We consider the observational signatures of reflective naked singularities as seen by the current and next-generation Event Horizon Telescope (EHT). The reflective naked singularities lead to a distinctive morphology of their accretion disk images producing a series of bright rings at the central part of the image. We explore the capacity of the present and near-future EHT arrays to detect this structure considering two particular naked singularity spacetimes and modeling the galactic target $\mathrm{M}{87}^{*}$. We obtain that the 2017 EHT array is incapable of resolving the bright ring series. However, it detects an increased overall intensity of the central brightness depression reaching with an order of magnitude higher values than for the Kerr black hole. This metric can be used as a quantitative measure for the absence of an event horizon. The observations with the next-generation EHT at 230 GHz would reveal 2 orders of magnitude difference in the intensity of the central brightness depression between naked singularities and black holes. Introducing a second observational frequency at 345 GHz would already resolve qualitative effects in the morphology of the disk image for naked singularities as certain bright spots become apparent at the center of the image.

Motivated by the aim of producing significant number of primordial black holes, over the past few years, there has been a considerable interest in examining models of inflation involving a single, canonical field, that permit a brief period of ultraslow roll. Earlier, we had examined inflationary magnetogenesis—achieved by breaking the conformal invariance of the electromagnetic action through a coupling to the inflaton—in situations involving departures from slow roll. We had found that a transition from slow roll to ultraslow roll inflation can lead to a strong blue tilt in the spectrum of the magnetic field over small scales and also considerably suppress its strength over large scales. In this work, we consider the scenario of pure ultraslow roll inflation and show that scale invariant magnetic fields can be obtained in such situations with the aid of a nonconformal coupling function that depends on the kinetic energy of the inflaton. Apart from the power spectrum, an important probe of the primordial magnetic fields are the three-point functions, specifically, the cross-correlation between the curvature perturbations and the magnetic fields. We calculate the three-point cross-correlation between the curvature perturbations and the magnetic fields in pure ultraslow roll inflation for the new choice of the nonconformal coupling function. In particular, we examine the validity of the consistency condition that is expected to govern the three-point function in the squeezed limit and comment on the wider implications of the results we obtain.

Analysis of microwave sky signals, such as the cosmic microwave background, often requires component separation using multifrequency methods, whereby different signals are isolated according to their different frequency behaviors. Many so-called blind methods, such as the internal linear combination (ILC), make minimal assumptions about the spatial distribution of the signal or contaminants, and only assume knowledge of the frequency dependence of the signal. The ILC produces a minimum-variance linear combination of the measured frequency maps. In the case of Gaussian, statistically isotropic fields, this is the optimal linear combination, as the variance is the only statistic of interest. However, in many cases the signal we wish to isolate, or the foregrounds we wish to remove, are non-Gaussian and/or statistically anisotropic (in particular for the case of Galactic foregrounds). In such cases, it is possible that machine learning (ML) techniques can be used to exploit the non-Gaussian features of the foregrounds and thereby improve component separation. However, many ML techniques require the use of complex, difficult-to-interpret operations on the data. We propose a hybrid method whereby we train an ML model using only combinations of the data that do not contain the signal, and combine the resulting ML-predicted foreground estimate with the ILC solution to reduce the error from the ILC. We demonstrate our methods on simulations of extragalactic temperature and Galactic polarization foregrounds and show that our ML model can exploit non-Gaussian features, such as point sources and spatially varying spectral indices, to produce lower-variance maps than ILC—e.g., reducing the variance of the B-mode residual by factors of up to 5—while preserving the signal of interest in an unbiased manner. Moreover, we often find improved performance even when applying our ML technique to foreground models on which it was not trained.

We explore full-shape analysis with simulation-based priors, which is the simplest approach to galaxy clustering data analysis that combines effective field theory (EFT) on large scales and numerical simulations on small scales. The core ingredient of our approach is the prior density of EFT parameters which we extract from a suite of 10,500 galaxy simulations based on the halo occupation distribution (HOD) model. We measure the EFT parameters with the field-level forward model, which enables us to cancel cosmic variance. On the theory side, we develop a new efficient approach to calculate field-level transfer functions using time-sliced perturbation theory and the logarithmic fast Fourier transform. We find that the cosmology dependence of EFT parameters of galaxies is approximately degenerate with the HOD parameters, and hence it can be ignored for the purpose of prior generation. We use neural density estimation to model the measured distribution of EFT parameters. Our distribution model is then used as a prior in a reanalysis of the Baryon Oscillation Spectroscopic Survey (BOSS) full-shape galaxy power spectrum data. Assuming the $\mathrm{\Lambda }\mathrm{CDM}$ model, we find significant ($\approx 30\%$ and $\approx 60\%$) improvements for the matter density fraction and the mass fluctuation amplitude, which are constrained to ${\mathrm{\Omega }}_m=0.315\pm 0.010$ and ${\sigma }_8=0.671\pm 0.027$. The value of the Hubble constant does not change, $H_0=68.7\pm 1.1\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$. This reaffirms earlier reports of the structure growth tension from the BOSS data. Finally, we use the measured EFT parameters to constrain the galaxy-dark matter connection.

