In the energy-momentum squared gravity (EMSG), the matter energy-momentum tensor is not conserved due to nonminimal interaction between the usual and modified matter fields. For this reason, the $N$-body acceleration may host the EMSG effects that can be probed at the solar scale by the perihelion shift of the planets and experimental tests of the strong equivalence principle (SEP). To shed light on it, in this paper, we present the $N$-body equations of motion in the weak-field limit of the EMSG theory. To do so, the post-Newtonian (PN) hydrodynamic equations, the viral identities, as well as the corresponding equilibrium conditions are introduced in this theory. Armed with these relations, we derive the dynamics of the $N$-body system and its PN interbody metric. It is shown that the EMSG theory is not ruled out by the classical test, the perihelion advance of Mercury, and the test of SEP. In other words, in the first PN order, it is not possible to constrain the free parameter of this theory and even distinguish it from general relativity (GR) using these local tests.

Several theoretical waveform models have been developed over the years to capture the gravitational-wave emission from the dynamical evolution of compact binary systems of neutron stars and black holes. As ground-based detectors improve their sensitivity at low frequencies, the real-time computation of these waveforms can become computationally expensive, exacerbating the steep cost of rapidly reconstructing source parameters using Bayesian methods. This paper describes an efficient numerical algorithm for generating high-fidelity interpolated compact binary waveforms at an arbitrary point in the signal manifold by leveraging computational linear algebra techniques such as singular value decomposition and the meshfree approximation. The results are presented for the time-domain NRHybSur3dq8 inspiral-merger-ringdown waveform model that is fine-tuned to numerical relativity simulations and parametrized by the two component-masses and two aligned spins. For demonstration, we target a specific region of the intrinsic parameter space inspired by the previously inferred parameters of the GW200311_115853 event, a binary black hole system whose merger was recorded by the network of Advanced LIGO and Virgo detectors during the third observation run. We show that the meshfree interpolated waveforms can be evaluated in $\sim 2.3\mathrm{ms}$, which is about 38 times faster than its brute-force (frequency-domain tapered) implementation in the pycbc software package at a median accuracy of $\sim \mathcal{O}({10}^{-5})$. The algorithm is computationally efficient and scales favorably with an increasing number of dimensions of the parameter space. This technique may find use in rapid parameter estimation and source reconstruction studies.

Convincing evidence of a stochastic gravitational wave (GW) background has been found by the NANOGrav Collaboration in the 15-year data set. From this signal, we can evaluate the possibility of its source being from the early Universe through the tensor perturbations induced by a massive spin-2 graviton field. We consider a time-dependent model of the minimal theory of massive gravity and find values of the graviton mass, mass cutoff time, and Hubble rate of inflation that amplify the energy spectra of primordial GWs sufficiently to reproduce the signal from the NANOGrav data within 1-3 standard deviation. However, a suppression mechanism for high-frequency modes must be introduced to conservatively obey the big bang nucleosynthesis (BBN) bound. While there are regions of the parameter space that reproduce the signal, it remains a challenge to simultaneously respect the BBN and cosmic microwave background bounds without making the graviton mass cutoff time too deep into the matter-dominated era.

Ongoing or soon to come cosmological large-scale structure surveys such as DESI, SPHEREx, Euclid, or the High-Latitude Spectroscopic Survey of the Nancy Grace Roman Space Telescope promise unprecedented measurement of the clustering of galaxies on large scales. When quantified with the Cartesian Fourier basis, the measurement of these large scales requires the introduction of so-called wide-angle corrections. By contrast, the measurement of the power spectrum in a spherical Fourier Bessel (SFB) basis does not require such corrections and naturally accounts for the spherical survey geometries. Here, we develop and implement a fast code to construct the SFB power spectrum and investigate how line of sight effects, physics such as non-Gaussianity, and differing survey geometries affect SFB power spectrum estimates. We then leverage our program to predict the tightness of cosmological constraints from realistic survey specifications using a Fisher matrix formalism.

