We construct the standard and dual supertranslation charges on the future horizon of the Schwarzschild black hole, using the first-order formulation of gravity with the Holst action. The Dirac bracket algebra of standard and dual supertranslation charges is shown to exhibit a central term in the presence of singularities in the two-sphere function associated with supertranslation. We show that one can cancel this anomalous term and restore the asymptotic symmetry algebra by introducing a gravitational Chern-Simons theory on the horizon. This demonstrates that consistency of the asymptotic symmetry algebra requires a new structure on the horizon.

In this paper, we analyze the quantum vacuum in a radiation-dominated and $CPT$-invariant universe by further imposing the quantum states to be ultraviolet regular i.e., satisfying the Hadamard/adiabatic condition. For scalar fields, this is enforced by constructing the vacuum via the states of low-energy proposal. For spin-$\frac{1}{2}$ fields, we extend this proposal for a FLRW spacetime and apply it for the radiation-dominated and $CPT$-invariant universe. We focus on minimizing the smeared energy density around the big bang and give strong evidence that the resulting states satisfy the Hadamard/adiabatic condition. These states are then self-consistent candidates as effective big bang quantum vacuum from the field theory perspective.

Deep learning techniques for gravitational-wave parameter estimation have emerged as a fast alternative to standard samplers—producing results of comparable accuracy. These approaches (e.g., DINGO) enable amortized inference by training a normalizing flow to represent the Bayesian posterior conditional on observed data. By conditioning also on the noise power spectral density (PSD) they can even account for changing detector characteristics. However, training such networks requires knowing in advance the distribution of PSDs expected to be observed and therefore can only take place once all data to be analyzed have been gathered. Here, we develop a probabilistic model to forecast future PSDs, greatly increasing the temporal scope of trained deep learning models. Using PSDs from the second LIGO-Virgo observing run (O2)—plus just a single PSD from the beginning of the third (O3)—we show that we can train a DINGO network to perform accurate inference throughout O3 (on 37 real events). We therefore expect this approach to be a key component to enable the use of deep learning techniques for low-latency analyses of gravitational waves.

An isotropic stochastic background of nanohertz gravitational waves creates excess residual power in pulsar-timing-array datasets, with characteristic interpulsar correlations described by the Hellings-Downs function. These correlations appear as nondiagonal terms in the noise covariance matrix, which must be inverted to obtain the pulsar-timing-array likelihood. Searches for the stochastic background, which require many likelihood evaluations, are therefore quite computationally expensive. We propose a more efficient method: we first compute approximate posteriors by ignoring cross correlations and then reweight them to exact posteriors via importance sampling. We show that this technique results in accurate posteriors and marginal likelihood ratios, because the approximate and exact posteriors are similar, which makes reweighting especially accurate. The Bayes ratio between the marginal likelihoods of the exact and approximate models, commonly used as a detection statistic, is also estimated reliably by our method, up to ratios of at least ${10}^6$.

In plane wave spacetimes, we find that there will be a precession angle deviation between two free-falling gyroscopes when gravitational waves passed through. This kind of angle deviation is closely related to the well-known standard velocity memory effect. Initial conditions such as the separation velocity or displacement between the two gyroscopes will affect this angle deviation. This result might be understood as a special relativistic consequence of the velocity memory. The evolutions of the angle deviation are calculated for different cases. We find that in some extreme circumstances, the angle deviation’s order of magnitude produced by a rotating compact binary source could be ${10}^{-14}\mathrm{rads}$. Therefore, this memory effect caused by the gravitational wave is likely to be detected in the future.

In this paper, we use the publicly available observational data of 17 stellar stars orbiting Sgr A* to test the quantum extension of Schwarzschild spacetime in loop quantum gravity (LQG). For our purpose, we transform the geodesical evolution of a massive particle in the quantum-extended Schwarzschild black hole to the perturbed Kepler problem and calculate the effects of LQG on the pericenter advance of the stellar stars. With these effects, one is able to compare them with the publicly available astrometric and spectroscopic data of stellar stars in the galactic center. We perform Monte Carlo Markov Chain (MCMC) simulations to probe the possible LQG effects on the orbit of S-stars. No significant evidence of the quantum-extended Schwarzschild black hole from LQG is found. Among the posterior analyses of 17 S-stars, the result of S2 gives the strongest bound on the LQG parameter $A_{\lambda }$, which places an upper bound at 95% confidence level on $A_{\lambda }$ to be $A_{\lambda }<0.302$.

