The chiral magnetic effect (CME) has been investigated as a new transport phenomenon in condensed matter. Such an effect appears in systems with chiral fermions and involves an electric current generated by a magnetic field by means of an “exotic” magnetic conductivity. This effect can also be connected with extensions of the usual Ohm’s law either in magnetohydrodynamics or in Lorentz-violating scenarios. In this work, we study the classical propagation of electromagnetic waves in isotropic dispersive matter subject to a generalized Ohm’s law. The latter involves currents linear in the magnetic field and implies scenarios inducing parity violation. We pay special attention to the case of a vanishing electric conductivity. For a diagonal magnetic conductivity, which includes the CME, the refractive index is modified such that it leads to birefringence. For a nondiagonal magnetic conductivity, modified refractive indices exhibiting imaginary parts occur ascribing a conducting behavior to a usual dielectric medium. Our findings provide new insights into typical material properties associated with a magnetic conductivity.

Motivated by the understanding of holography as realized in tensor networks, we develop a bulk procedure that can be interpreted as generating a sequence of coarse-grained holographic states. The coarse-graining procedure involves identifying degrees of freedom entangled at short distances and disentangling them. This is manifested in the bulk by a flow equation that generates a codimension-1 object, which we refer to as the holographic slice. We generalize the earlier classical construction to include bulk quantum corrections, which naturally involves the generalized entropy as a measure of the number of relevant boundary degrees of freedom. The semiclassical coarse graining results in a flow that approaches quantum extremal surfaces such as entanglement islands that have appeared in discussions of the black hole information paradox. We also discuss the relation of the present picture to the view that the holographic dictionary works as quantum error correction.

In this paper we study the observational constraints that can be imposed on the coupling parameter $\widehat{\alpha }$ of the regularized version of the four-dimensional Einstein-Gauss-Bonnet theory of gravity. We use the scalar-tensor field equations of this theory to perform a thorough investigation of its slow-motion and weak-field limit and apply our results to observations of a wide array of physical systems that admit such a description. We find that the Laser Geometric Environmental Observation Survey satellites are the most constraining, requiring $|\widehat{\alpha }|\lesssim {10}^{10}{\mathrm{m}}^2$. This constraint suggests that the possibility of large deviations from general relativity is small in all systems except the very early Universe ($t<{10}^{-3}\mathrm{s}$) or the immediate vicinity of stellar-mass black holes ($M\lesssim 100M_{\odot }$). We then consider constraints that can be imposed on this theory from cosmology, black hole systems, and tabletop experiments. It is found that early Universe inflation prohibits all but the smallest negative values of $\widehat{\alpha }$, while observations of binary black hole systems are likely to offer the tightest constraints on positive values, leading to overall bounds $0\lesssim \widehat{\alpha }\lesssim {10}^8{\mathrm{m}}^2$.

We propose a class of theories that can limit scalars constructed from the extrinsic curvature. Applied to cosmology, this framework allows us to control not only the Hubble parameter but also anisotropies without the problem of Ostrogradsky ghost, which is in sharp contrast to the case of limiting spacetime curvature scalars. Our theory can be viewed as a generalization of mimetic and cuscuton theories (thus clarifying their relation), which are known to possess a structure that limits only the Hubble parameter on homogeneous and isotropic backgrounds. As an application of our framework, we construct a model where both anisotropies and the Hubble parameter are kept finite at any stage in the evolution of the universe in the diagonal Bianchi type I setup. The universe starts from a constant-anisotropy phase and recovers Einstein gravity at low energies. We also show that the cosmological solution is stable against a wide class of perturbation wave numbers, though instabilities may remain for arbitrary initial conditions.

We consider the dynamics of particles, particularly focusing on circular orbits in the higher-dimensional Majumdar-Papapetrou (MP) spacetimes with two equal mass black holes. It is widely known that in the 5D Schwarzschild-Tangherlini and Myers-Perry backgrounds, there are no stable circular orbits. In contrast, we show that in the 5D MP background, stable circular orbits can always exist when the separation of two black holes is large enough. More precisely, for a large separation, stable circular orbits exist from the vicinity of horizons to infinity; for a medium one, they appear only in a certain finite region bounded by the innermost stable circular orbit and the outermost stable circular orbit outside the horizons; for a small one, they do not appear at all. Moreover, we show that in MP spacetimes in more than 5D, they do not exist for any separations.

