The seesaw extension of the SM explains the tiny neutrino masses, and it is accompanied by many $CP$ violating phases. We study the case where all leptonic $CP$ violation arises from the soft breaking in the heavy Majorana mass matrix. Parameter counting reveals that one less parameter is needed to describe this case. This reduction leads to restrictions on the parameter space of heavy neutrinos. We analyze the minimal seesaw case in detail and find that mass degeneracy of heavy neutrinos is not possible for certain values of the $CP$ phases.

The muonium-to-antimuonium transition experiment is about to be updated. Notably, the experiment at Japan Proton Accelerator Research Complex (J-PARC) can explore the magnetic field dependence of the transition probability. In this paper, we investigate the information that we can extract from the transition probabilities across different magnetic field strengths, while also taking into account a planned transition experiment at China Spallation Neutron Source (CSNS). There are two model-independent parameters in the transition amplitude, and we ascertain the feasibility of determining these parameters, including their relative physical phase, from experimental measurements. This physical phase can be related to the electron electric dipole moment, which is severely constrained by experiments. The underlying mediator responsible for the transition can be either doubly charged particles or neutral particles. In the former case, typical magnetic fields yield specific probability ratios, while the latter presents a range of the probability ratio. We investigate several models with neutral mediators and elucidate that the probability ratio is linked to the sign of new physics contribution to the electron $g-2$. The pivotal role of the J-PARC transition experiment in shedding light on these insights is emphasized.

We studied integration contour deformations in the chiral random matrix theory of Stephanov [Phys. Rev. Lett. 76, 4472 (1996)] with the goal of alleviating the finite-density sign problem. We considered simple ansätze for the deformed integration contours and optimized their parameters. We find that optimization of a single parameter manages to considerably improve on the severity of the sign problem. We show numerical evidence that the improvement achieved is exponential in the degrees of freedom of the system, i.e., the size of the random matrix. We also compare the optimization method with contour deformations coming from the holomorphic flow equations.

We present the first fully differential predictions for tau neutrino scattering in the energy region relevant to the DUNE experiment, including all spin correlations and all tau lepton decay channels. The calculation is performed using a generic interface between the neutrino event generator achilles and the publicly available, general-purpose collider event simulation framework sherpa.

We use unlabeled collision data and weakly supervised learning to train models that can distinguish prompt muons from nonprompt muons using patterns of low-level particle activity in the vicinity of the muon and interpret the models in the space of energy flow polynomials. Particle activity associated with muons is a valuable tool for identifying prompt muons, those due to heavy boson decay, from muons produced in the decay of heavy flavor jets. The high-dimensional information is typically reduced to a single scalar quantity, isolation, but previous work in simulated samples suggests that valuable discriminating information is lost in this reduction. We extend these studies in LHC collisions recorded by the CMS experiment, where true class labels are not available, requiring the use of the invariant mass spectrum to obtain macroscopic sample information. This allows us to employ classification without labels, a weakly supervised learning technique, to train models. Our results confirm that isolation does not describe events as well as the full low-level calorimeter information, and we are able to identify single energy flow polynomials capable of closing the performance gap. These polynomials are not the same ones derived from simulation, highlighting the importance of training directly on data.

We revisit the Bose-Marletto-Vedral (BMV) tabletop experimental proposal—which aims to witness quantum gravity using gravity-mediated entanglement—analyzing the role of locality in the experiment. We first carry out a fully quantum modeling of the interaction of matter and gravity and then show in what way gravity-mediated entanglement in the BMV experiment could be accounted for without appealing to quantum degrees of freedom of the gravitational field. We discuss what assumptions are needed in order to interpret the current BMV experiment proposals as a proof of quantum gravity, and also identify the modifications that a BMV-like experiment could have in order to serve as proof of quantum gravity without having to assume the existence of local mediators in the gravitational field.

Recent advances in machine learning establish the ability of certain neural-network architectures called neural operators to approximate maps between function spaces. Motivated by a prospect of employing them in fundamental physics, we examine applications to scattering processes in quantum mechanics. We use an iterated variant of Fourier neural operators to learn the physics of Schrödinger operators, which map from the space of initial wave functions and potentials to the final wave functions. These deep operator learning ideas are put to test in two concrete out-of-distribution problems: a neural operator predicting the time evolution of a wave packet scattering off a central potential in $1+1$ dimensions, and the double-slit experiment in $2+1$ dimensions. At inference, neural operators can become orders of magnitude more efficient compared to traditional finite-difference solvers.

