Light-cone gauge-fixed sigma models on ${\mathrm{AdS}}_n\times S^n$ backgrounds play an important role in the integrability formulation of the $\mathrm{AdS}/\mathrm{CFT}$ correspondence. The string spectrum of the sigma model is gauge independent, however the Hamiltonian and scattering matrix of the transverse world sheet fields are not. We study how these change for a large family of inequivalent light-cone gauges, which are interpreted as $T\overline{T}$, $\tilde{J}{T}_{\tau }$, $J{T}_{\sigma }$, and $J^{\tau }$ deformations. We investigate the moduli space of inequivalent light-cone gauges and, specializing to ${\mathrm{AdS}}_5\times S^5$, compute the different light-cone gauge symmetry algebras, well known to be $\mathfrak{psu}(2|2{)}^{\oplus 2}\oplus \mathfrak{u}(1{)}^{\oplus 2}$ for the standard gauge-fixing. Many integrable deformations require a nonstandard light-cone gauge, hence our classification and analysis of inequivalent gauges will be important for analyzing such models.

We investigate spherically symmetric axion stars with minimal coupling between a complex scalar field and gravity in a tidal environment. Tidal perturbations are treated as linear, and we calculate the tidal Love numbers for axion stars. The results show that the electric Love numbers of axion stars are positive, while the magnetic Love numbers are negative on the stable branch. The electric tidal Love numbers are much larger than the magnetic ones on the Newtonian stable branch, but only slightly larger on the relativistic stable branch. The relativistic stable branch has much smaller tidal Love numbers than the Newtonian stable branch, indicating weaker deformability of axion stars on the relativistic stable branch. This is due to the fact that axion stars are more compact on the relativistic branch, and thus hardly distorted by tidal forces.

Hunting compact astrophysical objects such as black holes and wormholes, as well as testing gravity theories, are important issues in relativistic astrophysics. In this sense, theoretical and observational studies of quasiperiodic oscillations (QPOs) observed in (micro)quasars become helpful in exploring their central object, which can be a black hole or a wormhole. In the present work, we study the throat properties of traversable wormholes beyond Horndeski theory. Also, we investigate the circular motion of test particles orbiting the wormhole. We analyze the test particle’s effective potential and angular momentum for circular orbits. Frequencies of radial and vertical oscillations of the particles around stable circular orbits have also been studied and applied in explaining the quasiperiodic oscillations mechanism in the relativistic precession (RP) model. Finally, we obtain constraint values for the parameters of beyond Horndeski gravity and the mass of the wormhole candidates using QPOs observed in the microquasars GRO J1655-40, GRS $1915+105$ & XTE J1550-564 and at the center of Milky Way galaxy through Monte-Carlo-Markovian-chain (MCMC) analyses.

The origin of the high-energy astrophysical neutrinos discovered by IceCube remains largely unknown. Multimessenger studies have indicated that the majority of these neutrinos come from gamma-ray-dark sources. Choked-jet supernovae (cjSNe), which are supernovae powered by relativistic jets stalled in stellar materials, may lead to neutrino emission via photohadronic interactions while the coproduced gamma rays are absorbed. In this paper, we perform an unbinned maximum-likelihood analysis to search for correlations between IceCube’s ten-year muon-track events and our SN $\mathrm{Ib}/\mathrm{c}$ sample, collected from publicly available catalogs. In addition to the conventional power-law models, we also consider the impacts of more realistic neutrino emission models for the first time, and we study the effects of the jet beaming factor in the analyses. Our results show no significant correlation. Even so, the conservative upper limits we set to the contribution of cjSNe to the diffuse astrophysical neutrino flux still allow SNe $\mathrm{Ib}/\mathrm{c}$ to be the dominant source of astrophysical neutrinos observed by IceCube. We discuss implications to the cjSNe scenario from our results and the power of future neutrino and supernova observations.

In dense neutrino gases, the neutrino-neutrino coherent forward scattering gives rise to a complex flavor oscillation phenomenon not fully incorporated in simulations of neutron star mergers (NSM) and core collapse supernovae (CCSNe). Moreover, it has been proposed to be chaotic, potentially limiting our ability to predict neutrino flavor transformations in simulations. To address this issue, we explore how small flavor perturbations evolve in the nonlinear regime of the neutrino quantum kinetic equation within a narrow centimeter-scale region inside a NSM and a toy neutrino distribution. Our findings reveal that paths in the flavor state space of solutions with similar initial conditions diverge exponentially, exhibiting chaos. This inherent chaos makes the microscopic scales of neutrino flavor transformations unpredictable. However, the domain-averaged neutrino density matrix remains relatively stable, with chaos minimally affecting it. This particular property suggests that domain-averaged quantities remain reliable despite the exponential amplification of errors.

