Generation of simulated data is essential for data analysis in particle physics, but current Monte Carlo methods are very computationally expensive. Deep-learning-based generative models have successfully generated simulated data at lower cost, but struggle when the data are very sparse. We introduce a novel deep sparse autoregressive model (SARM) that explicitly learns the sparseness of the data with a tractable likelihood, making it more stable and interpretable when compared to generative adversarial networks (GANs) and other methods. In two case studies, we compare SARM to a GAN model and a nonsparse autoregressive model. As a quantitative measure of performance, we compute the Wasserstein distance ($W_p$) between the distributions of physical quantities calculated on the generated images and on the training images. In the first study, featuring images of jets in which 90% of the pixels are zero valued, SARM produces images with $W_p$ scores that are 24%–52% better than the scores obtained with other state-of-the-art generative models. In the second study, on calorimeter images in the vicinity of muons where 98% of the pixels are zero valued, SARM produces images with $W_p$ scores that are 66%–68% better. Similar observations made with other metrics confirm the usefulness of SARM for sparse data in particle physics.

Measurements of cosmic neutrinos have a reach potential for providing an insight into fundamental neutrino properties. For this a precise knowledge about an astrophysical environment of cosmic neutrinos propagation is needed. However this is not always possible, and the lack of information can bring about theoretical uncertainties in our physical interpretation of the results of experiments on cosmic neutrino fluxes. We formulate an approach that allows one to quantify the uncertainties using the apparatus of quantum measurement theory. We consider high-energy Dirac neutrinos emitted by some distant source and propagating towards Earth in the interstellar space. We take into account the neutrino magnetic moment interaction with stochastic interstellar magnetic fields and describe the neutrino evolution in the formalism of the Lindblad master equation for the neutrino density matrix. It is supposed that neutrinos on their way to Earth pass through highly magnetized dense layers of a cosmic object that “stops” left-handed neutrinos and lets only sterile, right-handed neutrinos to propagate farther. Such a filter mimics the strongest effect on the neutrino flux that can be induced by the cosmic object and that can be missed in the theoretical interpretation of the lab measurements due to the insufficient information about the astrophysical environment of the neutrino propagation. Treating the neutrino interaction with the neutrino filter of the cosmic object as the first, neutrino-spin measurement, whose result is not recorded, we study its invasive effect on the second, neutrino-flavor measurement in the lab. We quantify the invasiveness of the first, blind measurement by means of quantum witness that in the discussed case has an advantage over the well-known Leggett-Garg inequality, since the latter explores two-time correlation functions of the same operator. We solve analytically the Lindblad master equation for time evolution of the neutrino density matrix and on this basis we calculate the quantum witness for measuring cosmic electron neutrinos in the lab. We present numerical illustrations of the robust invasive effect showing that the quantum witness as a function of the distance between Earth and a cosmic object can be an asymptotically nonvanishing quantity despite the thermalization of the neutrino spin induced by stochastic interstellar magnetic fields.

We show that domain walls, or kinks, can be constructed in simple scalar theories where the scalar has no potential. These theories belong to a class of k-essence where the Lagrangian vanishes identically when one lets the derivatives of the scalar vanish. The domain walls we construct have positive energy and stable quadratic perturbations. As particular cases, we find families of theories with domain walls and their quadratic perturbations identical to the ones of the canonical Mexican hat or sine-Gordon scalar theories. We show that canonical and noncanonical cases are nevertheless distinguishable via higher order perturbations or a careful examination of the energies. In particular, in contrast to the usual case, our walls are local minima of the energy among the field configuration having some fixed topological charge, but not global minima.