$\mathrm{AdS}/\mathrm{CFT}$ correspondence is a “first-principle” tool to study the strongly coupled many-body systems. While it has been extensively applied to investigate the continuous symmetry breaking dynamics, the dynamics of discrete symmetry breaking are rarely investigated. In this paper, the model of kink formation in a strongly coupled one-dimensional chain is realized from the $\mathrm{AdS}/\mathrm{CFT}$ correspondence. In doing so, we first construct a model of real scalar fields with parity symmetries in the AdS bulk. By quenching the system across the critical point at a finite rate, kink hairs turn out in the bulk due to the spontaneous parity symmetry breaking, which accomplishes a counterexample of “no hair conjecture” of black hole. Due to the $\mathrm{AdS}/\mathrm{CFT}$ correspondence, kink hairs in the bulk are dual to the kinks in the AdS boundary. The mean of the dual kink numbers are found to satisfy a universal power-law relation to the quench rate, in agreement with the celebrated Kibble-Zurek mechanism. Moreover, the higher cumulants of the kink numbers are proportional to the mean numbers, consistent with the assumption that the formation of kinks satisfy the binomial distributions which goes beyond the Kibble-Zurek mechanism.

No experimental evidence of the quantum nature of gravity has been observed yet and a realistic setup with improved sensitivity is eagerly awaited. We find two effects, which can substantially enhance the signal of gravity-induced quantum entanglement, by examining an optomechanical system in which two oscillators gravitationally couple and one composes an optical cavity. The first effect comes from a higher-order term of the optomechanical interaction and generates the signal at the first order of the gravitational coupling in contrast to the second-order results in previous works. The second effect is the resonance between the two oscillators. If their frequencies are close enough, the weak gravitational coupling effectively strengthens. Combining these two effects, the signal in the interference visibility could be amplified by a factor of ${10}^{24}$ for our optimistic parameters. The two effects would be useful in seeking feasible experimental setups to probe quantum gravity signals.

A longstanding problem with the popular Sakai-Sugimoto holographic dual of thermal QCD is that the mesinos, the (nonsupersymmetric) fermionic partners of the mesons, are nearly isospectral with mesons and have an unsuppressed mesino-mesino-meson interaction, both being in contradiction with actual QCD. We solve this problem in a UV complete (and different) type-IIA string dual at intermediate coupling of realistic thermal QCD, in which the mesinos are shown to be much heavier than and noninteracting with mesons (the wave function/mass/interaction terms receiving no $\mathcal{M}$-theory $\mathcal{O}(R^4)$ corrections). In particular we derive a large-$N$ enhancement of the Kaluza-Klein $(KK)$ mass scale $M_{KK}$ (from $M_{KK}$ to $M_{KK}^{\mathrm{eff}}\sim N^{1+\frac{1}{\mathcal{O}(1)}}{M}_{KK}$) arising from the construction of the type-IIA mirror [1] of the type-IIB dual [2] of thermal QCD-like theories, as well as the generation of a one-parameter family of $M_{KK}$-independent mass scale at $\mathcal{O}(R^4)$ in the $\mathcal{M}$-theory uplift [3], wherein the parameter can be made appropriately large. We also show that the mesino-mesino-single-($\rho /\pi$)meson interactions, vanish identically in the aforementioned type-IIA holographic dual.

Entanglement temperatures (ET) are a generalization of Unruh temperatures valid for states reduced to any region of space. They encode in a thermal fashion the high-energy behavior of the state around a point. These temperatures are determined by an eikonal equation in Euclidean space. We show that the real-time continuation of these equations implies ballistic propagation. For theories with a free UV fixed point, the ET determines the state at a large modular temperature. In particular, we show that the $n\to 0$ limit of Rényi entropies $S_n$ can be computed from the ET. This establishes a formula for these Rényi entropies for any region in terms of solutions of the eikonal equations. In the $n\to 0$ limit, the relevant high-temperature state propagation is determined by a free relativistic Boltzmann equation, with an infinite tower of conserved currents. For the special case of states and regions with a conformal Killing symmetry, these equations coincide with the ones of a perfect fluid.

