of gravitational waves. The method is based on the determination of relevant statistical parameters using importance sampling. We show that it is possible to improve the Gaussian detection statistics by simulating realizations of the expected signal for a given model. While computationally expensive, our method improves the detection performance, leveraging the prior knowledge on the expected signal, and can be used in a natural way to extract physical information about the background. We present the basic principles of our approach, characterize the detection statistic performances in a simplified context, and discuss possible applications to the detection of some astrophysical foregrounds. We argue that the proposed approach, complementarily to the ones available in literature might be used to detect suitable astrophysical foregrounds by currently operating and future gravitational wave detectors.

Deviations from the Standard Model (SM) can be parametrized in terms of the SM effective field theory (SMEFT), which is typically truncated at dimension-6. Including higher dimension operators—as well as considering simultaneous insertions of multiple dimension-6 operators—may be necessary in some processes, in order to correctly capture the properties of the underlying UV theory. As a step toward clarifying this in the Higgs boson production in gluon fusion process, we study double insertions of dimension-6 operators in the 1-loop virtual amplitude. We present needed Feynman rules up to $\mathcal{O}(1/{\mathrm{\Lambda }}^4)$ and we numerically study the impact of various approximations to the $\mathcal{O}(1/{\mathrm{\Lambda }}^4)$ expansion.

A phenomenological study for determining the chirality structure in lepton-flavor-violating Higgs decays $h\to \tau \mu$ at the LHC is presented. We estimate the effects of the $\tau$ polarization in the analysis and the importance of determining the relative visible momentum ratio $x$, and show the analysis with a collinear mass $m_{\mathrm{col}1}$ by assuming one missing particle is appropriate. We find that the sensitivity would be generically affected up to $\pm 4–6\%$ in terms of the $\mathrm{BR}(h\to \tau \mu )$ upper bound, and show the altered bounds on the $(|y_{\mu \tau }|,|y_{\tau \mu }|)$ plane. We further study the benchmark scenarios, and demonstrate the sensitivity study for the chirality structure using the relative visible momentum ratio. We find that the two fully polarized cases, the ${\tau }_R$ and ${\tau }_L$ scenarios consistent with the recently reported excess, are distinguishable at $2\sigma$ level for $1000{\mathrm{fb}}^{-1}$. We also show that a further improved study potentially provides a similar sensitivity already for $139{\mathrm{fb}}^{-1}$.

In this study, the strong coupling constants of the unobserved heavy axial tensor mesons to the heavy vector and pseudoscalar $\pi$ and $K$ mesons, $D_2{D}^{*}\pi$, $D_{s2}{D}^{*}K$, $B_2{B}^{*}\pi$, $B_{s2}{B}^{*}K$ as well as a heavy axial tensor to axial vector and light pseudoscalar $\pi$ and $K$-mesons, $D_2{D}_1\pi$, $D_{s2}{D}_{1}K$, $B_2{B}_1\pi$, $B_{s2}{B}_{1}K$ vertices have been investigated within the light cone QCD sum rules method. Having obtained the strong coupling constants, we estimate the corresponding decay widths that will hopefully be verified in future experiments.

QCD matrix elements of axial and vector currents between nucleons are required for the Monte Carlo reconstruction of the energy of neutrinos that are detected in long baseline oscillation experiments in the quasielastic regime. The cleanest approach for determining the axial matrix elements is lattice QCD. However, the extraction of these from the corresponding correlation functions is complicated by very large excited state contributions, that are related to transitions from the nucleon to a nucleon-pion pair. In this pilot study with a pion mass $m_{\pi }=429\mathrm{MeV}$, we demonstrate for the first time that these contributions can be removed by including five-(anti)quark operators into the basis of interpolators used to create the nucleon. The same techniques will be needed to compute transition matrix elements between the nucleon and nucleon-pion scattering states that are relevant in the resonance production regime.

Search sensitivity to a stochastic gravitational-wave background (SGWB) is enhanced by cross-correlating detector signals. However, one of the most serious concerns is the environmental noise correlated between detectors. The global electromagnetic fields on the Earth, known as Schumann resonances, produce the correlated noise through the instrumental magnetic couplings. In this paper, we study the detectability of a SGWB in the presence of the correlated magnetic noise, using the Fisher analysis based on the analytical model of the correlated magnetic noise. We find that there is no significant degeneracy between the SGWB and noise parameters. Marginalizing over the correlated noise parameters degrades the constraint on each SGWB parameter by a factor of $\sim 2$ at most in the four-detector case, irrespective of the strength of the magnetic coupling. We also confirm that the forecast results are robust against the variation of correlated noise parameters and can vary up to 40% in the realistic range of the coupling parameters for the second-generation detectors. However, ignoring the correlated noise in parameter estimation generally leads to a biased constraint on the SGWB parameters. If the coupling strength is twice as large as expected, this could result in a serious bias.

We investigate the generation rate of quantum gravity induced entanglement of masses (QGEM) in setups with multiple quantum massive particles, among which only the gravity interaction due to the Newton potential is taken into account. When the distance between any two adjacent Stern-Gerlach devices is fixed, we consider all the possible configurations of the setup with the same number of particles. In particular, we systemically analyze the case of particle number $n=4$ and find that the prism setup with a massive particle at the center is the most efficient setup for the entanglement generation. This result can be extended to a system with multiple particles up to seven, where the entanglement efficiency is also enhanced in comparison with the setup with fewer particles. This work provides the strategy to construct the quantum gravity induced entanglement of masses setup with the best generation rate of entanglement.

The stability of a class of electrically charged fluid spheres under radial perturbations is studied in this work. Among these spheres there are regular stars, overcharged tension stars, regular black holes, quasiblack holes, and quasinonblack holes, all of which have a Reissner-Nordström exterior. We formulate the dynamical perturbed equations by following the Chandrasekhar approach and investigate the stability against radial perturbations through numerical methods. It is found that (i) under certain conditions that depend on the adiabatic index of the radial perturbation, there are stable charged stars and stable tension stars; (ii) also depending on the adiabatic index there are stable regular black holes; (iii) quasiblack hole configurations formed by, e.g., charging regular pressure stars or by discharging regular tension stars, can be stable against radial perturbations for reasonable values of the adiabatic index; and (iv) quasinonblack holes are unstable against radial perturbations.