We study the prompt photon hadroproduction at the LHC with the $k_T$-factorization approach and the $q{g}^{*}\to q\gamma$ and $g^{*}{g}^{*}\to q\overline{q}\gamma$ partonic channels, using three unintegrated gluon distributions which depend on gluon transverse momentum. They represent three different theoretical schemes which are usually considered in the $k_T$-factorization approach, known under the acronyms: KMR, CCFM, and GBW gluon distributions. We find sensitivity of the calculated prompt photon transverse momentum distribution to the gluon transverse momentum distribution. The predictions obtained with the three approaches are compared to data, that allows to differentiate between them. We also discuss the significance of the two partonic channels, confronted with the expectations which are based on the applicability of the $k_T$-factorization scheme in the high energy approximation.

We consider the lepton-number-violating processes in ${\mathrm{\Lambda }}_b/{\mathrm{\Lambda }}_c$ decays mediated by on-shell GeV-scale sterile neutrino. We calculate the branching ratio for the following processes: ${\mathrm{\Lambda }}_b^0\to {\mathcal{B}}^{+}{\mu }^{-}{\mu }^{-}{\pi }^{+}$, where ${\mathcal{B}}^{+}$ is ${\mathrm{\Lambda }}_c^{+}$ or proton, and ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{\mu }^{+}{\mu }^{+}{\pi }^{-}$ as function of the mass of the sterile neutrino $m_N$ and the heavy-light mixing coefficient of the extended Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix $|U_{\mu N}{|}^2$. The effect of finite detector size is included in our calculation. After comparing the theoretical effective branching ratio with the expected experimental ability of LHCb, we give the sensitivity upper bounds on $|U_{\mu N}{|}^2$ on the ($|U_{\mu N}{|}^2-m_N$) plane. These channels give comparable results with the bounds given by different search strategies (e.g., at Belle, NuTeV, DELPHI, and BEBC) in the mass region $m_N\simeq 0.25\mathrm{GeV}–4.5\mathrm{GeV}$, and the limits are stronger in the mass range $2\mathrm{GeV}<m_N<4.5\mathrm{GeV}$.

The Jarlskog invariant which controls the size of intrinsic $CP$ violation in neutrino oscillation appearance experiments is modified by Wolfenstein matter effects for neutrinos propagating in matter. In this paper we give the exact factorization of the Jarlskog invariant in matter into the vacuum Jarlskog invariant times two, two-flavor matter resonance factors that control the matter effects for the solar and atmospheric resonances independently. We compare the location of the minima of the factorizing resonance factors with the location of the solar and atmospheric resonances, precisely defined. They are not identical but the fractional differences are both found to be less than 0.1%. In addition, we explain why symmetry polynomials of the square of the mass of the neutrino eigenvalues in matter, such as inverse of the square of the Jarlskog invariant in matter, can be given as polynomials in the matter potential.

Using data collected with the BESIII detector operating at the Beijing Electron Positron Collider, we search for the process $e^{+}{e}^{-}\to {\eta }_c\eta {\pi }^{+}{\pi }^{-}$. The search is performed using five large datasets recorded at center-of-mass energies of 4.23, 4.26, 4.36, 4.42, and 4.60 GeV. The ${\eta }_c$ meson is reconstructed in 16 exclusive decay modes. No signal is observed in the ${\eta }_c$ mass region at any center-of-mass energy. The upper limits on the reaction cross sections are determined to be 6.2, 10.8, 27.6, 22.6 and 23.7 pb at the 90% confidence level at the center-of-mass energies listed above.

The study of black hole physics revealed a fundamental connection between thermodynamics, quantum mechanics, and gravity. Today, it is known that black holes are thermodynamical objects with well-defined temperature and entropy. Although black hole radiance gives us the mechanism from which we can associate a well-defined temperature to the black hole, the origin of its entropy remains a mystery. Here we investigate how the quantum fluctuations from the fields that render the black hole its temperature contribute to its entropy. By using the exact renormalization group equation for a self-interacting real scalar field in a spacetime possessing a bifurcate Killing horizon, we find the renormalization group flow of the total gravitational entropy. We show that throughout the flow one can split the quantum field contribution to the entropy into a part coming from the entanglement between field degrees of freedom inside and outside the horizon and a part due to the quantum corrections to the Wald entropy coming from the Noether charge. The renormalized black hole entropy is shown to be constant throughout the flow while the balance between the effective black hole entropy at low energies and the infrared entanglement entropy changes. A similar conclusion is valid for the Wald entropy part of the total entropy. Additionally, our calculations show that there is no mismatch between the renormalization of the coupling constants (in particular, the minimal coupling $\xi$ with the scalar curvature) coming from the effective action or the total gravitational entropy, showing that once the theory is renormalized the total gravitational entropy comes out automatically finite.