We develop a consistent approach to calculate the moment of inertia (MOI) for axisymmetric neutron stars (NSs) in the Lorentz-violating Standard-Model Extension (SME) framework. To our knowledge, this is the first relativistic MOI calculation for axisymmetric NSs in a Lorentz-violating gravity theory other than deformed, rotating NSs in general relativity. Under Lorentz violation, there is a specific direction in the spacetime, and NSs get stretched or compressed along that direction. When a NS is spinning stationarily along this direction, a conserved angular momentum and the concept of MOI are well defined. In the SME framework, we calculate the partial differential equation governing the rotation and solve it numerically with the finite element method to get the MOI for axisymmetric NSs caused by Lorentz violation. Besides, we study an approximate case where the correction to the MOI is regarded solely from the deformation of the NS and compare it with its counterpart in the Newtonian gravity. Our formalism and the numerical method can be extended to other theories of gravity for static axisymmetric NSs.

In some modified theories of gravity, gravitational waves can contain up to six different polarizations, which can travel at speeds different from that of light. Searches for these different polarizations in gravitational wave data are important because any detection would be clear evidence of new physics, while clear nondetections could constrain some modified theories. The first step toward searching the data for such gravitational wave content is the calculation of the amplitudes of these different polarizations. Here we present a model-independent method to obtain the different polarizations of gravitational waves directly from the metric perturbation in theories where these polarizations are allowed to travel at different speeds. We develop our calculations so that the same procedure works with either the metric perturbation itself or its trace-reversed form. Our results are in agreement with previous work in the limit that all polarization speeds are the speed of light. We demonstrate how our model-independent method can be used with two specific modified theories of gravity, suggesting its wide applicability to other theories that allow for different gravitational wave propagation speeds. We further extend the parametrized post-Einsteinian formalism to apply to such theories that travel with different speeds. Finally, we discuss how the different speeds of different polarizations may affect null stream tests of general relativity with gravitational wave observations by multiple interferometers. Differences in propagation speeds may make null streams ineffective or lead to the detection of what seem to be isolated scalar or vector modes.

The Friedmann equation, augmented with an additional term that effectively takes on the role of dark energy, is demonstrated to be an exact solution to the recently proposed gravitational theory named “conformal Killing gravity.” This theory does not explicitly incorporate dark energy. This finding suggests that there is no necessity to postulate the existence of dark energy as an independent physical entity. The dark energy derived from this theory is characterized by a specific equation of state parameter, denoted as $\omega$, which is uniquely determined to be $-5/3$. If this effective dark energy is present, typically around 5% of the total energy density at the present time, and under the assumption of density parameters for matter and the cosmological constant, ${\mathrm{\Omega }}_{\mathrm{m}}\sim 0.25$ and ${\mathrm{\Omega }}_{\mathrm{\Lambda }}\sim 0.7$, respectively, the expansion of the universe at low redshifts ($z<1.5$) can exceed expectations, while the expansion at $z>1.5$ remains unchanged. This offers a potential solution to the Hubble tension problem. Alternatively, effective dark energy could be a dominant component in the present-day universe. In this scenario, there is also the potential to address the Hubble tension, and furthermore, it resolves the coincidence problem associated with the cosmological constant.

It has been shown that both scalar and tensor modes with non-Bunch-Davies initial states can enhance the amplitudes of the primordial bispectra compared to those with the Bunch-Davies state, especially for wave number modes in a flattened triangle configuration. However, in the case of the non-Bunch-Davies scalar modes, it has also been found that those enhancements in Fourier space are somewhat reduced in bispectra of cosmic microwave background (CMB) fluctuations. In this paper, we show that the enhancement resulting from the tensor modes is partially reduced to a degree differing from that of the scalar modes, which makes the non-Bunch-Davies effects unobservable in gravitational theories with the same quadratic and cubic operators of the tensor perturbations as general relativity. Furthermore, we present examples of gravitational theories yielding enhancements that would potentially be detected through CMB experiments.

Doppler anisotropies, induced by our relative motion with respect to the source rest frame, are a guaranteed property of stochastic gravitational wave backgrounds of cosmological origin. If detected by future pulsar timing array measurements, they will provide interesting information on the physics sourcing gravitational waves, which is hard or even impossible to extract from measurements of the isotropic part of the background only. We analytically determine the pulsar response function to kinematic anisotropies, including possible effects due to parity violation, to features in the frequency dependence of the isotropic part of the spectrum, as well as to the presence of extra scalar and vector polarizations. For the first time, we show how the sensitivity to different effects crucially depends on the pulsar configuration with respect to the relative motion among frames. Correspondingly, we propose examples of strategies of detection, each aimed at exploiting future measurements of kinematic anisotropies for characterizing distinct features of the cosmological gravitational wave background.