We perform a thorough analysis of de Sitter solutions in $\mathrm{O}(d,d)$ invariant cosmologies. Starting with a homogeneous and isotropic framework we examine conditions for the existence of such solutions to the vacuum field equations, nonperturbative in ${\alpha }^{\prime }$ in both the string frame and the Einstein frame. We elucidate the nature of the instability in the string frame vacuum. For the Einstein frame, we demonstrate that the de Sitter solutions cannot be eternal. We then extend our analysis to include Bianchi I universes where the $\mathrm{O}(d,d)$ symmetry includes scale factor exchange as well as scale factor duality. We show how the theory can be extended to the anisotropic case so that it admits de Sitter solutions, noting the crucial role played by the $\mathrm{O}(d,d)$ symmetry in satisfying any additional constraints.

The Universe may contain sufficiently small size matter-antimatter domains at temperatures of a few hundred MeV, without violating the success of big bang nucleosynthesis. We demonstrate that this possibility enhances the keV scale sterile neutrino production and may lead to its abundance consistent with the observable energy density of dark matter (DM). Assuming that the quantum chromodynamics (QCD) phase transition is of the first order we argue that it may lead to the separation of matter and antimatter, creating temporarily macroscopic domains occupied by hadronic matter and quark-gluon plasma. In these domains an excess of baryons over antibaryons and vice versa largely can exceed the average baryon and lepton asymmetries of the Universe. We discuss several scenarios of matter-antimatter separation at the QCD phase transition and the production of DM sterile neutrinos in each of them. One of the possibilities requires the presence of lepton asymmetry of the Universe, which can be smaller than that needed for the DM correct abundance in the homogeneous case. Another, the more speculative one, is related to the Omnes phase transition and does not require lepton asymmetries.

Measurements of the cosmic redshift drift—the change in redshift of a source over time—will enable independent detection of cosmological expansion thanks to the immense precision soon reached by new facilities such as the Square Kilometer Array (SKA) Observatory and the Extremely Large Telescope (ELT). We conduct the first ever redshift drift computations in fully relativistic cosmological simulations, with the simulations performed with the einstein toolkit. We compute the redshift drift over the full skies of 50 synthetic observers in the simulation. We compare all-sky averages for each observer—and across all observers—to the Einstein–de Sitter (EdS) model which represents the large-scale spatially averaged space-time of the simulation. We find that at $z\approx 0.2$ the mean redshift drift across the sky for all 50 observers deviates from the EdS prediction at the percent level, reducing to $\sim 0.1\%$ by $z\approx 1$. However, fluctuations in the redshift drift across the sky are $\sim 10\%–30\%$ at $z\approx 0.1$ and a few percent at $z\approx 0.5$. Such fluctuations are large enough to potentially exceed the expected precision of upcoming redshift drift measurements. Additionally, we find that along 0.48% of the light rays, the redshift drift becomes temporarily positive at very low redshift of $z\lesssim 0.02$. This occurs despite our simulation data being based on a matter-dominated model universe. By including a cosmological constant, we do expect a slower growth of structures than in the leading-order EdS space-time, and this may reduce the anisotropy over the observers’s skies, although we generally expect our results to hold as order-of-magnitude estimates. Redshift drift is arguably one of the most important measurements to be made by next-generation telescopes. Our results collectively serve as preparation for interpreting such a measurement in the presence of realistic cosmic structures.

We develop and apply a new framework for reconstructing the ionization history during the epoch of recombination with combinations of cosmic microwave background (CMB), baryon acoustic oscillation (BAO) and supernova data. We find a wide range of ionization histories that are consistent with current CMB data, and also that cosmological parameter constraints are significantly weakened once freedom in recombination is introduced. BAO data partially break the degeneracy between cosmological parameters and the recombination model, and are therefore important in these reconstructions. The 95% confidence upper limits on $H_0$ are 80.1 (70.7) km/s/Mpc given CMB ($\mathrm{CMB}+\mathrm{BAO}$) data, assuming no other changes are made to the standard cosmological model. Including Cepheid-calibrated supernova data in the analysis drives a preference for nonstandard recombination histories with visibility functions that peak early and exhibit appreciable skewness. Forthcoming measurements from the South Pole Telescope will reduce the uncertainties in our reconstructions by about a factor of 2.