In this work, a novel mechanism for spontaneous symmetry breaking is presented. This mechanism incorporates gravity in the generation of masses for gauge fields, showing that the Higgs mechanism can take place even without a quartic self-interaction at the fundamental level. Using the scale-dependent effective action ${\mathrm{\Gamma }}_k$ minimally coupled to a gravitational sector, a variational parameter setting is applied. This provides a mass and vacuum expectation value as a function of the constants arising in the low-scale expansion of Newton and cosmological couplings. A comparison with experimental data, such as the Higgs mass, allows putting restrictions on these constants. This generic approach can be compared with explicit candidates for an effective field theory of gravity. As an example, we use the asymptotic safety scenario, where we find restrictions on the matter content of the theory.

We study the gauge invariant ’t Hooft operator in canonical formalism for Yang-Mills theory as well as the $\mathcal{N}=4$ super-Yang-Mills theory with the gauge group $U(N)$. It is shown that the spectrum of the ’t Hooft operator labeled by the arbitrary irreducible representation of the gauge group is the same as the spectrum of the Wilson operator labeled by the same representation. So it is possible to construct a unitary operator $S$ making the two kinds of loop operators transformed into each other. S-duality transformation could be realized by the operator $S$. We compute the supersymmetry variations of the loop operators with the fermionic couplings turned off. The result is consistent with the expectation that the action of $S$ should make supercharges transform with a $U(1{)}_Y$ phase.

We study the effect of compact extra dimensions on the gravitational wave luminosity and waveform. We consider a toy model, with a compactified fifth dimension, and matter confined on a brane. We work in the context of five-dimensional (5D) general relativity, though we do make connections with the corresponding Kaluza-Klein effective 4D theory. We show that the luminosity of gravitational waves emitted in 5D gravity by a binary with the same characteristics (same masses and separation distance) as a 4D binary is 20.8% less relative to the 4D case, to leading post-Newtonian order. The phase of the gravitational waveform differs by 26% relative to the 4D case, to leading post-Newtonian order. Such a correction arises mainly due to the coupling between matter and dilaton field in the effective 4D picture and agrees with previous calculations when we set black holes’ scalar charges to be those computed from the Kaluza-Klein reduction. The above corrections to the waveform and the luminosity are inconsistent with the gravitational-wave and binary pulsar observations, and they thus effectively rule out the possibility of such a simple compactified higher dimensions scenario. We also comment on how our results change if there are several compactified extra dimensions and show that the discrepancy with 4D general relativity only increases.

In this article we analyze the post-Newtonian approximation of a generalization of the symmetric teleparallel gravity with the help of the parametrized post-Newtonian (PPN) formalism. This class of theories is based on a free function of the five independent quadratic contractions of the nonmetricity tensor. By calculating the PPN metric of these theories, we can restrict the Taylor coefficients of the free function with the help of the PPN parameters and their observational bounds. We find two families of theories whose PPN parameters are identical to those of general relativity, and thus in full agreement with observations. For three further families, we find that only the PPN parameters $\beta$ and $\gamma$ deviate, but can be brought arbitrarily close to their general relativity values by an appropriate choice of the Lagrangian, so that also these families contain candidate theories which agree with observations. The remaining theories either possess no well-defined solution of the post-Newtonian field equations, or possess a post-Newtonian limit which exceeds the form assumed in the PPN formalism.