A relativistic MOND theory, promising in reproducing cosmology as well as the MOND phenomenology in the low acceleration regime, was recently proposed. We present the post-Newtonian (PN) approximation and relativistic perturbation equations of this theory in cosmological context. The PN equations are presented to 1PN order and perturbation equations are presented in fully-nonlinear and exact forms. The gauge issues are clarified. The 1PN equations and linear perturbation equations are presented without imposing temporal gauge conditions. We show that to 0PN order baryon perturbation grows faster in the MOND regime. The MOND field can be interpreted as a fluid with specific equation of state without anisotropic stress, and the Jeans criterion is derived for the MOND field.

We have discussed in detail how neutrinos produced from inflaton solely through gravitational interaction can successfully reheat the Universe. For this, we have introduced the well-known type-I seesaw neutrino model. Depending on seesaw model parameters, two distinct reheating histories have been realized and dubbed as (i) Neutrino dominating: Following the inflaton domination, the universe becomes neutrino dominated, and their subsequent decay concludes the reheating process, and (ii) Neutrino heating: Despite being subdominant compared to inflaton energy, neutrinos efficiently heat the thermal bath and produce the radiation dominated universe. Imposing baryon asymmetric yield, the $\mathrm{\Delta }{N}_{\mathrm{eff}}$ constraint at big bang nucleosynthesis (BBN) considering primordial gravitational waves (PGW), we have arrived at the following constraints on reheating equation of state to lie within $0.5\lesssim w_{\varphi }\lesssim 1.0$. In these neutrino-driven reheating backgrounds, we further performed a detailed analysis of both thermal and nonthermal production of dark matter (DM), invoking two minimal models, namely the Higgs portal DM and classical quantum chromodynamics pseudoscalar axion. An interesting correlation between seemingly uncorrelated DM and type-I seesaw parameters has emerged when confronting various direct and indirect observations. When DMs are set to freeze-in, freeze-out, or oscillate during reheating, new parameter spaces open, which could be potentially detectable in future experiments, paving an indirect way to look into the early Universe in the laboratory.

We study in detail the fully inhomogeneous nonlinear dynamics of axion inflation, identifying three regimes: weak, mild, and strong backreaction, depending on the duration of inflation. We use lattice techniques that explicitly preserve gauge invariance and shift symmetry, and which we validate against other computational methods of the linear dynamics and of the homogeneous backreaction regime. Notably, we demonstrate that the latter fails to accurately describe the truly local dynamics of strong backreaction. We investigate the convergence of simulations of local backreaction, determining the requirements to achieve an accurate description of the dynamics, and providing useful parametrizations of the delay of the end of inflation. Additionally, we identify key features emerging from a proper local treatment of strong backreaction: the dominance of magnetic energy against the electric counterpart, the excitation of the longitudinal mode, and the generation of a scale-dependent chiral (im)balance. Our results underscore the necessity to accurately capture the local nature of the nonlinear dynamics of the system, in order to correctly assess phenomenological predictions, such as, e.g., the production of gravitational waves and primordial black holes.

Several pulsar timing array (PTA) collaborations have recently found evidence for a gravitational wave background (GWB) permeating our Galaxy. The origin of this background is still unknown. Indeed, while the gravitational wave emission from inspiraling supermassive black hole binaries (SMBHB) is the primary candidate for its origin, several cosmological sources have also been proposed. One distinctive feature of SMBHB-generated backgrounds is the presence of GWB anisotropies stemming from the binaries distribution in the local Universe. However, none of the anisotropy searches performed to date reported a detection. In this work, we show that the lack of anisotropy detection is not currently in tension with a SMBHB origin of the background. We accomplish this by calculating the probability for present and future PTAs to observe deviations from an isotropic GWB. We find that a PTA with the noise characteristics of the NANOGrav 15-year data set had only a 2%–11% probability of detecting deviations from isotropy in an SMBHB-generated GWB, depending on the properties of the SMBHB population. However, we estimate that for the IPTA DR3 data set these probabilities will increase to 4%–28%, putting more pressure on the SMBHB interpretation in case of a null detection. We also identify SMBHB populations that are more likely to produce significant deviations from isotropy. This information could be used together with the spectral properties of the GWB to characterize the SMBHB population.