We investigate the collision-induced flavor instability in homogeneous, isotropic, dense neutrino gases in the two-flavor mixing scenario with energy-dependent scattering. We uncover a simple expression of the growth rate of this instability in terms of the flavor-decohering collision rates and the electron lepton number distribution of the neutrino. This growth rate is common to the neutrinos and antineutrinos of different energies, and is independent of the mass splitting and vacuum-mixing angle of the neutrino, the matter density, and the neutrino density, although the initial amplitude of the unstable oscillation mode can be suppressed by a large matter density. Our results suggest that neutrinos are likely to experience collision-induced flavor conversions deep inside a core-collapse supernova even when both the fast and slow collective flavor oscillations are suppressed.

The method of time-delay interferometry (TDI) is proposed to cancel the laser noise in space-borne gravitational-wave detectors. Among all different TDI combinations, the most commonly used ones are the orthogonal channels A, E, and T, where A and E are signal-sensitive and T is signal-insensitive. Meanwhile, for the detection of stochastic gravitational-wave background, one needs to introduce the overlap reduction function to characterize the correlation between channels. For the calculation of overlap reduction function, it is often convenient to work in the low-frequency approximation, and assuming the equal-arm Michelson channels. However, if one wishes to work on the overlap reduction function of $\mathrm{A}/\mathrm{E}$ channels, then the low-frequency approximation fails. We derive the exact form of overlap reduction function for $\mathrm{A}/\mathrm{E}$ channels. Based on the overlap reduction function, we calculate the sensitivity curves of TianQin, TianQin $\mathrm{I}+\mathrm{II}$, and $\mathrm{TianQin}+\text{LISA}$. We conclude that the detection sensitivity calculated with $\mathrm{A}/\mathrm{E}$ channels is mostly consistent with that obtained from the equal-arm Michelson channels.

Some extensions of the Standard Model of particle physics allow for Lorentz invariance and charge-parity-time invariance violations. In the neutrino sector strong constraints have been set by neutrino-oscillation and time-of-flight experiments. However, some Lorentz-invariance-violating parameters are not accessible via these probes. In this work, we focus on the parameters $(a_{\mathrm{of}}^{(3)}{)}_{00}$, $(a_{\mathrm{of}}^{(3)}{)}_{10}$, and $(a_{\mathrm{of}}^{(3)}{)}_{11}$ which would manifest themselves in a nonisotropic $\beta$-decaying source as a sidereal oscillation and an overall shift of the spectral endpoint. Based on the data of the first scientific run of the KATRIN experiment, we set the first 90% confidence-level limit on $|(a_{\mathrm{of}}^{(3)}{)}_{11}|$ of $<0.9\times {10}^{-6}\mathrm{GeV}$ to $3.7\times {10}^{-6}\mathrm{GeV}$, depending on the phase. Moreover, we derive new constraints on $(a_{\mathrm{of}}^{(3)}{)}_{00}$ and $(a_{\mathrm{of}}^{(3)}{)}_{10}$.

Following neutron capture in a material, there will be prompt nuclear recoils in addition to the gamma cascade. The nuclear recoils that are left behind in materials are generally below 1 keV and therefore in the range of interest for dark matter experiments and $\mathrm{CE}\nu \mathrm{NS}$ studies—both as backgrounds and calibration opportunities. Here we obtain the spectrum of prompt nuclear recoils following neutron capture for silicon.