We discuss an $SU(5)$ grand unified theory based on the $10d$ orbifold $({\mathbb{T}}^2{)}^3/({\mathbb{Z}}_4\times {\mathbb{Z}}_2)$ plus three modular $S_4$ groups with moduli at respective fixed points $i,i+2,\omega =e^{2i\pi /3}$. The resulting model has hierarchical quark and charged-lepton mass matrices, arising from a double weighton mechanism, and reproduces the highly predictive littlest seesaw mechanism in the neutrino sector. The down-quark mass matrix has an upper triangular form, contributing to Cabibbo-Kobayashi-Maskawa mixing, while the charged-lepton mass matrix has a lower-triangular form with suppressed contributions to Pontecorvo-Maki-Nakagawa-Sakata mixing. The orbifold yields successful $SU(5)$ breaking with doublet-triplet splitting of the Higgs multiplets.

The lightest supersymmetric particles could be Higgsinos that have a small mixing with gauginos. If the lightest Higgsino-like state makes up some or all of the dark matter with a thermal freeze-out density, then its mass must be between about 100 GeV and 1150 GeV, and dark matter searches put bounds on the amount of gaugino contamination that it can have. Motivated by the generally good agreement of flavor- and $CP$-violating observables with Standard Model predictions, I consider models in which the scalar particles of minimal supersymmetry are heavy enough to be essentially decoupled, except for the 125 GeV Higgs boson. I survey the resulting purity constraints as lower bounds on the gaugino masses and upper bounds on the Higgsino mass splittings. I also discuss the mild excesses in recent soft lepton searches for charginos and neutralinos at the LHC, and show that they can be accommodated in these models if $\tan \beta$ is small and $\mu$ is negative.

The recent observation of coherent elastic neutrino-nucleus scattering ($\mathrm{CE}\nu \mathrm{NS}$) with neutrinos from pion decay at rest ($\pi$-DAR) sources by the COHERENT Collaboration has raised interest in this process in the search for new physics. Unfortunately, current uncertainties in the determination of nuclear parameters relevant to those processes can hide new physics effects. This is not the case for processes involving lower-energy neutrino sources such as nuclear reactors. Note, however, that a $\mathrm{CE}\nu \mathrm{NS}$ measurement with reactor neutrinos depends largely on a (still-missing) precise determination of the quenching factor at very low energies, making its observation more challenging. In the upcoming years, once this signal is confirmed, a combined analysis of $\pi$-DAR and reactor $\mathrm{CE}\nu \mathrm{NS}$ experiments will be very useful to probe particle and nuclear physics, with a reduced dependence on nuclear uncertainties. In this work, we explore this idea by simultaneously testing the sensitivity of current and future $\mathrm{CE}\nu \mathrm{NS}$ experiments to neutrino nonstandard interactions (NSIs) and the neutron root mean square (rms) radius, considering different neutrino sources as well as several detection materials. We show how the interplay between future reactor and accelerator $\mathrm{CE}\nu \mathrm{NS}$ experiments can help to get robust constraints on the neutron rms and to break degeneracies between the NSI parameters. Our forecast could be used as a guide to optimize the experimental sensitivity to the parameters under study.

We investigate the potential of future tau neutrino experiments for identifying the ${\nu }_{\tau }$ appearance in probing secret neutrino interactions, which is very important in a variety of fields, such as neutrino physics, dark matter physics, grand unified theories, astrophysics, and cosmology. The reference experiments include the DUNE far detector utilizing the atmospheric data, which is for the first time probing secret interactions, the Forward Liquid Argon Experiment (FLArE100) detector at the Forward Physics Facility, and emulsion detector experiments such as SND@LHC, $\mathrm{FASER}\nu$, AdvSND, $\mathrm{FASER}\nu 2$, and SND@SHiP. For concreteness, we consider a reference scenario in which the hidden interactions among the neutrinos are mediated by a single light gauge boson $Z^{\prime }$ with a mass at most below the sub-GeV scale and an interaction strength $g_{\alpha \beta }$ between the active neutrinos ${\nu }_{\alpha }$ and ${\nu }_{\beta }$. We confirm that these experiments have the capability to significantly enhance the current sensitivities on $g_{\alpha \beta }$ for $m_{Z^{\prime }}\lesssim 500\mathrm{MeV}$ due to the production of high-energy neutrinos and excellent ability to detect tau neutrinos. Our analysis highlights the crucial role of “downward-going” DUNE atmospheric data in the search for secret neutrino interactions because of the rejection of backgrounds dominated in the upward-going events. Specifically, ten years of DUNE atmospheric data can provide the best sensitivities on $g_{e\tau }$ and $g_{\mu \tau }$ which are about 2 orders of magnitude improvement. In addition, the beam-based experiments such as FLArE100 and $\mathrm{FASER}\nu 2$ can improve the current constraint on $g_{e\tau }$ and $g_{\mu \tau }$ by more than an order of magnitude after the full running of the high luminosity LHC with the integrated luminosity of $3{\mathrm{ab}}^{-1}$. For $g_{e\mu }$ and $g_{ee}$ the SHiP experiment can play the most important role in the high-energy region of $m_{Z^{\prime }}>\mathrm{few}100\mathrm{MeV}$, and FLArE100 and $\mathrm{FASER}\nu 2$ can set the most stringent constraints for $m_{Z^{\prime }}$ less than few keV, in particular, if atmospheric flux uncertainty reduces DUNE sensitivity. Although our analysis is proceeded under our reference scenario of secret $Z^{\prime }$, our analysis strategies can be readily applicable to other types of secret interactions such as Majoron models.

