We demonstrate the power of a first principle-based and practicable method that allows for the perturbative computation of reduced density matrix elements of an open quantum system without making use of any master equations. The approach is based on techniques from nonequilibrium quantum field theory such as thermo field dynamics, the Schwinger-Keldsyh formalism, and the Feynman-Vernon influence functional. It does not require the Markov approximation and is essentially a Lehmann-Szymanzik-Zimmermann-like reduction. To illustrate this method, we consider a real scalar field as an open quantum system interacting with an environment comprising another real scalar field. We give a general formula that allows for the perturbative computation of density matrix elements for any number of particles in a momentum basis. Finally, we consider a simple toy model and use this formula to obtain expressions for some of the system’s reduced density matrix elements.

In the search for axion dark matter, the cavity-based haloscope offers the most sensitive approach to the theoretically interesting models in the microwave region. However, experimental searches have been limited to relatively low masses up to a few tens of $\mathrm{\mu }\mathrm{eV}$, benefiting from large detection volumes and high-quality factors for a given experimental setup. We propose a new cavity design suitable for axion searches in higher mass regions with enhanced performance. The design features a periodic arrangement of dielectric material in a conventional conducting cavity where the resonant frequency is determined by the interspace. This photonic crystal haloscope can make full use of a given volume even at high frequencies while substantially improving the cavity quality factor. An auxetic structure is considered to deploy the array for two-dimensional frequency tuning. We present the characteristics of this haloscope design and demonstrate its feasibility for high-mass axion searches.

Recent experimental results in $B$ physics from Belle, BABAR, and LHCb suggest new physics (NP) in the weak $b\to c$ charged-current processes. Here we focus specifically on the decay modes ${\overline{B}}^0\to D^{*+}{\ell }^{-}\overline{\nu }$ with $\ell =e$ and $\mu$. The world averages of the ratios $R_D$ and $R_D^{*}$ currently differ from the Standard Model (SM) predictions by $3.4\sigma$ while recently a new anomaly has been observed in the forward-backward asymmetry measurement, $A_{\mathrm{FB}}$, in ${\overline{B}}^0\to D^{*+}{\mu }^{-}\overline{\nu }$ decay. It is found that $\mathrm{\Delta }{A}_{\mathrm{FB}}=A_{\mathrm{FB}}(B\to D^{*}\mu \nu )-A_{\mathrm{FB}}(B\to D^{*}e\nu )$ is around $4.1\sigma$ away from the SM prediction in an analysis of 2019 Belle data. In this work we explore possible solutions to the $\mathrm{\Delta }{A}_{\mathrm{FB}}$ anomaly and point out correlated NP signals in other angular observables. These correlations between angular observables must be present in the case of beyond the Standard Model physics. We stress the importance of $\mathrm{\Delta }$ type observables that are obtained by taking the difference of the observable for the muon and the electron mode. These quantities cancel form-factor uncertainties in the SM and allow for clean tests of NP. These intriguing results also suggest an urgent need for improved simulation and analysis techniques in ${\overline{B}}^0\to D^{*+}{\ell }^{-}\overline{\nu }$ decays. Here we also describe a new Monte Carlo event generator tool based on EVTGEN that we developed to allow simulation of the NP signatures in ${\overline{B}}^0\to D^{*+}{\ell }^{-}\nu$, which arise due to the interference between the SM and NP amplitudes. We then discuss prospects for improved observables sensitive to NP couplings with 1, 5, 50, and $250{\mathrm{ab}}^{-1}$ of Belle II data, which seem to be ideally suited for this class of measurements.

I discretize axion string configuration coupled to a Dirac fermion, which in the continuum binds a massless chiral fermion in its core when the winding is one. I show that such a configuration can host one or more chiral fermions when regulated on the lattice. To realize these chiral fermions I introduce Wilson-like terms similar to the Wilson term used in lattice domain wall fermions. The number of chiral fermions on the string jumps as the Wilson-like parameter is varied with respect to the other mass scales in the problem. A one-loop Feynman diagram is used to demonstrate how anomaly inflow works in this lattice regularized theory.

We study the Roberge-Weiss phase transition numerically. The phase transition is associated with the discontinuities in the quark-number density at specific values of imaginary quark chemical potential. We parametrize the quark-number density ${\rho }_q$ by the polynomial fit function to compute the canonical partition functions. We demonstrate that this approach provides a good framework for analyzing lattice QCD data at finite density and a high temperature. We show numerically that, at high temperature, the Lee-Yang zeros lie on the negative real semiaxis provided that the high-quark-number contributions to the grand canonical partition function are taken into account. These Lee-Yang zeros have nonzero linear density, which signals the Roberge-Weiss phase transition. We demonstrate that this density agrees with the quark-number density discontinuity at the transition line.