We investigate the interaction of strong color fields in the glasma stage of high-energy nuclear collisions with the spins of quarks and antiquarks. We employ the perturbative solution of the quantum kinetic theory for the spin transport of (massive) quarks in a background color field governed by the linearized Yang-Mills equation and derive expressions for the quark-spin polarization and quark-antiquark spin correlation at small momentum in terms of field correlators. For the Golec-Biernat–Wusthoff dipole distribution the quark-spin polarization vanishes, but the out-of-plane spin correlation of quarks and antiquarks is nonzero. Our order-of-magnitude estimate of the correlation far exceeds that caused by vorticity effects, but does not fully explain the data for vector meson alignment. We identify possible mechanisms that could further increase the predicted spin correlation.

The Gildener-Weinberg two-Higgs doublet model provides a naturally light and aligned Higgs boson, $H=H(125)$. It has been studied in the one-loop approximation of its effective potential, $V_1$. An important consequence is that the masses of the model’s beyond the Standard Model (BSM) Higgs bosons ($H^{\prime },A,H^{\pm }$) are bounded by the sum rule ${(M_{H^{\prime }}^4+M_A^4+2M_{H^{\pm }}^4)}^{1/4}=540\mathrm{GeV}$. Although they are well within reach of the LHC, searches for them have been stymied by large QCD backgrounds. Another consequence is that $H$ is highly aligned, i.e., $H–H^{\prime }$ mixing is small and $H$ has only Standard Model couplings. A corollary of this alignment is that commonly pursued discovery modes such as $H^{\prime }$, $A\leftrightarrow W^{+}{W}^{-}$, $ZZ$, $HZ$, and $H^{\pm }\leftrightarrow W^{\pm }Z,W^{\pm }H$ are beyond the reach of LHC experiments. To assess the accuracy of the sum rule and Higgs alignment, we study this model in two loops. This calculation is complicated by having many new contributions. We present two formulations of it to calculate the $H–H^{\prime }$ mass matrix, its eigenvectors $H_1$, $H_2$, and the mass $M_{H_2}$ while fixing $M_{H_1}=125\mathrm{GeV}$. They give similar results and are in accord with the one-loop results. Requiring $M_A=M_{H^{\pm }}$, we find $180\mathrm{GeV}\lesssim M_{A,H^{\pm }}\lesssim 380–425\mathrm{GeV}$ and $550–700\mathrm{GeV}\gtrsim M_{H_2}\gtrsim 125\mathrm{GeV}$, with $M_{H_2}$ decreasing as $M_{A,H^{\pm }}$ increase. The corrections to $H$ alignment are below $\mathcal{O}(1\%)$. So, the BSM searches above will remain fruitless. Finding the BSM Higgses requires improved sensitivity to their low masses. We discuss three possible searches for this.

We discuss a left-right (L-R) symmetric model with the double seesaw mechanism at the TeV scale generating Majorana masses for the active left-handed (LH) flavor neutrinos ${\nu }_{\alpha L}$ and the heavy right-handed (RH) neutrinos $N_{\beta R},\alpha ,\beta =e,\mu ,\tau$, which in turn mediate lepton number violating processes, including neutrinoless double beta decay. The Higgs sector is composed of two Higgs doublets $H_L$, $H_R$, and a bidoublet $\mathrm{\Phi }$. The fermion sector has the usual for the L-R symmetric models quarks and leptons, along with three $SU(2)$ singlet fermion $S_{\gamma L}$. The choice of bare Majorana mass term for these sterile fermions induces large Majorana masses for the heavy RH neutrinos leading to two sets of heavy Majorana particles $N_j$ and $S_k,j,k=1,2,3$, with masses $m_{N_j}\ll m_{S_k}$. Working with a specific version of the model in which the ${\nu }_{\alpha L}-N_{\beta R}$ and the $N_{\beta R}-S_{\gamma L}$ Dirac mass terms are diagonal, and assuming that $m_{N_j}\sim (1–1000)\mathrm{GeV}$ and $\max (m_{S_k})\sim (1–10)\mathrm{TeV}$, $m_{N_j}\ll m_{S_k}$, we study in detail the new “nonstandard” contributions to the $0\nu \beta \beta$ decay amplitude and half-life arising due to the exchange of virtual $N_j$ and $S_k$. We find that in both cases of NO and IO light neutrino mass spectra, these contributions are strongly enhanced and are dominant at relatively small values of the lightest neutrino mass $m_{1(3)}\sim ({10}^{-4}–{10}^{-2})\mathrm{eV}$ over the light Majorana neutrino exchange contribution. In large part of the parameter space, the predictions of the model for the $0\nu \beta \beta$ decay generalized effective Majorana mass and half-life are within the sensitivity range of the planned next generation of neutrinoless double beta decay experiments LEGEND-200 (LEGEND-1000), nEXO, KamlAND-Zen-II, CUPID, and NEXT-HD.

