We consider $\mathcal{N}=1$ superconformal field theories in three dimensions possessing a conserved current multiplet ${\mathcal{F}}_{({\alpha }_1{\alpha }_2{\alpha }_3{\alpha }_4)}$, which we refer to as the superspin-2 current multiplet. At the component level it contains a conserved spin-2 current different from the energy-momentum tensor and a conserved fermionic higher-spin current of spin $5/2$. Using a superspace formulation, we calculate correlation functions involving $\mathcal{F}$, focusing particularly on the three-point function $⟨\mathcal{F}\mathcal{F}\mathcal{F}⟩$. After imposing the constraints arising from conservation equations and invariance under permutation of superspace points, we find that the parity-even and parity-odd sectors of this three-point function are each fixed up to a single coefficient. The presence of the parity-odd contribution is rather nontrivial, as there is an apparent tension between supersymmetry and the existence of parity-odd structures.

Schwarzschild black-hole interiors border on spacelike singularities representing classical information leaks. We show that local quantum physics is decoupled from these leaks due to dynamically generated boundaries, called Zeno borders. Beyond Zeno borders black-hole interiors become asymptotically silent, and quantum fields evolve freely toward the geodesic singularity with vanishing probability measure for populating the geodesic boundary. Thus Zeno borders represent a probabilistic completion of Schwarzschild black holes within the semiclassical framework.

In this work, taking the QED effect into account, we investigate the shadows of the Kerr black holes immersed in uniform magnetic fields through the numerical backward ray-tracing method. We introduce a dimensionless parameter $\mathrm{\Lambda }$ to characterize the strength of magnetic fields and study the influence of magnetic fields on the Kerr black hole shadows for various spins of the black holes and inclination angles of the observers. In particular, we find that the photon “hairs” appear near the left edge of the shadow in the presence of magnetic fields. The photon hairs may be served as a signature of the magnetic fields. We notice that the photon hairs become more evident when the strength of magnetic fields or the spin of the black hole becomes larger. In addition, we study the deformation of the shadows by bringing in quantitative parameters that can describe the position and shape of the shadow edge.

The fractional dark energy (FDE) model describes the accelerated expansion of the Universe through a nonrelativistic gas of particles with a noncanonical kinetic term. This term is proportional to the absolute value of the three-momentum to the power of $3w$, where $w$ is simply the dark energy equation of state parameter, and the corresponding energy leads to an energy density that mimics the cosmological constant. In this paper we expand the fractional dark energy model considering a nonzero chemical potential and we show that it may thermodynamically describe a phantom regime. The Planck constraints on the equation of state parameter put upper limits on the allowed value of the ratio of the chemical potential to the temperature. In the second part, we investigate the system of fractional dark energy particles with negative absolute temperatures (NAT). NAT are possible in quantum systems and in cosmology, if there exists an upper bound on the energy. This maximum energy is one ingredient of the FDE model and indicates a connection between FDE and NAT, if FDE is composed of fermions. In this scenario, the equation of state parameter is equal to minus one and, using cosmological observations, we find that the transition from positive to negative temperatures is allowed at any redshift larger than one.

In the next decades, the gravitational-wave (GW) standard siren observations and the neutral hydrogen 21-cm intensity mapping (IM) surveys, as two promising cosmological probes, will play an important role in precisely measuring cosmological parameters. In this work, we make a forecast for cosmological parameter estimation with the synergy between the GW standard siren observations and the 21-cm IM surveys. We choose the Einstein Telescope (ET) and the Taiji observatory as the representatives of the GW detection projects and choose the Square Kilometre Array (SKA) phase I mid-frequency array as the representative of the 21-cm IM experiments. In the simulation of the 21-cm IM data, we assume perfect foreground removal and calibration. We find that the synergy of the GW standard siren observations and the 21-cm IM survey could break the cosmological parameter degeneracies. The joint $\mathrm{ET}+\mathrm{Taiji}+\mathrm{SKA}$ data give $\sigma (H_0)=0.28\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$ in the $\mathrm{\Lambda }\mathrm{CDM}$ model, $\sigma (w)=0.028$ in the $w\mathrm{CDM}$ model, which are better than the results of $Planck+\mathrm{BAO}+\mathrm{SNe}$, and $\sigma (w_0)=0.077$ and $\sigma (w_a)=0.295$ in the CPL model, which are comparable with the results of $Planck+\mathrm{BAO}+\mathrm{SNe}$. In the $\mathrm{\Lambda }\mathrm{CDM}$ model, the constraint precision of $H_0$ and ${\mathrm{\Omega }}_{\mathrm{m}}$ is less than or rather close to 1%, indicating that the magnificent prospects for precision cosmology with these two promising cosmological probes are worth expecting.