The first direct observations of gravitational waves by the LIGO collaboration have motivated different tests of general relativity (GR), including the search for extra pulses following the GR waveform for the coalescence of compact objects. The motivation for these searches comes from the alternative proposal that the final compact object could differ from a black hole by the lack of an event horizon and a central singularity. Such objects are expected in theories that, motivated by quantum gravity modifications, predict horizonless objects as the final stage of gravitational collapse. In such a hypothetical case, this exotic compact object (ECO) will present a (partially) reflective surface at $r_{\mathrm{ECO}}=r_{+}(1+\epsilon )$, instead of an event horizon at $r_{+}$. For this class of objects, an in-falling wave will not be completely lost and will give rise to secondary pulses, to which recent literature refers as echoes. However, the largely unknown ECO reflectivity is determinant for the amplitude of the signal, and details also depend on the initial conditions of the progenitor compact binary. Here, for the first time, we obtain estimates for the detectability of the first echo, using a perturbative description for the inspiral-merger-ringdown waveform and a physically motivated ECO reflectivity. Binaries with comparable masses will have a stronger first echo, improving the chances of detection. For a case like GW150914, the detection of the first echo will require a minimum ringdown signal-to-noise ratio (SNR) in the range $\sim 20–60$. The most optimistic scenario for echo detection could already be probed by LIGO in the next years. With the expected improvements in sensitivity we estimate one or two events per year to have the required SNR for the first echo detection during O4.

We present a new action which reproduces the cosmological sector of general relativity in both the Friedmann-Lemaître-Robertson-Walker and Bianchi models. This action makes no reference to the scale factor and is of a frictional type first examined by Herglotz. We demonstrate that the extremization of this action reproduces the usual dynamics of physical observables, and the symplectification of this action is the Einstein-Hilbert action for cosmological models. We end by discussing some of the increased explanatory power produced by considering the reduced physical ontology resulting from eliminating scale.

We perform a joint analysis of the counts of redMaPPer clusters selected from the Dark Energy Survey (DES) year 1 data and multiwavelength follow-up data collected within the $2500{\mathrm{deg}}^2$ South Pole Telescope (SPT) Sunyaev-Zel’dovich (SZ) survey. The SPT follow-up data, calibrating the richness-mass relation of the optically selected redMaPPer catalog, enable the cosmological exploitation of the DES cluster abundance data. To explore possible systematics related to the modeling of projection effects, we consider two calibrations of the observational scatter on richness estimates: a simple Gaussian model which account only for the background contamination (BKG), and a model which further includes contamination and incompleteness due to projection effects (PRJ). Assuming either a $\mathrm{\Lambda }\mathrm{CDM}+\sum m_{\nu }$ or $w\mathrm{CDM}+\sum m_{\nu }$ cosmology, and for both scatter models, we derive cosmological constraints consistent with multiple cosmological probes of the low and high redshift Universe, and in particular with the SPT cluster abundance data. This result demonstrates that the DES Y1 and SPT cluster counts provide consistent cosmological constraints, if the same mass calibration data set is adopted. It thus supports the conclusion of the DES Y1 cluster cosmology analysis which interprets the tension observed with other cosmological probes in terms of systematics affecting the stacked weak lensing analysis of optically selected low–richness clusters. Finally, we analyze the first combined optically SZ selected cluster catalog obtained by including the SPT sample above the maximum redshift probed by the DES Y1 redMaPPer sample ($z=0.65$). Besides providing a mild improvement of the cosmological constraints, this data combination serves as a stricter test of our scatter models: the PRJ model, providing scaling relations consistent between the two abundance and multiwavelength follow-up data, is favored over the BKG model.