Detecting midinfrared (MIR) radiation has significant astronomical applications, although limited by unsatisfactory MIR detectors. Here we reported on the realization of a MIR up-conversion interferometer based on synthetic long base-line in the laboratory. The experimental system consisted of an interferometer and subsequent up-conversion detection part of midinfrared signal, which streamlined the structure and enhanced the reliability of the system. By using a tungsten filament lamp as an imitated star, we not only achieved the single target angle resolution of $1.10\times {10}^{-4}\mathrm{rad}$, but also obtained the field angle resolution of $3.0\times {10}^{-4}\mathrm{rad}$ of double star targets. The angular resolution is in inverse proportion to the length of baseline. The maximum length of simulated baseline in the laboratory is about 3 cm. In a Keck interferometer liked program, the base line can reach up to 85 m leading to a corresponding angular resolution of $3\times {10}^{-9}\mathrm{rad}$ (about 1.8 mas). The study will offer potential benefits in extending the usage of midinfrared light in astronomical exploration.

We analyze the implications of information about local derivatives from the mass-radius diagram in neutron star matter. It is expected that the next generation of gravitational wave and electromagnetic detectors will allow the determination of the neutron star radius and mass with a small uncertainty. Observations of neutron stars clustered around a given neutron star mass allow the estimation of local derivatives in the $M(R)$ diagram, which can be used to constrain neutron star properties. From a model-independent description of the neutron star equation of state, it is shown that a $M(R)$ curve with a negative slope at $1.4M_{\odot }$ predicts a $2M_{\odot }$ neutron star radius below 12 km. Furthermore, a maximum mass below $2.3M_{\odot }$ is obtained if the $M(R)$ slope is negative in the whole range of masses above $1M_{\odot }$, and a maximum mass above $2.4M_{\odot }$ requires the $M(R)$ slope to be positive in some range of masses. Constraints on the mass-radius curve of neutron stars will place strong constraints on microscopic models.

We show that a rigidly rotating, homogeneous ellipsoid of revolution threaded by a uniform, coaxial magnetic field is a possible figure of equilibrium. While the spheroidal shape is fully preserved, the rotation rate is modified. Accordingly, we extend the fundamental formula by Maclaurin. In contrast with the nonmagnetic case, prolate shapes are permitted, but there are critical states in the form of maximum elongations, depending on ionization fraction, ion/electron drift, magnetic field, and mass density. As checked from numerical simulations based on the self-consistent-field method, prolate states survive to gas compressibility. The relevance to interstellar clouds is outlined.

We study the merger of black hole-neutron star (BH-NS) binaries in numerical relativity, focusing on the properties of the remnant disk and the ejecta, varying the mass of compactness of the NS and the mass and spin of the BH. We find that within the precision of our numerical simulations, the remnant disk mass and ejecta mass normalized by the NS baryon mass (${\widehat{M}}_{\mathrm{rem}}$ and ${\widehat{M}}_{\mathrm{eje}}$, respectively), and the cutoff frequency $f_{\mathrm{cut}}$ normalized by the initial total gravitational mass of the system at infinite separation approximately agree among the models with the same NS compactness $C_{\mathrm{NS}}=M_{\mathrm{NS}}/R_{\mathrm{NS}}$, mass ratio $Q=M_{\mathrm{BH}}/M_{\mathrm{NS}}$, and dimensionless BH spin ${\chi }_{\mathrm{BH}}$ irrespective of the NS mass $M_{\mathrm{NS}}$ in the range of $1.092-1.691M_{\odot }$. This result shows that the merger outcome depends sensitively on $Q$, ${\chi }_{\mathrm{BH}}$, and $C_{\mathrm{NS}}$ but only weakly on $M_{\mathrm{NS}}$. This justifies the approach of studying the dependence of NS tidal disruptions on the NS compactness by fixing the NS mass but changing the EOS. We further perform simulations with massive NSs of $M_{\mathrm{NS}}=1.8M_{\odot }$, and compare our results of ${\widehat{M}}_{\mathrm{rem}}$ and ${\widehat{M}}_{\mathrm{eje}}$ with those given by existing fitting formulas to test their robustness for more compact NSs. We find that the fitting formulas obtained in the previous studies are accurate within the numerical errors assumed, while our results also suggest that further improvement is possible by systematically performing more precise numerical simulations.