The announcement in the summer of 2023 about the discovery of evidence for a gravitational-wave background (GWB) using pulsar timing arrays (PTAs) ignited interest in both the PTA and larger scientific communities about the experiment itself and the scientific implications of its findings. As a result, numerous scientific works have been published analyzing and further developing various aspects of the experiment, from performing tests of gravity to improving the efficiency of the current data analysis techniques. In this regard, we contribute to the recent advancements in the field of PTAs by presenting the most general, agnostic, per-frequency Bayesian search for a low-frequency (red) noise process in these data. Our new method involves the use of a conjugate Jeffreys-like multivariate prior, which allows one to model all unique parameters of the global PTA-level red-noise covariance matrix as a separate model parameter for which a marginalized posterior-probability distribution can be found using Gibbs sampling. Even though perfecting the implementation of the Gibbs sampling and mitigating the numerical stability challenges require further development, we show the power of this new method by analyzing realistic and theoretical PTA simulated data sets. We show how our technique is consistent with the more restricted standard techniques in recovering both the auto and cross spectra of pulsars’ low-frequency (red) noise. Furthermore, we highlight ways to approximately characterize a GWB (both its auto and cross spectra) using Fourier coefficient estimates from single-pulsar and so-called common uncorrelated red-noise analyses via analytic draws from a specific inverse Wishart distribution.

The detection of GW170817/GRB170817A implied a strong association between short gamma-ray bursts (SGRBs) and binary neutron star (BNS) mergers which produce gravitational waves (GWs), opening a new window for multimessenger observations. The upcoming High Altitude Detection of Astronomical Radiation (HADAR) experiment, remarkable for its wide field of view and its large effective area above tens of GeV, will enable the prompt detection of very high-energy (VHE; $>10\mathrm{GeV}$) SGRBs. The aim of this paper is to explore GW/SGRB joint detections by future GW detector networks in synergy with HADAR, including the second-generation LIGO (Livingston, Hanford, and future India), Virgo, and KAGRA, and the third-generation ET and CE. For SGRB detections, we inherit the model from our previous work on short GRBs, with an adjustment of the jet structure. We adopt a phenomenological model to describe the GWs produced by BNSs and detected by the network of interferometers. We compute theoretical detection efficiency functions of GW detector networks, and we simulate pseudodetections by Monte Carlo sampling. We check that our predictions are in agreement with the actual detections of LIGO-Virgo in the O2 and O3 observing runs. The joint detection of GW/SGRBs is then discussed, including their parameter correlations, triggered GW thresholds, and joint detection skymaps. The estimated joint detection rates are $0.3–3.3{\mathrm{yr}}^{-1}$ for a LHVKI–HADAR network with different parameters and possible configurations, and they range from 0.4 to $4.7{\mathrm{yr}}^{-1}$ for a $\mathrm{ET}+\mathrm{CE}$–HADAR network.

In recent years, energy correlators have emerged as powerful observables for probing the fragmentation dynamics of high-energy collisions. We introduce the first numerical strategy for calculating energy correlators using the Hamiltonian lattice approach, providing access to the intriguing nonperturbative dynamics of these observables. Furthermore, motivated by rapid advances in quantum computing hardware and algorithms, we propose a quantum algorithm for calculating energy correlators in quantum field theories. This algorithm includes ground state preparation, the application of source, sink, energy flux and real-time evolution operators, and the Hadamard test. We validate our approach by applying it to the SU(2) pure gauge theory in $2+1$ dimensions on $3\times 3$ and $5\times 5$ honeycomb lattices with $j_{\max }=\frac{1}{2}$ at various couplings, utilizing both classical methods and the quantum algorithm, the latter tested using the IBM emulator for specific configurations. The results are consistent with the expected behavior of the strong coupling regime and motivate a more comprehensive study to probe the confinement dynamics across the weak and strong coupling regimes.