Results obtained with stochastic methods have an inherent uncertainty due to the finite number of samples that can be achieved in practice. In lattice QCD this problem is particularly salient in some observables like, for instance, observables involving one or more baryons and it is the main problem preventing the calculation of nuclear forces from first principles. The method of control variables has been used extensively in statistics and it amounts to computing the expectation value of the difference between the observable of interest and another observable whose average is known to be zero but is correlated with the observable of interest. Recently, control variates methods emerged as a promising solution in the context of lattice field theories. In our current study, instead of relying on an educated guess to determine the control variate, we utilize a neural network to parametrize this function. Using $1+1$ dimensional scalar field theory as a testbed, we demonstrate that this neural network approach yields substantial improvements. Notably, our findings indicate that the neural network ansatz is particularly effective in the strong coupling regime.

Building on recent advances in studying the cohomological properties of Feynman integrals, we apply intersection theory to the computation of Fourier integrals. We discuss applications pertinent to gravitational bremsstrahlung and deep inelastic scattering in the saturation regime. After identifying the bases of master integrals, the latter are evaluated by means of the differential equation method. Finally, new results with exact dependence on the spacetime dimension D are presented.

The weak radiative decay of $D^0\to V\gamma$ with $V={\overline{K}}^0$, and $\varphi$, ${\rho }^0$, and $\omega$, is systematically studied in the vector meson dominance model. It allows us to distinguish the short-distance mechanisms which can be described by the tree-level transitions in the nonrelativistic constituent quark model, and the long-distance mechanisms which are related to the final-state interactions (FSIs). We find that the FSI effects play a crucial role in $D^0\to V\gamma$ and the SU(3) flavor symmetry can provide a natural constraint on the relative phase between the short and long-distance transition amplitudes. Our analysis suggests that the $D$-meson weak radiative decays can serve as a good case for investigating the nonperturbative QCD mechanisms at the charm quark mass region.

We introduce a novel approach for deriving one-loop Bern-Carrasco-Johansson (BCJ) numerators and reveal the world-sheet origin of the one-loop double copy. Our work shows that expanding Cachazo-He-Yuan half-integrands into generalized Parke-Taylor factors intrinsically generates BCJ numerators on quadratic propagators satisfying Jacobi identities. We validate our methodology by successfully reproducing one-loop BCJ numerators for the nonlinear sigma model as well as those of pure Yang-Mills theory in four dimensions with all-plus or single-minus helicities.

Understanding the interface dynamics in nonequilibrium quantum systems remains a challenge. We study the interface dynamics of strongly coupled immiscible binary superfluids by using holographic duality. The full nonlinear evolution of the binary superfluids with a relative velocity shows rich nonlinear patterns toward quantum turbulence, which is reminiscent of the quantum Kelvin-Helmholtz instability. The wave number of the fastest growing modes $k_0$ extracted from the interface pattern yields a nonmonotonic dependence of the relative velocity, independent of the temperature and interaction. The value of $k_0$ first increases with the velocity difference and then decreases, which stands in sharp contrast to the results of mean-field theory described by the Gross-Pitaevskii equation and is confirmed by using the linear analyses on top of the stationary configuration. We uncover that the critical velocity associated with the maximum corresponds to the case when the mean separation of vortices generated by interface instabilities becomes comparable to the vortex size, which could be a universal physical mechanism at strongly interacting superfluids and is directly testable in laboratory experiments.