As the two phenomena nonstandard interaction (NSI) in neutrino propagation and Lorentz invariance violation (LIV) modify the Hamiltonian of neutrino oscillation in a similar fashion, it is very difficult to distinguish these two effects. The only difference between them lies in the fact that NSI depends on the matter density, whereas LIV is independent of the earth matter effect. Therefore for a fixed baseline experiment, where matter density is constant, the theories describing NSI and LIV are exactly equivalent. However, as the present and future bounds of the NSI and LIV parameters are not equivalent, one can distinguish these two scenarios in the long-baseline neutrino experiments depending on their statistics with respect to the present and future bounds of these parameters. In this paper, we attempt to differentiate between LIV and NSI in the context of DUNE and P2SO, as these two future experiments are believed to be sensitive to the strongest matter effect and will have very large statistics. Taking LIV in the data and NSI in theory, our results show that indeed it is possible to have good discrimination between LIV and NSI. The best separation between LIV and NSI at $3\sigma \mathrm{C}.\mathrm{L}.$ is achieved for the parameter $a_{\mu \mu }$ with P2SO. In this case, the value of the LIV parameter, for which separation is possible, lies within its future bound if one considers the value of NSI parameter to be constrained by the present experiments. Between DUNE and P2SO, the latter has better sensitivity for such discrimination.

In this work, we explore the proposed mechanism in which the gravitational $\theta$ anomaly generates neutrino masses. We highlight that the leading renormalizable interactions of the neutrino condensate forbid the possibility of generating hierarchical masses consistent with observation. This conclusion still holds when Standard Model loop corrections are accounted for. We show that higher-dimensional operators can alleviate this problem. The higher-dimensional operators could be generated from the gravitational anomaly itself, but there is no clear way to know without a deeper understanding of the low-energy description of this mechanism. Because of that, we explore the possibility of new particles generating neutrino mass splittings. We show that both new particles that alter the scalar potential of the condensate or new particles in loops for the neutrino self-energy can solve this problem.

We propose new searches for $n^{\prime }$, a dark baryon that can mix with the Standard Model neutron. We show that IsoDAR, a proposal to place an intense cyclotron near a large-volume neutrino detector deep underground, can look for $n\to n^{\prime }\to n$ transitions with much lower backgrounds than surface experiments. This opportune neutron-shining-through-a-wall search would be possible without any modifications to the primary goals of the experiment and would provide the strongest laboratory constraints on the $n-n^{\prime }$ mixing for a wide range of mass splitting. We also consider dark neutrons as dark matter and show that their nuclear absorption at deep-underground detectors such as SNO and Borexino places some of the strongest limits in parameter space. Finally, we describe other $n^{\prime }$ signatures, such as neutrons shining through walls at spallation sources, reactors, and the disappearance of ultracold neutrons.

Scalar-field dark matter models imply small oscillations of fundamental constants. These oscillations could result in observable variations of the magnetic field in a permanent magnet. We propose an experiment for detection of this type of dark matter through searches of oscillations of magnetic field of permanent magnets with a SQUID magnetometer or a low-noise radiofrequency amplifier. We show that this experiment may have comparable sensitivity to leading experiments searching for variations of fundamental constants in the range of frequencies from a few Hz to about 1 MHz. We also discuss applicability of the approach of variations of fundamental constants for accounting for the interaction with scalar dark matter.