Neutrinos elastically scattered off atomic electrons offer a unique opportunity to probe the Standard Model (SM) and beyond SM physics. In this work, we examine the new physics effects of light mediators through elastic neutrino-electron scattering using solar neutrinos at the low energy range of PandaX-4T. These mediators, with a mass less than 1 GeV, are common properties of extensions to the SM. Accordingly, we consider universal light mediator models involving scalar, vector, and tensor interactions allowed by Lorentz invariance, and the anomaly-free $U(1{)}^{\prime }$ extensions of the SM with a new vector mediator such as the $L_e-L_{\mu }$, $L_e-L_{\tau }$ and $L_{\mu }-L_{\tau }$ gauge models in which the charges are exclusively leptonic. The new physics effects are analyzed by embedding each model into the SM process using solar neutrino flux. We obtain novel constraints on the coupling-mass plane of these models from the latest Run0 and Run1 datasets of the PandaX-4T experiment. We also compare our results with other limits derived from various terrestrial and astrophysical experiments. Our analysis results reveal more stringent limits in some regions of parameter space.

Axion or axionlike particles are one of the leading candidates for dark matter. Because of its tiny coupling with photons, axion dark matter in the background can induce distinct phase velocities for light with different parity, an effect known as birefringence. Here, we propose a modification to the polarization state of the interspacecraft laser link in Laser Interferometer Space Antenna (LISA)-like interferometers to make them sensitive to this birefringence effect. We discuss the prospects of using the Sagnac combinations to search for axion dark matter and derive the corresponding sensitivity. With this setup, we show that next-generation laser interferometers in space would have promising sensitivities on the axion-photon coupling with axion mass around ${10}^{-19}-{10}^{-14}\mathrm{eV}$.

While much supersymmetric weakly interacting massive particle (WIMP) parameter space has been ruled out, one remaining important candidate is Higgsino dark matter. The Higgsino can naturally realize the “inelastic dark matter” scenario, where the scattering off a nucleus occurs between two nearly-degenerate states, making it invisible to WIMP direct detection experiments if the splitting is too large to be excited. It was realized that a “luminous dark matter” detection process, where the Higgsino upscatters in the Earth and subsequently decays into a photon in a large neutrino detector, offers the best sensitivity to such a scenario. We consider the possibility of adding a large volume of a heavy element, such as Pb or U, around the detector. We also consider the presence of U and Th in the Earth itself, and the effect of an enhanced high-velocity tail of the dark matter distribution due to the presence of the Large Magellanic Cloud. These effects can significantly improve the sensitivity of detectors such as JUNO, $\mathrm{SNO}+$, KamLAND, and Borexino, potentially making it possible in the future to cover much of the remaining parameter space for this classic supersymmetric WIMP dark matter.

The Belle II collaboration recently announced that they observed the $B^{+}\to K^{+}\nu \overline{\nu }$ decay process for the first time. However, their result encounters a $2.7\sigma$ deviation from the Standard Model (SM) calculation. Additionally, Fermilab released new data on muon $g-2$ away from the SM expectation with $5.1\sigma$. In this paper, we study the simplest UV-complete $\mathrm{U}(1{)}_{{\mathsf{L}}_{\mu }-{\mathsf{L}}_{\tau }}$-charged complex scalar dark matter (DM) model. Thanks to the existence of light dark Higgs boson and light dark photon, we can explain the observed relic density of DM and resolve the results reported by both Belle II and Fermilab experiments simultaneously. As a by-product, the Hubble tension can be alleviated by taking $\mathrm{\Delta }{N}_{\mathsf{eff}}\simeq 0.3$ induced by the light dark photon, which could be tested by CMB stage-4 and new NA64 experimental data in the near future. In addition, our light DM mass is highly testified by future data released by Belle II and CMB stage-4.

We survey the opportunities offered by the detection of the forward muons that accompany the creation of neutral effective vector bosons at a muon collider, in different kinematic regimes. Vectors with relatively low energy produce the Higgs boson and the extended muon angular coverage enables studies of the Higgs properties, such as the measurement of the inclusive production cross section and the branching ratio to invisible final states. New heavy particles could be produced by vectors of higher energy, through Higgs portal interactions. If the new particles are invisible, the detection of the forward muons is essential in order to search for this scenario. The angular correlations of the forward muons are sensitive to the quantum interference between the vector-boson helicity amplitudes and can be exploited for the characterization of vector-boson scattering and fusion processes. This is illustrated by analyzing the $CP$ properties of the Higgs coupling to the $Z$ boson. Our findings provide a physics case and a set of benchmarks for the design of a dedicated forward muon detector.