Liquid argon is an excellent medium for detecting particles, given its yields and transport properties of light and charge. The technology of liquid argon time projection chambers has reached its full maturity after four decades of continuous developments and is, or will be, used in world class experiments for neutrino and dark matter searches. The collection of ionization charge in these detectors allows to perform a complete tridimensional reconstruction of the tracks of charged particles, calorimetric measurements, particle identification. This work proposes an innovative approach to the problem of charge recombination in liquid argon which moves from a microscopic model and is applied to the cases of low energy electrons, alpha particles, and nuclear recoils. It takes inspiration and expands the recombination models commonly used by the liquid argon community. The model is able to describe precisely several sets of experimental data available in the literature, over wide ranges of electric field strengths and kinetic energies and can be easily extended to other particles.

We study the effects of an oscillating axion field on the pressure between two metallic plates. We consider the situation where a magnetic field parallel to the plates is present and show that the electric field induced by the coupling of the axion to photons leads to resonances. When the boundary plates are perfect conductors, the resonances are infinitely thin whilst they are broadened when the conductivity of the boundary plates is taken into account. The resonances take place at the tower of distances close to $d_n=\frac{(2n+1)\pi }{m}$, where $m$ is the axion mass and have a finite width and height depending on the conductivity. The resulting resonant pressure on the plate depends on the induced polarization at the surface of the plates. We investigate the reach of future Casimir experiments in terms of the axion mass and the conductivity of the boundary plates. We find that for large enough conductivities, the axion-induced pressure could be larger than the quantum Casimir effect between the plates.

Spin effect on the pair production under circularly polarized fields is investigated. Significantly different from what momentum spirals caused by two counterrotating fields with a time delay, we find for the first time that the spirals can also be induced due to the particle spin effect even if in a single field. We further examine the bichromatic combinational fields. The inhomogeneous spiral structures can be observed in the momentum spectrum; in particular, the spiral not only does exist in two cases of spin, but also is about 2 orders of magnitude amplified compared with that in the single field. Meanwhile, the spin asymmetry degree on the momentum distributions is investigated, and it was found that the effect of spin flip exists with an increased time delay between two fields. The spin asymmetry degree on the number density can reach to 98% in certain conditions. These results indicate that the signatures of created particles, especially the spiral structures, are strongly associated with information pertaining to the laser field as well as the created particle spin, which can deepen the understanding of vacuum pair production.

We develop benchmarks for resonant discalar production in the generic complex singlet scalar extension of the Standard Model (SM) with no additional symmetries, which contains two new scalars. These benchmarks maximize discalar resonant production modes at future $pp$ colliders: $pp\to h_2\to h_1{h}_1$, $pp\to h_2\to h_1{h}_3$, and $pp\to h_2\to h_3{h}_3$, where $h_1$ is the observed SM-like Higgs boson and $h_{2,3}$ are new scalars. The decays $h_2\to h_1{h}_3$ and $h_2\to h_3{h}_3$ may be the only way to discover $h_3$, leading to a discovery of two new scalars at once. Current LHC and projected future collider (HL-LHC, FCC-$\mathrm{ee}+\mathrm{HL}$-LHC, $\mathrm{IL}\mathrm{C}500+\mathrm{HL}$-LHC) constraints on this model are used to produce benchmarks at the HL-LHC for $h_2$ masses between 250 GeV and 1 TeV and a future $pp$ collider (FCC-hh) for $h_2$ masses between 250 GeV and 12 TeV. We update the current LHC bounds on the singlet-Higgs boson mixing angle for these benchmarks. As the mass of $h_2$ approaches the multi-TeV region, certain limiting behaviors of the maximum rates are uncovered due to theoretical constraints on the parameters. These limits, which can be derived analytically, are $\mathrm{BR}(h_2\to h_1{h}_1)\to 0.25$, $\mathrm{BR}(h_2\to h_3{h}_3)\to 0.5$, and $\mathrm{BR}(h_2\to h_1{h}_3)\to 0$. It can also be shown that the maximum rates of $pp\to h_2\to h_1{h}_1$ and $pp\to h_2\to h_3{h}_3$ approach the same value. Hence, all three $h_2\to h_i{h}_j$ decays are promising discovery modes for $h_2$ masses at and below $\mathcal{O}(1\mathrm{TeV})$, while above $\mathcal{O}(1\mathrm{TeV})$ the decays $h_2\to h_1{h}_1$ and $h_2\to h_3{h}_3$ are more encouraging. We choose benchmark masses for $h_3$ to produce a large range of decay signatures including multi-$b$, multivector boson, and multi-SM-like Higgs production. As we will show, the behavior of the maximum rates leads to the surprising conclusion that in the multi-TeV region this model may be discovered in the Higgs quartet production mode via $h_2\to h_3{h}_3\to 4h_1$ decays before Higgs triple production is observed. The maximum di- and four Higgs production rates are similar in the multi-TeV range.