We investigate blow-up manifolds of $T^2/{\mathbb{Z}}_N(N=2,3,4,6)$ orbifolds with magnetic flux. First, we construct the blow-up manifolds and zero-mode wave functions on them more precisely. In particular, through an appropriate singular gauge transformation, winding numbers of wave functions on $T^2/{\mathbb{Z}}_N$ can be replaced with localized curvature and localized flux at orbifold fixed points. In addition, since the blow-up manifolds have no singularities, we apply the Atiyah-Singer index theorem to them; the chiral zero-mode number is given by the total magnetic flux. It can be also applied for $T^2/{\mathbb{Z}}_N$ orbifolds through the blow-up process, and then we find that it is consistent with the zero-mode counting formula in M. Sakamoto et al. [Zero-mode counting formula and zeros in orbifold compactifications, Phys. Rev. D 102, 025008 (2020).]. Furthermore, the Atiyah-Singer index theorem shows that an additional degree of freedom of localized flux gives new chiral zero modes. We study their wave functions and then we find that they correspond to localized modes at the orbifold singular points. We also calculate their Yukawa couplings.

A multipole decomposition of a cross section is a useful tool to simplify the analysis of reactions due to their symmetry properties. By using a new approach to decompose antisymmetric tensor-type interactions within the multipole analysis, we introduce a general mathematical formalism for working with tensor couplings. This allows us to present a general tensor nuclear response, which is particularly useful for ongoing $\beta$-decay experiments looking for physics beyond the Standard Model (BSM), as well as other exotic particle scatterings off nuclei, e.g., in dark matter direct detection experiments. Using this method, BSM operators identify with the known Standard Model operators, eliminating the need for calculations of additional matrix elements. We present in detail BSM expressions useful for $\beta$-decay experiments and give an exemplary application for ${}^6\mathrm{He}$ $\beta$-decay, although the formalism is easily generalizable for calculating other exotic scattering reactions.

We examine contributions to single Higgs boson production processes via $Z^{\prime }$ and $W^{\prime }$ bosons in the $SU(3{)}_C\times SO(5{)}_W\times U(1{)}_X$ gauge-Higgs unification (GHU) model. In particular, we analyze the cross sections of three single Higgs boson production processes $e^{-}{e}^{+}\to Zh$, $e^{-}{e}^{+}\to \nu \overline{\nu }h$, and $e^{-}{e}^{+}\to e^{-}{e}^{+}h$ in the SM and the GHU model. For the Higgs strahlung process $e^{-}{e}^{+}\to Zh$, we show that for a parameter region satisfying the current experimental constraints, a maximum deviation from the SM is about up to 6% for the center-of-mass energy of the initial electron and positron $\sqrt{s}=250\mathrm{GeV}$ and that from the SM is about up to 20% for $\sqrt{s}=500\mathrm{GeV}$, depending on the initial polarization of electron and positron. The deviation from the SM is monotonically increasing with respect to $\sqrt{s}$ for $\sqrt{s}\lesssim 1\mathrm{TeV}$. By using the Higgs strahlung process, it is possible to explore up to the region of tens of TeV in terms of the Kaluza-Klein (KK) mass. We also show that the sign of the bulk mass of a lepton multiplet in the GHU model can be determined by examining the deviation of the left-right symmetry of the $e^{-}{e}^{+}\to Zh$ process from the SM. The contributions to the cross sections of the $e^{-}{e}^{+}\to \nu \overline{\nu }h$ and $e^{-}{e}^{+}\to e^{-}{e}^{+}h$ processes via the $Z^{\prime }$ and $W^{\prime }$ bosons are relatively small compared to that for $e^{-}{e}^{+}\to Zh$ at least for $\sqrt{s}\le 1\mathrm{TeV}$. As is the same as in the SM, the $e^{-}{e}^{+}\to \nu \overline{\nu }h$ process gives a main contribution to the single Higgs boson production processes for $\sqrt{s}\gtrsim 500\mathrm{GeV}$, but large deviations from the SM are only observed on energy scales close to the masses of the first KK gauge bosons or higher.