We apply a recently developed formalism to study the evolution of a current-carrying string network under the simple but generic assumption of a linear equation of state. We demonstrate that the existence of a scaling solution with nontrivial current depends on the expansion rate of the Universe, the initial root-mean-square current on the string, and the available energy-loss mechanisms. We find that the fast expansion rate after radiation-matter equality will tend to rapidly dilute any preexisting current, and the network will evolve towards the standard Nambu-Goto scaling solution (provided there are no external current-generating mechanisms). During the radiation era, current growth is possible provided the initial conditions for the network generate a relatively large current and/or there is significant early string damping. The network can then achieve scaling with a stable nontrivial current, assuming large currents will be regulated by some leakage mechanism. The potential existence of current-carrying string networks in the radiation era, unlike the standard Nambu-Goto networks expected in the matter era, could have interesting phenomenological consequences.

We performed a detailed analysis of the detectability of a wide range of gravitational waves derived from core-collapse supernova simulations using gravitational-wave detector noise scaled to the sensitivity of the upcoming fourth and fifth observing runs of the Advanced LIGO, Advanced Virgo, and KAGRA. We use the coherent WaveBurst algorithm, which was used in the previous observing runs to search for gravitational waves from core-collapse supernovae. As coherent WaveBurst makes minimal assumptions on the morphology of a gravitational-wave signal, it can play an important role in the first detection of gravitational waves from an event in the Milky Way. We predict that signals from neutrino-driven explosions could be detected up to an average distance of 10 kpc, and distances of over 100 kpc can be reached for explosions of rapidly-rotating progenitor stars. An estimated minimum signal-to-noise ratio of 10–25 is needed for the signals to be detected. We quantify the accuracy of the waveforms reconstructed with coherent WaveBurst and we determine that the most challenging signals to reconstruct are those produced in long-duration neutrino-driven explosions, and models that form black holes a few seconds after the core bounce.

After the detection of gravitational waves from compact binary coalescences, the search for transient gravitational-wave signals with less well-defined waveforms for which matched filtering is not well suited is one of the frontiers for gravitational-wave astronomy. Broadly classified into “short” $\lesssim 1\mathrm{s}$ and “long” $\gtrsim 1\mathrm{s}$ duration signals, these signals are expected from a variety of astrophysical processes, including non-axisymmetric deformations in magnetars or eccentric binary black hole coalescences. In this work, we present a search for long-duration gravitational-wave transients from Advanced LIGO and Advanced Virgo’s third observing run from April 2019 to March 2020. For this search, we use minimal assumptions for the sky location, event time, waveform morphology, and duration of the source. The search covers the range of 2–500 s in duration and a frequency band of 24–2048 Hz. We find no significant triggers within this parameter space; we report sensitivity limits on the signal strength of gravitational waves characterized by the root-sum-square amplitude $h_{\mathrm{rss}}$ as a function of waveform morphology. These $h_{\mathrm{rss}}$ limits improve upon the results from the second observing run by an average factor of 1.8.

I introduce a modification of continuous matrix product states (CMPS) that makes them adapted to relativistic quantum field theories (QFT). These relativistic CMPS can be used to solve genuine ($1+1$)-dimensional QFT without UV cutoff and directly in the thermodynamic limit. The main idea is to work directly in the basis that diagonalizes the free part of the model considered, which allows one to fit its short distance behavior exactly. This makes computations slightly less trivial than with standard CMPS. However, they remain feasible, and I present all the steps needed for the optimization. The asymptotic cost as a function of the bond dimension remains the same as for standard CMPS. I illustrate the method on the self-interacting scalar field, also known as the ${\varphi }_2^4$ model. Aside from providing unequaled precision in the continuum, the numerical results obtained are truly variational, and thus provide rigorous energy upper bounds.