There have been recent attempts at justifying, from first principles, and within the standard framework, the emergence of classical behavior in the postinflationary cosmological context. Accounting for this emergence is an important issue, as it underlies the extraordinary empirical success of our current understanding of cosmology. In this work, we offer a critique of different efforts at explaining the emergence of classical behavior in cosmology within the standard framework. We argue that such endeavors are generically found lacking in conceptual clarity, as they invariably rely, either upon unjustified, implicit assumptions, or on circular logic. We conclude that, within the standard approach, the emergence of classical behavior in cosmology constitutes an unexplained phenomenon.

Gravitational waves can provide an accurate measurement of the luminosity distance to the source but cannot provide the source redshift unless the degeneracy between mass and redshift can be broken. This makes it essential to infer the redshift of the source independently to measure the expansion history of the Universe. We show that by exploiting the clustering scale of the gravitational wave sources with galaxies of a known redshift, we can infer the expansion history from redshift unknown gravitational wave sources. By using gravitational wave sources of unknown redshift that are detectable from the network of gravitational wave detectors with Advanced LIGO design sensitivity, we will be able to obtain accurate and precise measurements of the local Hubble constant, the expansion history of the Universe, and the gravitational wave bias parameter, which captures the distribution of gravitational wave sources with respect to the redshift tracer distribution. While we showcase its application to low redshift gravitational waves, this technique will be applicable also to the high redshift gravitational wave sources detectable from Laser Interferometer Space Antenna (LISA), Cosmic Explorer (CE), and Einstein Telescope (ET). Moreover, this method will also be applicable to samples of supernovae and fast radio bursts with unknown or photometric redshifts.

Neutron stars could contain a mixture of ordinary nuclear matter and dark matter, such that dark matter could influence observable properties of the star, such as its mass and radius. We study these dark matter admixed neutron stars for two choices of dark matter: a free Fermi gas and mirror dark matter. In addition to solving the multifluid Tolmon-Oppenheimer-Volkoff equations for static solutions and presenting mass-radius diagrams, we focus on two computations that are lacking in the literature. The first is a rigorous determination of stability over the whole of parameter space, which we do using two different methods. The first method is based on harmonic time-dependent perturbations to the static solutions and on solving for the radial oscillation frequency. The second method, which is less well-known, conveniently makes use of unperturbed, static solutions only. The second computation is of the radial oscillation frequency, for fundamental modes, over large swaths of parameter space.

In future geocentric space-based gravitational-wave observatory missions, eclipses due to passing through the Moon’s and Earth’s shadows can negatively impact the sciencecraft’s thermal stability and steady power supply. The occurrence should be reduced as much as possible in orbit design. In regard to TianQin’s circular high orbits, we tackle the combined challenges of avoiding eclipses and stabilizing the nearly equilateral-triangle constellation. Two strategies are proposed, including initial phase selection and orbit resizing to $1:8$ synodic resonance with the Moon, where the latter involves slightly raising TianQin’s preliminary orbital radius of $1\times {10}^5\mathrm{km}$ to $\sim 100900\mathrm{km}$. As the result, we have identified pure-gravity target orbits with a permitted initial phase range of $\sim 15°$, which can maintain eclipse-free during the $3+3$ month observation windows throughout a 5-year mission started in 2034, and meanwhile fulfill the constellation stability requirements. Thereby the eclipse issue for TianQin can be largely resolved.

In the framework of the type II two-Higgs-doublet model with a singlet scalar dark matter $S$, we study the dark matter observables, the electroweak phase transition, and the gravitational wave signals by such strongly first order phase transition after imposing the constraints of the LHC Higgs data. We take the heavy $CP$-even Higgs boson $H$ as the only portal between the dark matter and standard model (SM) sectors, and find that the LHC Higgs data and dark matter observables require $m_S$ and $m_H$ to be larger than 130 GeV and 360 GeV for $m_A=600\mathrm{GeV}$ in the case of the 125 GeV Higgs boson with the SM-like coupling. Next, we carve out some parameter space where a strongly first order electroweak phase transition can be achieved, and find benchmark points for which the amplitudes of gravitational wave spectra reach the sensitivities of the future gravitational wave detectors.