In this work we analyze the possibility of sudden cosmological singularities, also known as type-II singularities, in the background of a Friedmann-Lemaître-Robertson-Walker geometry in an extension of general relativity known as Aether scalar-tensor theories (AeST). Similarly to several scalar-tensor theories, we observe that sudden singularities may occur in certain AeST models at the level of the second-order time derivative of the scale factor. These singularities can either be induced by AeST’s scalar field itself in the absence of a fluid matter component, or by a divergence of the pressure component of the fluid. In the latter case, one observes that the second-order time derivative of the scalar field $Q$ is also divergent at the instant the sudden singularity happens. We show that the sudden singularities can be prevented by an appropriate choice of the action and initial conditions, for which a divergence in the scalar field compensates the divergence in the pressure component of the matter fluid, thus preserving the regularity of the scale factor and all its time derivatives. For the models featuring a sudden singularity in the second-order time derivative of the scale factor, an analysis of the cosmographic parameters, namely the Hubble and the deceleration parameters, indicates that cosmological models featuring sudden singularities are allowed by the current cosmological measurements. Furthermore, an analysis of the jerk parameter favors cosmological models that attain a sudden singularity at a faster rate, up to a time of at most $t_s\sim 1.2t_0$, where $t_0$ is the current age of the Universe, and with negative values for the cosmological snap parameter.

We use the numerical continued fraction method to investigate the quasinormal mode spectra of extremal and nonextremal Reissner-Nordström black holes in the low- and intermediate-damping regions. In the extremal case, we develop techniques that significantly expand the calculated spectrum from what had previously appeared in the literature. This allows us to determine the asymptotic behavior of the extremal spectrum in the high-damping limit, where there are conflicting published results. Our investigation further supports the idea that the extremal limit of the nonextremal case, where the charge approaches the mass of the black hole in natural units, leads to the same vibrational spectrum as in the extremal case despite the qualitative differences in their topology. In addition, we numerically explore the quasinormal mode spectrum for a Reissner-Nordström black hole in the small-charge limit.

We analyze the stability of the vector and axial sectors of Poincaré gauge theory around general backgrounds in the presence of cubic-order invariants defined from the curvature and torsion tensors, showing how the latter can in fact cancel out well-known instabilities arising from the quadratic curvature invariants of the theory and accordingly help in the construction of healthy models with both curvature and torsion. For this task, we introduce the most general parity-preserving cubic Lagrangian with mixing terms of the curvature and torsion tensors, and find the relations of its coefficients to avoid a pathological behavior from the vector and axial modes of torsion. As a result, on top of the gravitational constant of general relativity and the mass parameters of torsion, our action contains 23 additional coupling constants controlling the dynamics of this field. As in the quadratic Poincaré gauge theory, we show that a further restriction on the cubic part of the action allows the existence of Reissner-Nordström-like black hole solutions with dynamical torsion.

Primordial black holes can be formed from the collapse of large-amplitude perturbation on small scales in the early Universe. Such an enhanced spectrum can be realized by introducing a flat region in the potential of single-field inflation, which makes the inflaton go into a temporary ultraslow-roll period. In this paper, we calculate the bispectrum of curvature perturbation in such a scenario. We explicitly confirm that bispectrum satisfies Maldacena’s theorem. At the end of the ultraslow-roll period, the bispectrum is generated by bulk interaction and field redefinition. At the end of inflation, bispectrum is generated only by bulk interaction. We also calculate the one-loop correction to the power spectrum from the bispectrum, called the source method. We find it consistent with the calculation of the one-loop correction from the second-order expansion of in-in perturbation theory.

In the present work, we derive a linearly stable and causal theory of relativistic third-order viscous hydrodynamics from the Boltzmann equation with relaxation-time approximation. We employ viscous correction to the distribution function obtained using a Chapman-Enskog like iterative solution of the Boltzmann equation. Our derivation highlights the necessity of incorporating a new dynamical degree of freedom, specifically an irreducible tensor of rank three, within this framework. This differs from the recent formulation of causal third-order theory from the method of moments which requires two dynamical degrees of freedom: an irreducible third-rank and a fourth-rank tensor. We verify the linear stability and causality of the proposed formulation by examining perturbations around a global equilibrium state.

We present the first direct ab initio computation of unequal-time correlation functions in non-Abelian lattice gauge theory. We demonstrate nontrivial consistency relations among correlators, time-translation invariance, and agreement with Monte Carlo results for thermal equilibrium in $3+1$ dimensions by employing our stabilized complex Langevin method. Our work sets the stage to extract real-time observables, relevant to quark-gluon plasma physics within a first-principles real-time framework.