The ten-parameter, quadratic Poincaré gauge theory of gravity is a plausible alternative to general relativity. We show that the rich background cosmology of the gauge theory is described by a noncanonical biscalar-tensor theory in the Jordan frame: the metrical analogue. This provides a unified framework for future investigation by the broader community. For many parameter choices, the noncanonical term reduces to a Cuscuton field of the form $\sqrt{|X^{\varphi \varphi }|}$. The Einstein–Cartan–Kibble–Sciama theory maps to a pure quadratic cuscuton, whereas the teleparallel theory maps to the Einstein–Hilbert Lagrangian. We apply the metrical analogue to novel unitary and power-counting-renormalizable cases of Poincaré gauge theory. These theories support the concordance $\mathrm{\Lambda }\mathrm{CDM}$ background cosmology up to an optional, effective dark radiation component, we explain this behavior in terms of a stalled cuscuton. We also obtain two dark energy solutions from one of these cases: accelerated expansion from a negative bare cosmological constant whose magnitude is screened, and emergent dark energy to replace vanishing bare cosmological constant in $\mathrm{\Lambda }\mathrm{CDM}$.

The gauge dependence of the scalar induced gravitational waves (SIGWs) generated at the second order imposes a challenge to the discussion of the secondary gravitational waves generated by scalar perturbations. We provide a general formula that is valid in any gauge for the calculation of SIGWs and the relationship for SIGWs calculated in various gauges under the coordinate transformation. The formula relating SIGWs in the Newtonian gauge to other gauges is used to calculate SIGWs in six different gauges. We find that the Newtonian gauge, the uniform curvature gauge, the synchronous gauge, and the uniform expansion gauge yield the same result for the energy density of SIGWs. We also identify and eliminate the pure gauge modes that existed in the synchronous gauge. In the total matter gauge and the comoving orthogonal gauge, the energy density of SIGWs increases as ${\eta }^2$. While in the uniform density gauge, the energy density of SIGWs increases as ${\eta }^6$.

The recent EDGES measurements of the global 21-cm signal from the cosmic dawn suggest that the kinetic temperature of the intergalactic medium (IGM) might be significantly lower compared to its expected value. The colder IGM directly affects the hydrogen recombination of the universe during the cosmic dawn and dark ages by enhancing the rate of recombinations. Here, we study and quantify, the impact of the colder IGM scenario on the recombination history of the universe in the context of DM-baryonic interaction model which is widely used to explain the depth of the EDGES 21-cm signal. We find that, in general, the hydrogen ionisation fraction gets suppressed during the dark ages and cosmic dawn and the suppression gradually increases at lower redshifts until x-ray heating turns on. However, accurate estimation of the ionization fraction requires knowledge of the entire thermal history of the IGM, from the epoch of thermal decoupling of hydrogen gas and the cosmic microwave background radiation to the cosmic dawn. It is possible that two separate scenarios which predict very similar HI differential temperature during the cosmic dawn and are consistent with the EDGES 21-cm signal might have very different IGM temperature during the dark ages. The evolutions of the ionisation fraction in these two scenarios are quite different. This prohibits us to accurately calculate the ionization fraction during the cosmic dawn using the EDGES 21-cm signal alone. We find that the changes in the ionization fraction with respect to the standard scenario at redshift $z\sim 17$ could be anything between $\sim 0\%$ to $\sim 36\%$. This uncertainty may be reduced if measurements of HI 21-cm differential temperature at multiple redshifts are simultaneously used.

The coalescence of compact binary stars is expected to produce a stochastic background of gravitational waves (GWs) observable with future GW detectors. Such backgrounds are usually characterized by their power spectrum as a function of the frequency. Here, we present a method to calculate the full one-point distribution of strain fluctuations. We focus on time series data, but our approach generalizes to the frequency domain. We illustrate how this probability distribution can be evaluated numerically. In addition, we derive accurate analytical asymptotic expressions for the large strain tail, which demonstrate that it is dominated by the nearest source. As an application, we calculate the distribution of strain fluctuations for the astrophysical GW background produced by binary mergers of compact stars in the Universe, and the distribution of the observed confusion background obtained upon subtracting bright, resolved sources from the signal. We quantify the extent to which they deviate from a Gaussian distribution. Our approach could be useful for the spectral shape reconstruction of stochastic GW backgrounds.

The presence of nonzero helicity in intergalactic magnetic fields (IGMF) has been suggested as a clear signature for their primordial origin. We extend a previous analysis of diffuse Fermi-LAT gamma-ray data from 2.5 to more than 11 years and show that a hint for helical magnetic fields in the 2.5 year data was a statistical fluctuation. Then we examine the detection prospects of helical magnetic fields using individual sources as, e.g., TeV gamma-ray blazars. We find that a detection is challenging employing realistic models for the cascade evolution, the IGMF and the detector resolution in our simulations.