We consider the time-dependent analysis of rare $B_d$ and $B_s$ decays mediated by $b\to s\nu \overline{\nu }$ transitions. The inclusion of time evolution allows us to construct novel observables with specific sensitivity to $CP$-odd phases in these processes. The sensitivity to $CP$ violation of corresponding time-integrated measurements in the presence of flavor tagging is also explored. We provide precise predictions for these observables in the Standard Model and explore their sensitivity to new $CP$-violating new physics contributions at present and planned future $B$-physics experiments. As such, these observables provide unique probes of $CP$ violation in $b\to s\nu \overline{\nu }$ transitions.

We study $B\to \pi \pi$ decay with a modified perturbative QCD approach. The branching ratios and $CP$ violation are calculated with the transverse momenta of partons considered. Sudakov factor associated with each meson is included to suppress soft contribution in QCD. With the wave function of $B$ meson obtained in QCD-inspired relativistic potential model being used, the suppression of Sudakov factor to the soft contribution is not effective enough. Soft scale cutoff and soft form factors of $B\pi$ transition and $\pi \pi$ production have to be introduced. The main next-to-leading-order contributions of vertex correction, the quark-loop, and magnetic penguin are included. To solve the long-standing puzzle in $B\to \pi \pi$ decay, that is the theoretical prediction of the branching ratio of $B^0\to {\pi }^0{\pi }^0$ being seriously smaller than experimental data, color-octet matrix element which is of long-distance dynamics is introduced. With parameters taken with reasonable values, all the branching ratios and $CP$ violation are well consistent with experimental data.

The search for scale-invariant random geometries is central to the asymptotic safety hypothesis for the Euclidean path integral in quantum gravity. In an attempt to uncover new universality classes of scale-invariant random geometries that go beyond surface topology, we explore a generalization of the mating of trees approach introduced by Duplantier, Miller, and Sheffield. The latter provides an encoding of Liouville quantum gravity on the 2-sphere decorated by a certain random space-filling curve in terms of a two-dimensional correlated Brownian motion, that can be viewed as describing a pair of random trees. The random geometry of Liouville quantum gravity can be conveniently studied and simulated numerically by discretizing the mating of trees using the mated-CRT maps of Gwynne, Miller, and Sheffield. Considering higher-dimensional correlated Brownian motions, one is naturally led to a sequence of nonplanar random graphs generalizing the mated-CRT maps that may belong to new universality classes of scale-invariant random geometries. We develop a numerical method to efficiently simulate these random graphs and explore their possible scaling limits through distance measurements, allowing us in particular to estimate Hausdorff dimensions in the two- and three-dimensional setting. In the two-dimensional case these estimates accurately reproduce previous known analytic and numerical results, while in the three-dimensional case they provide a first window on a potential three-parameter family of new scale-invariant random geometries.

In this paper, we have analyzed the information paradox and its resolution using the island proposal in Schwarzschild de-Sitter black hole spacetime. First, we study the information paradox for the black hole patch by treating de-Sitter patch on both sides as a frozen background (by inserting thermal opaque membranes) and then carry out a similar study for de-Sitter patch. In both cases, when there is no island surface, the entanglement entropy has the linear time dependence as usual, whereas in the presence of an island surface, entanglement entropy becomes constant (equal to twice of thermal entropy of black hole/de-Sitter patch). Therefore, we obtain the Page curves for the black hole and de-Sitter patches consistent with the unitary evolution of black holes. In our case, we have found that the black hole island is located inside the black hole event horizon in contrast to the universal result for eternal black holes, and the cosmological island is also located inside cosmological event horizon. Further, we have studied the “effect of temperature” on Page curves and found that Page curves appear at late times for low-temperature black hole/de-Sitter patch and exhibit the opposite behavior for high-temperature. This implies that “dominance of islands” and “information recovery” takes more time for low-temperature black hole/de-Sitter patch in contrast to high-temperature black hole/de-Sitter patch. We also comment on the challenges of studying the information paradox in SdS spacetime without the thermal opaque membranes.

We compute to high post-Newtonian accuracy the 4-momentum (linear momentum and energy), radiated as gravitational waves in a two-body system undergoing gravitational scattering. We include, for the first time, all the relevant time-asymmetric effects that arise when consistently going three post-Newtonian orders beyond the leading post-Newtonian order. We find that the inclusion of time-asymmetric radiative effects (both in tails and in the radiation-reacted hyperbolic motion) is crucial to ensure the mass polynomiality of the post-Minkowskian expansion ($G$ expansion) of the radiated 4-momentum. Imposing the mass polynomiality of the corresponding individual impulses determines the conservativelike radiative contributions at the fourth post-Minkowskian order and strongly constrains them at the fifth post-Minkowskian order.