Strongly lensed gravitational waves (GWs) from binary coalescence manifest as repeated chirps from the original merger. At the detectors, the phase of the lensed GWs and its arrival time differences will be consistent modulo a fixed constant phase shift. We develop a fast and reliable method to efficiently reject event pairs that are not-lensed copies and appropriately rank the most interesting candidates. Our method exploits that detector phases are the best measured GW parameter, with errors only of a fraction of a radian and differences across the frequency band that are better measured than the chirp mass. The arrival time phase differences also avoid the shortcomings of looking for overlaps in highly non-Gaussian sky maps. Our basic statistic determining the consistency with lensing is the distance between the phase posteriors of two events and it directly provides information about the lens-source geometry which helps inform electromagnetic follow-ups. We demonstrate that for simulated signals of not-lensed binaries specifically chosen with many coincident properties so as to trigger false lensing alarms none of the pairs have phases closer than $3\sigma$, and most cases reject the lensing hypothesis by $5\sigma$. Looking at the latest catalog, GWTC3, we find that only 6% of the pairs are consistent with lensing at 99% confidence level. Moreover, we reject about half of the pairs that would otherwise favor lensing by their parameter overlaps and demonstrate good correlation with detailed joint parameter estimation results. This reduction of the false alarm rate will be of paramount importance in the upcoming observing runs and the eventual discovery of lensed GWs. Our code is publicly available and could be applied beyond lensing to test possible deviations in the phase evolution from modified theories of gravity and constrain GW birefringence.

TianQin (TQ) project plans to deploy three satellites in space around the Earth to measure the displacement change of test masses caused by gravitational waves via laser interferometry. The requirement of the acceleration noise of the test mass is on the order of ${10}^{-15}\mathrm{m}{\mathrm{s}}^{-2}{\mathrm{Hz}}^{-1/2}$ in the sensitive frequency range of TQ, which is so stringent that the acceleration noise caused by the interaction of the space magnetic field with the test mass needs to be investigated. In this work, by using the Tsyganenko model, a data-based empirical space magnetic field model, we obtain the magnetic field distribution around TQ’s orbit spanning two solar cycles in 23 years from 1998 to 2020. With the obtained space magnetic field, we derive the distribution and amplitude spectral densities of the acceleration noise of TQ in 23 years. Our results reveal that the average values of the ratio of the acceleration noise caused by the space magnetic field to the requirements of TQ at 1 mHz ($R_{1\mathrm{mHz}}$) and 6 mHz ($R_{6\mathrm{mHz}}$) are $0.123\pm 0.052$ and $0.027\pm 0.013$, respectively. The occurrence probabilities of $R_{1\mathrm{mHz}}>0.2$ and $>0.3$ are only 7.9% and 1.2%, respectively, and $R_{6\mathrm{mHz}}$ never exceeds 0.2.

The interconversion of axionlike particles (ALPs) and photons in magnetized astrophysical environments provides a promising route to search for ALPs. The strongest limits to date on light ALPs use galaxy clusters as ALP-photon converters. However, such studies traditionally rely on simple models of the cluster magnetic fields, with the state-of-the-art being Gaussian random fields (GRFs). We present the first systematic study of ALP-photon conversion in more realistic, turbulent fields from dedicated magnetohydrodynamic (MHD) simulations, which we compare with GRF models. For GRFs, we analytically derive the distribution of conversion ratios at fixed energy and find that it follows an exponential law. We find that the MHD models agree with the exponential law for typical, small-amplitude mixings but exhibit distinctly heavy tails for rare and large mixings. We explain how non-Gaussian features, e.g., coherent structures and local spikes in the MHD magnetic field, are responsible for the heavy tail. Our results suggest that limits placed on ALPs using GRFs are robust.

The study of strange quark matter within the framework of the density-dependent MIT bag model using the grand canonical ensemble is thermodynamically inconsistent. In this work, it is shown that if the medium effects are incorporated through a density-dependent bag pressure in the grand canonical ensemble, then the Euler relation is violated. If Euler relation is used then the minimum of energy per baryon does not occur at zero pressure. In order to overcome this inconsistency, we propose the medium effect of the strange quark matter in the form of chemical potential dependent bag pressure in the grand canonical ensemble. The density dependent bag pressure which has been used in the grand canonical ensemble so far can, however, be used in the canonical ensemble without violating the laws of thermodynamics. These prescriptions will obey the Euler relation as well as the minimum energy per baryon will coincide with the zero of pressure and hence can be considered to be self-consistent. These equations of state in the grand canonical ensemble can be further used to construct the mass-radius and other structural properties of the strange quark stars as well as hybrid stars. In our present work we have calculated the mass radius diagram of strange stars only using this formalism.