Variational minimization of tensor network states enables the exploration of low energy states of lattice gauge theories. However, the exact numerical evaluation of high-dimensional tensor network states remains challenging in general. In [E. Zohar and J. I. Cirac, Phys. Rev. D 97, 034510 (2018)] it was shown how, by combining gauged Gaussian projected entangled pair states with a variational Monte Carlo procedure, it is possible to efficiently compute physical observables. In this paper we demonstrate how this approach can be used to investigate numerically the ground state of a lattice gauge theory. More concretely, we explicitly carry out the variational Monte Carlo procedure based on such contraction methods for a pure gauge Kogut-Susskind Hamiltonian with a ${\mathbb{Z}}_3$ gauge field in two spatial dimensions. This is a first proof of principle to the method, which provides an inherent way to increase the number of variational parameters and can be readily extended to systems with physical fermions.

Recently, several hints of lepton nonuniversality have been observed in the semileptonic B meson decays in terms of both in the neutral current ($b\to sl\overline{l}$) and charged current ($b\to cl\overline{{\nu }_l}$) transitions. Motivated by these inspiring results, we perform the analysis of the baryon decays ${\mathrm{\Sigma }}_b\to {\mathrm{\Sigma }}_{c}l\overline{{\nu }_l}$ and ${\mathrm{\Omega }}_b\to {\mathrm{\Omega }}_{c}l\overline{{\nu }_l}(l=e,\mu ,\tau )$ which are mediated by $b\to cl\overline{{\nu }_l}$ transitions at the quark level, to scrutinize the nature of new physics (NP) in the model independent method. We first use the experimental measurements of $\mathcal{B}(B\to D^{(*)}l\overline{{\nu }_l})$, ${\mathrm{R}}_{D^{(*)}}$ and ${\mathrm{R}}_{J/\psi }$ to constrain the NP coupling parameters in a variety of scenarios. Using the constrained NP coupling parameters, we report numerical results on various observables related to the processes ${\mathrm{\Sigma }}_b\to {\mathrm{\Sigma }}_{c}l\overline{{\nu }_l}$ and ${\mathrm{\Omega }}_b\to {\mathrm{\Omega }}_{c}l\overline{{\nu }_l}$, such as the branching ratios, the ratio of branching fractions, the lepton side forward-backward asymmetries, the hadron and lepton longitudinal polarization asymmetries and the convexity parameter. We also provide the $q^2$ dependency of these observables and we hope that the corresponding numerical results in this work will be testified by future experiments.

We study anomalous magnetic moments and flavor violating processes of $e$, $\mu$, and $\tau$ leptons. We use a data driven approach to investigate the implications of the present data on the parameters of a class of models, which has spin-0 scalar and spin-$1/2$ fermion fields. We compare two different cases, which has or does not have a built-in cancelation mechanism. Our findings are as following. Chiral interactions are unable to generate large enough $\mathrm{\Delta }{a}_e$ and $\mathrm{\Delta }{a}_{\mu }$ to accommodate the experimental results. Although sizable $\mathrm{\Delta }{a}_e$ and $\mathrm{\Delta }{a}_{\mu }$ can be generated from nonchiral interactions, they are not contributed from the same source. Presently, the upper limit of $\mu \to e\gamma$ decay gives the most severe constraints on photonic penguin contributions in $\mu \to e$ transitions, but the situation may change in considering future experimental sensitivities. The $Z$-penguin diagrams can constrain chiral interaction better than photonic penguin diagrams in $\mu \to e$ transitions. In most of the parameter space, box contributions to $\mu \to 3e$ decay are subleading. The present bounds on $\mathrm{\Delta }{a}_{\tau }$ and $d_{\tau }$ are unable to give useful constraints on parameters. In $\tau \to e$ ($\mu$) transitions, the present $\tau \to e\gamma (\mu \gamma )$ upper limit constrains the photonic penguin contribution better than the $\tau \to 3e$ $(3\mu )$ upper limit, and $Z$-penguin amplitudes constrain chiral interaction better than photonic penguin amplitudes. Box contributions to $\tau \to 3e$ and $\tau \to 3\mu$ decays can sometime be comparable to $Z$-penguin contributions. The ${\tau }^{-}\to e^{-}{\mu }^{+}{e}^{-}$ and ${\tau }^{-}\to {\mu }^{-}{e}^{+}{\mu }^{-}$ rates are highly constrained by $\tau \to e\gamma$, $\mu \to e\gamma$ and $\tau \to \mu \gamma$, $\mu \to e\gamma$ upper limits, respectively. We compare the current experimental upper limits, future sensitivities and bounds from consistency on various muon and tau LFV processes.