The bumblebee gravity model is a vector-tensor theory of gravitation where the vector field nonminimally couples to the Ricci tensor. By investigating the vacuum field equations with spherical symmetry, we find two families of black-hole (BH) solutions in this model: one has a vanishing radial component of the vector field and the other has a vanishing radial component of the Ricci tensor. When the coupling between the vector field and the Ricci tensor is set to zero, the first family becomes the Reissner-Nordström solution while the second family degenerates to the Schwarzschild solution with the vector field being zero. General numerical solutions in both families are obtained for nonzero coupling between the vector field and the Ricci tensor. Besides BH solutions, we also reveal the existence of solutions that have a nonvanishing $tt$-component of the metric on the supposed event horizon where the $rr$-component of the metric diverges while the curvature scalars are finite. These solutions are not supported by existing observations but present certain properties that are of academic interests. We conclude the study by putting the BH solutions into tests against the Solar-System observations and the images of supermassive BHs.

We develop a Hamiltonian description of the “Carroll” (Levy Leblond-Sen Gupta) limit of gravity theory in the first-order formalism. Through a constraint analysis, the number of local degrees of freedom are shown to be two in this singular limit. The Hamiltonian constraint in this (“magnetic”) limit depends only on the densitized triad fields and their space derivatives. We also provide a scaling prescription within the Hilbert-Palatini theory to obtain the first-order analogue of the “electric” limit of canonical metric gravity. The simplicity of both these limiting Hamiltonian forms in these variables make them interesting candidates for quantization.

Cosmological perturbation theory is known to converge poorly for predicting the spherical collapse and void evolution of collisionless matter. Using the exact parametric solution as a testing ground, we develop two asymptotic methods in spherical symmetry that resolve the gravitational evolution to much higher accuracy than Lagrangian perturbation theory (LPT), which is the current gold standard in the literature. One of the methods selects a stable fixed-point solution of the renormalization-group flow equation, thereby predicting already at the leading order the critical exponent of the phase transition to collapsed structures. The other method completes the truncated LPT series far into the UV regime, by adding a nonanalytic term that captures the critical nature of the gravitational collapse. We find that the UV method most accurately resolves the evolution of the nonlinear density as well as its one-point probability distribution function. Similarly accurate predictions are achieved with the renormalization-group method, especially when paired with Padé approximants. Further, our results yield new, very accurate, formulas to relate linear and nonlinear density contrasts. Finally, we chart possible ways on how to adapt our methods to the case of cosmological random field initial conditions.

We study the effect of baryons on the cosmic web—halos, filaments, walls, and voids. To do so, we apply a modified version of NEXUS, a cosmic web morphological analysis algorithm, to the IllustrisTNG simulations. We find that halos lose more than 10% of their mass due to baryons, mostly to filaments and a small portion to walls and voids. However, the mass transfer does not significantly shift the boundaries of structures, leaving the volume fractions of the cosmic structures largely unaffected. We quantify the effects of baryonic feedback on the power spectrum and the probability density function of the density field for individual cosmic structures. For the power spectrum, most suppression due to feedback can be accounted for by including $M\ge {10}^{12}{M}_{\odot }/h$ halos, without considering other cosmic structures. However, when examining the probability density function of the density field, we find nearly 100% suppression of the emptiest regions and 10%-level effects (boost or suppression) in the remaining regions of filaments, walls, and voids. Our results indicate the importance of modeling the effects of baryons in the whole cosmic web, not just halos, for cosmological analysis beyond two-point statistics or field-based inferences.

Recent radio-frequency probes, with the ATCA and ASKAP telescopes, have proven themselves to be at the forefront of placing indirect limits on the properties of dark matter. The latter being able to substantially exceed the constraining power of Fermi-LAT data. However, these observations were based only on dwarf galaxies, where magnetic field uncertainties are large. Here we reexamine the case for galaxy clusters, often ignored due to substantial diffuse radio backgrounds, by considering the extrapolation of known cluster surface brightness profiles down to scales observable with MeerKAT. Despite large baryonic backgrounds, we find that clusters can be competitive with dwarf galaxies. Extrapolated Coma data being able to rule out weakly interacting massive particles of mass $<700\mathrm{GeV}$ annihilating via $b$-quarks. This is while having lesser uncertainties surrounding the magnetic field and diffusive environment. Such compelling results are possible due to a clash between the inner shape of the dark matter halo and the flat inner profile of radio halos which is most pronounced for Navarro-Frenk-White-like Einasto profiles, the presence of which having some supporting evidence in the literature.