We interpret the recent excess in a rare decay of the Higgs boson, $H\to Z\gamma$, using a light axionlike particle (ALP) in the mass range 0.05–0.1 GeV. The dominant decay of such a light ALP is into a pair of collimated photons, whose decay is required to happen before reaching the ECAL detector, such that it mimics a single photon in the detector. It can explain the excess with a coupling $C_{aZH}^{\mathrm{eff}}/\mathrm{\Lambda }\sim 4\times {10}^{-5}{\mathrm{GeV}}^{-1}$, while the decay of the ALP before reaching the ECAL requires the diphoton coupling $C_{\gamma \gamma }^{\mathrm{eff}}/\mathrm{\Lambda }\ge 0.35{\mathrm{TeV}}^{-1}(0.1\mathrm{GeV}/m_a{)}^2$. A potential test would be the rare decay of the $Z$ boson $Z\to a{H}^{*}\to a(b\overline{b})$ at the Tera-$Z$ option of the future FCC and CEPC. However, it has a branching ratio of only $O({10}^{-12})$, and thus barely testable. The production cross section for $pp\to Z^{*}\to aH$ via the same coupling $C_{aZH}^{\mathrm{eff}}/\mathrm{\Lambda }$ at the LHC is too small for detection.

We propose a setup for the origin of dark matter based on spacetime with a warped extra dimension and three branes: the Planck brane, the TeV brane, at a (few) TeV scale ${\rho }_T$, and a dark brane, at a (sub-)GeV scale ${\rho }_1\lesssim 100\mathrm{GeV}\ll {\rho }_T$. The Standard Model (SM) is localized in the TeV brane, thus solving the Higgs hierarchy problem, while the dark matter $\chi$, a Dirac fermion with mass $m_{\chi }<{\rho }_1$, is localized in the dark brane. The radion, with mass $m_r<m_{\chi }$, interacts strongly [$\sim m_{\chi }/{\rho }_1\sim \mathcal{O}(1)$] with dark matter and very weakly ($\sim m_f{\rho }_1/{\rho }_T^2\ll 1$) with the Standard Model matter $f$. The generic conflict between the bounds on its detection signatures and its proper relic abundance is avoided as dark matter annihilation is $p$-wave suppressed. The former is determined by its very weak interactions with the SM and the latter by its much stronger annihilation into radions. Therefore, there is a vast range in the dark matter’s parameter space where the correct relic abundance is achieved consistently with the existing bounds. Moreover, for the dark brane with ${\rho }_1\lesssim 3\mathrm{GeV}$, a confinement/deconfinement first order phase transition, where the radion condensates, produces a stochastic gravitational wave background at the nanohertz frequencies, which can be identified with the signal detected by the Pulsar Timing Array (PTA) experiments. In the PTA window, for $0.15\lesssim m_{\chi }\lesssim 2\mathrm{GeV}$ the relic abundance is reproduced and all constraints are satisfied.

Because of the dense environment, neutron stars (NSs) can serve as an ideal laboratory for studying the interactions between dark matter (DM) and ordinary matter. In the process of DM capture, deep inelastic scattering may dominate over elastic scattering, especially for the DM with a large momentum transfer. In this work, we calculate DM-nucleon deep inelastic scattering via a vector mediator and estimate its contribution to the capture rate. Using the surface temperature of the NSs, we derive the exclusion limits for the DM-nucleon scattering cross section in the mass range $1\mathrm{GeV}<m_{\chi }<{10}^5\mathrm{GeV}$. We find the bounds for DM with the mass $\gtrsim 1\mathrm{GeV}$ can be changed several times after including the deep inelastic scattering contribution.