We present a simplified derivation of the relativistic three-particle quantization condition for identical, spinless particles described by a generic relativistic field theory satisfying a ${\mathbb{Z}}_2$ symmetry. The simplification is afforded by using a three-particle quasilocal K matrix that is not fully symmetrized, ${\tilde{\mathcal{K}}}_{\mathrm{df},3}^{(u,u)}$, and makes extensive use of time-ordered perturbation theory (TOPT). We obtain a new form of the quantization condition. This new form can then be related algebraically to the standard quantization condition, which depends on a fully symmetric three-particle K matrix, ${\mathcal{K}}_{\mathrm{df},3}$. The new derivation is fully explicit, allowing, for example, a closed-form expression for ${\mathcal{K}}_{\mathrm{df},3}$ to be given in terms of TOPT amplitudes. The new form of the quantization condition is similar in structure to that obtained in the “finite-volume unitarity” approach, and in a companion paper we make this connection concrete. Our simplified approach should also allow a more straightforward generalization of the quantization condition to nondegenerate particles, and perhaps also to more than three particles.

In this article, we apply the path optimization method to handle the complexified parameters in the $1+1$ dimensional pure $U(1)$ gauge theory on the lattice. Complexified parameters make it possible to explore the Lee-Yang zeros which helps us to understand the phase structure and thus we consider the complex coupling constant with the path optimization method in the theory. We clarify the gauge fixing issue in the path optimization method; the gauge fixing helps to optimize the integration path effectively. With the gauge fixing, the path optimization method can treat the complex parameter and control the sign problem. It is the first step to directly tackle the Lee-Yang zero analysis of the gauge theory by using the path optimization method.

We study the gauge cooling technique for the complex Langevin method applied to the computation in lattice quantum chromodynamics. We propose a new solver of the minimization problem that optimizes the gauge, which does not include any parameter in each iteration, and shows better performance than the classical gradient descent method especially when the lattice size is large. Two numerical tests are carried out to show the effectiveness of the new algorithm.

An analysis is presented of elastic $P$-wave $\pi \pi$ phase shifts and inelasticities up to 2 GeV, aimed at identifying the corresponding $J^{PC}=1^{--}$ excited $\rho$ resonances and focusing on the $\rho (1250)$ vs $\rho (1450)$ controversy. The approach employs an improved parametrization in terms of a manifestly unitary and analytic three-channel $S$ matrix with its complex-energy pole positions. The included channels are $\pi \pi$, $\rho 2\pi$, and $\rho \rho$, the latter two being effective in the sense that they mimic several experimentally observed decay modes with nearby thresholds. In an alternative fit, the $\rho 2\pi$ mode is replaced by $\omega \pi$, which is also an experimentally relevant channel. The improvement with respect to prior work amounts to the enforcement of maximum crossing symmetry through once-subtracted dispersion relations called GKPY equations. A separate analysis concerns the pion electromagnetic form factor, which again demonstrates the enormous importance of guaranteeing unitarity and analyticity when dealing with very broad and highly inelastic resonances. In the case of $\rho (1250)$ vs $\rho (1450)$, the failure to do so is shown to give rise to an error in the predicted mass of about 170 MeV. A clear picture emerges from these analyses, identifying five vector $\rho$ states below 2 GeV, viz. $\rho (770)$, $\rho (1250)$, $\rho (1450)$, $\rho (1600)$, and $\rho (1800)$, with $\rho (1250)$ being indisputably the most important excited $\rho$ resonance. The stability of the fits as well as the imposition of unitarity, analyticity, and approximate crossing symmetry in the analyses lend very strong support to these assignments. The possibly far-reaching consequences for meson spectroscopy are discussed.

In this paper, the NJL-type model is used to investigate the color superconductivity. The four-fermion interactions of the NJL-type model are Fierz-transformed into two different classes, i.e., the quark-antiquark and the quark-quark interaction channels, associated with the chiral symmetry breaking and color superconductivity respectively. We conclude that the weighting factor between quark-antiquark and quark-quark interaction channels has significance on the phase structure when the mean-field approximation is employed, and the baryon number density gives a tight constraint on the weighting factor of quark-antiquark interaction channels. Besides, the susceptibilities show that the color superconducting phase transition is of the second-order and takes place before the chiral crossover transition as quark number density increases. In the end, we study the critical temperatures $T_c$ of the color superconductivity and it agrees with the perturbative result of diquark condensate $\mathrm{\Delta }\approx 0.57T_c$.

Classical scale invariance (CSI) may shed light on the weak scale origin, but the realistic CSI extension to the standard model requires a bosonic trigger. We propose a scalar dark matter (DM) field $X$ as the trigger, establishing a strong connection between the successful radiative breaking of CSI and DM phenomenologies. The latter forces the breaking scale to approximately $\mathcal{O}(\mathrm{TeV})$. It brightens the test prospect of this scenario via a gravitational wave, a sharp prediction of CSI phase transition (CSIPT), which is first order and has strong supercooling. Moreover, we carefully deal with some techniques which are commonly used to analyze CSIPT but may be missed. In particular, we clarify the imprecision of Witten’s formula used in the single field case to calculate the bubble nucleation rate and stress that the essence of Witten’s approximation is the validity of high-temperature expansion.