We present a study on the possibility of observing a hypothetical particle known as the flavon $H_F$, which is predicted in an extension of the standard model that includes the so-called Froggatt-Nielsen mechanism. The proposed decay channel is through a $b\overline{b}h$ final state, where the Higgs boson ($h$) decays to a pair of photons or a pair of $b$ quarks $(h\to \gamma \gamma ,b\overline{b})$. We found that, under special scenarios of the model parameter space, the processes analyzed could provide evidence for the existence of the flavon in the next stage of the LHC: the High Luminosity LHC. Specifically, we predict a signal significance of $5\sigma$ ($2\sigma$) in the $h\to b\overline{b}$ ($h\to \gamma \gamma$) channel for a flavon mass of 800 (900) GeV and an integrated luminosity of 2500 $(3000){\mathrm{fb}}^{-1}$.

We discuss a simple theory for physics beyond the Standard Model where a Majorana dark matter is predicted from anomaly cancellation. We discuss in detail the minimal theory where the baryon number is a local symmetry spontaneously broken at the low scale. The correlation between the cosmological constraints on the dark matter relic density, the direct detection and collider bounds is investigated. We discuss in great detail the gamma lines from dark matter annihilation showing the possibility to test these predictions in the near future at gamma-ray telescopes such as CTA. We investigate all processes contributing to the total photon flux from dark matter annihilation and point out the unique features that can be used to test this theory for dark matter.

Many exotic charmoniumlike mesons have already been discovered experimentally, of which the $Z_c$ mesons with isospin 1 are prominent examples. We investigate $J^{PC}=1^{+\pm }$ states with flavor $\overline{c}c\overline{q}q$ ($q=u$, $d$) in isospin 1 using lattice QCD. This is the first study of these mesons employing more than one volume and involving frames with nonzero total momentum. We utilize two $N_f=2+1$ CLS ensembles with $m_{\pi }\simeq 280\mathrm{MeV}$. The simulations are performed with unphysical light quark masses at a single lattice spacing of $a\simeq 0.086\mathrm{fm}$ and omit $\psi (2S)\pi$, $\psi (3770)\pi$ and three-particle decay channels, so our results provide only qualitative insights. Resulting eigenenergies are compatible or just slightly shifted down with respect to noninteracting energies, where the most significant shifts occur for certain $D{\overline{D}}^{*}$ states. Both channels $1^{+\pm }$ have a virtual pole slightly below the threshold if $D{\overline{D}}^{*}$ is assumed to be decoupled from other channels. In addition, we perform a coupled channel analysis of $J/\psi \pi$ and $D{\overline{D}}^{*}$ scattering with $J^{PC}=1^{+-}$ within an effective field theory framework. The $J/\psi \pi$ and $D{\overline{D}}^{*}$ invariant-mass distributions from BESIII and finite-volume energies from several lattice QCD simulations, including this work, are fitted simultaneously. All fits yield two poles relatively close to the $D{\overline{D}}^{*}$ threshold and reasonably reproduce the experimental $Z_c$ peaks. They also reproduce lattice energies up to slightly above the $D{\overline{D}}^{*}$ threshold, while reproduction at even higher energies is better for fits that put more weight on the lattice data. Our findings suggest that the employed effective field theory can reasonably reconcile the peaks in the experimental line shapes and the lattice energies, although those lie close to noninteracting energies. We also study $J/\psi \pi$ scattering in s wave and place upper bounds on the phase shift.

A comprehensive analysis of all available data on cross sections and spin-dependent observables for the $\gamma p\to K^{+}{\mathrm{\Sigma }}^0(1385)$, $\gamma n\to K^{+}{\mathrm{\Sigma }}^{-}(1385)$, and ${\pi }^{+}p\to K^{+}{\mathrm{\Sigma }}^{+}(1385)$ reactions is performed within an effective Lagrangian framework. In addition to the $s$-channel $N$ exchange, $t$-channel $K$ and $K^{*}$ exchanges, $u$-channel $\mathrm{\Lambda }$, $\mathrm{\Sigma }$, and ${\mathrm{\Sigma }}^{*}$ exchanges, and the interaction current, the $s$-channel contributions from a minimal set of $N$ and $\mathrm{\Delta }$ resonances are included in constructing the reaction amplitudes to describe the data. The analysis reveals that all available data for both photon- and hadron-induced $K\mathrm{\Sigma }(1385)$ production reactions can be simultaneously and satisfactorily reproduced when the contribution of the $s$-channel $\mathrm{\Delta }(1930){5/2}^{-}$ resonance is taken into account. The reaction mechanisms, particularly the resonance contributions in each considered reaction, are thoroughly analyzed and discussed in detail.