Nambu-Goldstone bosons, or axions, may be ubiquitous. Some of the axions may have small masses and thus serve as mediators of long-range forces. In this paper, we study the force mediated by an extremely light axion, $\varphi$, between the visible sector and the dark sector, where dark matter lives. Since nature does not preserve the $CP$ symmetry, the coupling between dark matter and $\varphi$ is generically $CP$ violating. In this case, the induced force is extremely long range and behaves as an effective magnetic field. If the force acts on electrons or nucleons, the spins of them on Earth precess around a fixed direction toward the Galactic Center. This provides an experimental opportunity for $\varphi$ with mass, $m_{\varphi }$, and decay constant, $f_{\varphi }$, satisfying $m_{\varphi }\lesssim {10}^{-25}\mathrm{eV}$, $f_{\varphi }\lesssim {10}^{14}\mathrm{GeV}$ if the daily modulation of the effective magnetic field signals in magnetometers is measured by using the coherent averaging method. The effective magnetic field induced by an axionic compact object, such as an axion domain wall, is also discussed.

We study the effect of interference on the lepton number violating (LNV) and lepton number conserving (LNC) three-body meson decays $M_1^{+}\to l_i^{+}{l}_j^{\pm }{\pi }^{\mp }$ that arise in a TeV-scale left-right symmetric model (LRSM) with degenerate or nearly degenerate right-handed (RH) neutrinos. The LRSM contains three RH neutrinos and a RH gauge boson. The RH neutrinos with masses in the range of $M_N\sim$ (MeV–few GeV) can give resonant enhancement in the semileptonic LNV and LNC meson decays. In the case where only one RH neutrino contributes to these decays, the predicted new physics branching ratios of semileptonic LNV and LNC meson decays $M_1^{+}\to l_i^{+}{l}_j^{+}{\pi }^{-}$ and $M_1^{+}\to l_i^{+}{l}_j^{-}{\pi }^{+}$ are equal. We find that with at least two RH neutrinos contributing to the process, the LNV and LNC decay rates can differ. Depending on the neutrino mixing angles and $CP$-violating phases, the branching ratios of LNV and LNC decay channels mediated by the heavy neutrinos can be either enhanced or suppressed, and the ratio of these two rates can differ from unity.

The recent Fermilab measurement of the muon anomalous magnetic moment yields $4.2\sigma$ deviations from the SM prediction when combined with the BNL E821 experiment results. In the type-X two-Higgs-doublet model, we study the consequence of imposing the observed muon $g-2$, along with the constraints from theoretical stabilities, electroweak oblique parameters, Higgs precision data, and direct searches. For a comprehensive study, we scan the whole parameter space in two scenarios, the normal scenario where $h_{\mathrm{SM}}=h$ and the inverted scenario where $h_{\mathrm{SM}}=H$, where $h$ ($H$) is the light (heavy) $CP$-even Higgs boson. We found that large $\tan \beta$ (above 100) and light pseudoscalar mass $M_A$ are required to explain the muon $g-2$ anomaly. This breaks the theoretical stability unless the scalar masses satisfy $M_A^2\simeq M_{H^{\pm }}^2\simeq m_{12}^2\tan \beta \approx M_{H/h}^2$. The direct search bounds at the LEP and LHC exclude the light $A$ window with $M_A\lesssim 62.5\mathrm{GeV}$. We also show that the observed electron anomalous magnetic moment is consistent with the model prediction, but the lepton flavor universality data in the $\tau$ and $Z$ decays are not. For a separate exploration of the model, we propose the golden mode $pp\to Ah/AH\to 4\tau$ at the HL-LHC.

We discuss the naive lattice fermion without the issue of doublers. A local lattice massless fermion action with chiral symmetry and Hermiticity cannot avoid the doubling problem from the Nielsen-Ninomiya theorem. Here we adopt the forward finite-difference deforming the ${\gamma }_5$-Hermiticity but preserving the continuum chiral symmetry. The lattice momentum is not Hermitian without the continuum limit now. We demonstrate that there is no doubling issue from an exact solution. The propagator only has one pole in the first-order accuracy. Therefore, it is hard to know the avoiding due to the non-Hermiticity. For the second-order, the lattice propagator has two poles as before. This case also does not suffer from the doubling problem. Hence separating the forward derivative from the backward one evades the doublers under the field theory limit. Simultaneously, it is equivalent to breaking the Hermiticity. In the end, we discuss the topological charge and also demonstrate the numerical implementation of the hybrid Monte Carlo.