We derive the approximate “analytic-kludge” waveforms for the inspiral of a charged stellar-mass compact object (CO) into a charged massive Kerr-Newman black hole. The modifications of the inspiral orbit due to the charges in this system can be attributed to three sources: the electric force between the CO and the massive black holes (MBH), the energy flow of the dipole electromagnetic radiation, and the deformation of the metric caused by the charge of the MBH. All these are encoded explicitly in the fundamental frequencies of the orbits, which are calculated analytically in the weak-field regime. By calculating the mismatch between the waveforms for charged and neutral extreme-mass-ratio inspirals systems with respect to space-borne detectors TianQin and LISA, we show that tiny charges in the system can produce distinct imprints on the waveforms. Finally, we perform parameter estimation for the charges using the Fisher information matrix method and find that the precision can reach the level of ${10}^{-5}$ in suitable scenarios. We also study the effects of charges on the parameter estimation of charge, where the effects from the charge of the MBH can be well explained by its effects on the cutoff of the inspiral.

We report Earth-scale distance magnetic correlations from lightning strokes in the frequency range 1–1000 Hz at several distances ranging from 1100 km to 9000 km. Noise sources which are correlated on Earth-scale distances can affect future searches for gravitational-wave signals with ground-based gravitational-wave interferometric detectors. We consider the impact of correlations from magnetic field fluctuations on gravitational-wave searches due to Schumann resonances ($<50\mathrm{Hz}$) as well as higher frequencies ($>100\mathrm{Hz}$). We demonstrate that individual lightning strokes are a likely source for the observed correlations in the magnetic field fluctuations at gravitational-wave observatories and discuss some of their characteristics. Furthermore, we predict their impact on searches for an isotropic gravitational-wave background, as well as for searches looking for short-duration transient gravitational waves, both unmodeled signals (bursts) as well as modeled signals (compact binary coalescence). Whereas the recent third observing run by LIGO and Virgo was free of an impact from correlated magnetic field fluctuations, future runs could be affected. In particular, third-generation detectors may be highly susceptible to these correlated magnetic transients in the various searches as well as parameter estimation. We suggest that future detector design should consider reducing lightning coupling by, for example, reducing the lightning-induced beam tube currents that pass through sensitive magnetic coupling regions in current detectors. We also suggest that the diurnal and seasonal variation in lightning activity may be useful in discriminating between detector correlations that are produced by gravitational waves and those produced by lightning.

We study quantum fluctuations in the light-cone metric of the 4D Einstein-Hilbert action via dimensional reduction to Jackiw-Teitelboim (JT) gravity. In particular, we show that, in Einstein gravity, the causal development of a region in flat Minkowski spacetime, near a horizon defined by light sheets, can be described by an effective two-dimensional dilaton theory. This enables us to make use of known solutions of the JT action, where the spacetime position of a horizon has quantum uncertainty due to metric fluctuations. This quantum uncertainty can be then directly related to the original 4D light-cone coordinates, allowing us to compute the uncertainty in the time of a photon to travel from tip-to-tip of a causal diamond in flat 4D Minkowski space. We find that both Planck and infrared scales (with the latter set by the size of the causal diamond) enter the uncertainty in photon travel time, such that the quantum fluctuation in the arrival time may be observably large.

The recoil threshold of direct detection (DD) experiments limits the mass range of dark matter (DM) particles that can be detected, with most DD experiments being blind to sub-MeV DM particles. However, these light DM particles can be boosted to very high energies via collisions with energetic cosmic ray electrons. This allows dark matter particles to induce detectable recoil in the target of direct detection experiments. We derive constraints on a scattering cross section of DM and an electron, using XENONnT and Super-Kamiokande data. Vector and scalar mediators are considered in the heavy and light regimes. We discuss the importance of including energy-dependent cross sections (due to the specific Lorentz structure of the vertex) in our analysis and show that the bounds can be significantly different than the results obtained assuming a constant energy-independent cross section, often assumed in the literature for simplicity. Our bounds are also compared with other astrophysical and cosmological constraints.

Recently, the definitions of the Kimber-Martin-Ryskin-Watt (KMRW) unintegrated parton densities (UPDFs) have been discussed by several groups. In the first part of this manuscript, we remind the reader about the issues encountered with these definitions and discuss the proposed solutions. In our opinion, none of these solutions is fully satisfactory. We observe that these issues seem to be related to the normalization condition where the UPDFs are related to the collinear PDFs by an integration over transverse momentum cut off by the factorization scale. Then, we build a modified version of the angular-ordering KMRW UPDFs, obeying the normalization condition with the transverse momentum integrated up to infinity and show that the usual issues are absent.