Analyzing $(448.1\pm 2.9)\times {10}^6\psi (3686)$ events collected with the BESIII detector at the BEPCII collider, the $\psi (3686)\to \omega K_S^0{K}_S^0$ decay is observed for the first time. The branching fraction for this decay is determined to be ${\mathcal{B}}_{\psi (3686)\to \omega K_S^0{K}_S^0}=(7.04\pm 0.39\pm 0.36)\times {10}^{-5}$, where the first uncertainty is statistical and the second is systematic.

Formulations of magnetic monopoles in a Hilbert-space formulation of quantum mechanics require Dirac’s quantization condition of magnetic charge, which implies a large value that can easily be ruled out for elementary particles by standard atomic spectroscopy. However, an algebraic formulation of nonassociative quantum mechanics is mathematically consistent with fractional magnetic charges of small values. Here, spectral properties in nonassociative quantum mechanics are derived and applied to the ground state of hydrogen with a magnetically charged nucleus. The resulting energy leads to new strong upper bounds for the magnetic charge of various elementary particles that can appear as the nucleus of hydrogenlike atoms, such as the muon or the antiproton.

On a class of four-dimensional Lifshitz spacetimes with critical exponent $z=2$, including a hyperbolic and a spherical Lifshitz topological black hole, we consider a real Klein-Gordon field. Using a mode decomposition, we split the equation of motion into a radial and into an angular component. As first step, we discuss under which conditions on the underlying parameters we can impose to the radial equation boundary conditions of Robin type and whether bound state solutions do occur. Subsequently, we show that, whenever bound states are absent, one can associate to each admissible boundary condition a ground and a KMS state whose associated two-point correlation function is of local Hadamard form.

We study, in the imaginary time formalism, the relation between loops and on-shell forward scattering tree amplitudes in thermal field theories. This allows for an efficient evaluation, at all temperatures, of Green’s functions with causal retarded boundary conditions. We present an application of this relation in quantum gravity coupled to scalar matter fields. We show that at one or two loops, involving planar diagrams, the 1PI retarded thermal Green’s functions may respectively be expressed in terms of connected forward scattering tree amplitudes of one or two on-shell particles.

Recent models formulated by Kafri, Taylor, and Milburn and by Tilloy and Diosi describe the gravitational interaction through a continuous measurement and feedback protocol. In such a way, although gravity is ultimately treated as classical, they can reconstruct the proper quantum gravitational interaction at the level of the master equation for the statistical operator. Following this procedure, the price to pay is the presence of decoherence effects leading to an asymptotic energy divergence. One does not expect the latter in isolated systems. Here, we propose a dissipative generalization of these models. We show that, in these generalizations, in the long time limit, the system thermalizes to an effective finite temperature.

We study models of nonminimally coupled relativistic fluid and the $k$-essence scalar field in the background of a flat Friedmann-Lemaitre-Robertson-Walker universe. The nonminimal coupling term is introduced in the Lagrangian level. We employ the variational approach with respect to independent variables that produce modified $k$-essence field equations and the Friedmann equations. We have analyzed the coupled field-fluid framework explicitly using the dynamical system technique considering two different models based on inverse power-law potential. After examining these models it is seen that both models are capable of producing accelerating attractor solutions satisfying adiabatic sound speed conditions.

In this work, we elaborate on the finite action in the framework of Hořava-Lifshitz gravity. Assuming the finite action principle, we show that the beginning of the Universe is flat and homogeneous. Depending on the version of the theory, different cosmological scenarios are possible. Furthermore, we show that the Hořava-Lifshitz gravity action selects only the regular black-hole spacetimes since the singular black holes possess infinite action. We also comment on the possibility of traversable wormholes in theories with higher-curvature invariants. The possible cosmological solutions in Hořava-Lifshitz and quadratic gravity are similar, proving that the finite action principle is not model sensitive.