One may believe that front velocities of waves in a given theory coincide with the UV limit of phase velocities for any dispersion relations. This implies that IR physics is irrelevant to the discussion of propagation speed of waves. We first consider a theory that contains higher spatial derivatives in the wave equation and prove that front velocities coincide with the UV limit of phase velocities, at least, if parity is conserved. However, we also show that front velocities do not coincide with the UV limit of phase velocities in general dispersion relations. We explicitly give several examples in which front velocities are superluminal owing to an IR or intermediate energy scale property of dispersion relations even if the UV limit of phase velocities is luminal. Our finding conveys the important caution that not only UV physics but also IR physics can be significant to superluminality.

Several neutrino experiments have reported results that are potentially inconsistent with our current understanding of the lepton sector. A candidate solution to these so-called short-baseline anomalies is postulating the existence of new, eV-scale, mostly sterile neutrinos that mix with the active neutrinos. This hypothesis, however, is strongly disfavored once one considers all neutrino data, especially those that constrain the disappearance of muon and electron neutrinos at short baselines. Here, we show that if the sterile-active mixing parameters depend on the energy scales that characterize neutrino production and detection, then the sterile-neutrino hypothesis may provide a reasonable fit to all neutrino data. The reason for the improved fit is that the stringent disappearance constraints on the different elements of the extended neutrino mixing matrix are associated to production and detection energy scales that are different from those that characterize the anomalous appearance data at MiniBooNE. We show, via a concrete example, that secret interactions among the sterile neutrinos can lead to the results of interest.

Using a geometric description of 2HDM, the $CP$-odd invariants are classified into three independent sectors: scalar potential, Yukawa interaction, and CKM matrix. We calculate the effective thermal potential of 2HDM in a basis invariant way and show that the $CP$ phases in the CKM matrix cannot leak to the effective potential at all orders. In the 2HDM with a softly broken $Z_2$ symmetry, the leading thermal correction to the effective potential tends to restore the $CP$ symmetry at high temperatures.

Recalling the expectation of an extremely strong primordial magnetic field $H$, we recheck transitions among the phases of chiral symmetry restoration ($\chi SR$), chiral symmetry breaking ($\chi SB$), and pion superfluidity ($\pi SF$) in the QCD epoch of the early universe. For homogeneous phases in a finite $H$, a sensible scheme is adopted to determine the phase boundaries of $\pi SF$, which is also the superconductivity phase itself. In the first part, the QCD phase diagrams are studied in detail within the chiral effective Polyakov-Nambu–Jona-Lasinio model, and the transitions involving $\pi SF$ are found to be of first order at relatively small $H$. As expected from the Meissner effect, the regime of $\pi SF$ shrinks with increasing $H$ and completely vanishes beyond a threshold value. In the second part, the bubble dynamics is illuminated for the stronger first-order transition, $\chi SR\to \pi SF$, in the more convenient Polyakov-quark-meson model. The coupled equations of motion of pion condensate and magnetic field are solved consistently to give the bubble structure. Then, based on bubble collisions, we explore gravitational wave (GW) emission by developing a simple toy model in advance; and the characteristic frequency of the relic GW is estimated to be of the order 0.1–1 K or ${10}^9–{10}^{10}\mathrm{Hz}$ in our galaxy.

The recent holographic deduction of the Penrose inequality only assumes the null energy condition, while a weak or dominant energy condition is required in the usual geometric proof. We take a step toward filling the gap between these two approaches. For planar or spherically symmetric asymptotically Schwarzschild anti-de Sitter (AdS) black holes, we give a purely geometric proof for the Penrose inequality by assuming the null energy condition. We also point out that two naive generalizations of the charged Penrose inequality are generally not true, and we propose two new candidates. When the spacetime is asymptotically AdS but not Schwarzschild-AdS, the total mass is defined according to holographic renormalization and depends on the scheme of quantization. In this case, the holographic argument implies that the Penrose inequality should still be valid, but we use a concrete example to show that whether the Penrose inequality holds or not will depend on what kind of quantization scheme we employ.

We evaluate reflected entropy in certain anisotropic boundary theories dual to nonrelativistic geometries using holography. It is proposed that this quantity is proportional to the minimal area of the entanglement wedge cross section. Using this prescription, we study in detail the effect of anisotropy on reflected entropy and other holographic entanglement measures. In particular, we study the discontinuous phase transition of this quantity for a symmetric configuration consisting of two disjoint strips. We find that in the specific regimes of the parameter space the critical separation is an increasing function of the anisotropy parameter and hence the correlation between the subregions becomes more pronounced. We carefully examine how these results are consistent with the behavior of other correlation measures including the mutual information. Finally, we show that the structure of the universal terms of entanglement entropy is corrected depending on the orientation of the entangling region with respect to the anisotropic direction.

Three-dimensional Lorentzian quantum gravity, expressed as the continuum limit of a nonperturbative sum over spacetimes, is tantalizingly close to being amenable to analytical methods, and some of its properties have been described in terms of effective matrix and other models. To gain a more detailed understanding of three-dimensional quantum gravity, we perform a numerical investigation of the nature of spatial hypersurfaces in three-dimensional causal dynamical triangulations (CDT). We measure and analyze several quantum observables, the entropy exponent, the local and global Hausdorff dimensions, and the quantum Ricci curvature of the spatial slices, and try to match them with known continuum properties of systems of two-dimensional quantum geometry. Above the first-order phase transition of CDT quantum gravity, we find strong evidence that the spatial dynamics lies in the same universality class as two-dimensional Euclidean (Liouville) quantum gravity. Below the transition, the behavior of the spatial slices does not match that of any known quantum gravity model. This may indicate the existence of a new type of two-dimensional quantum system, induced by the more complex nature of the embedding three-dimensional quantum geometry.

We investigate spectral functions of matter-gauge theories that are asymptotically free in the ultraviolet and display a Banks-Zaks conformal fixed point in the infrared. Using perturbation theory, Callan-Symanzik resummations, and UV-IR connecting renormalization group trajectories, we analytically determine the gluon, quark, and ghost propagators in the entire complex momentum plane. At weak coupling, we find that a Källén-Lehmann spectral representation of propagators is achieved for all fields, and determine suitable ranges for gauge-fixing parameters. At strong coupling, a proliferation of complex conjugated branch cuts renders a causal representation impossible. We also derive relations for scaling exponents that determine the presence or absence of propagator nonanalyticities. Further results include spectral functions for all fields up to five loop order, bounds on the conformal window, and an algorithm to find running gauge coupling analytically at higher loops. Implications of our findings and extensions to other theories are discussed.

In this paper, we investigate the topological numbers for the singly rotating Kerr black holes in all dimensions and the four-dimensional Kerr-Newman black hole. We show that for uncharged black holes, the rotation parameter has a significant effect on the topological number, and for rotating black holes, the dimension of spacetimes has a remarkable effect on the topological number too. In addition, we find that the topological numbers of the four-dimensional Kerr and Kerr-Newman black holes are the same, which seems to indicate that the electric charge parameter has no effect on the topological number of rotating black holes. Our current research provides more evidence that the conjecture put forward in Wei et al. [Phys. Rev. Lett., 129, 191101 (2022)], according to which all black hole solutions should be separated into three different topological classes, is accurate, at least in the pure Einstein-Maxwell gravity theory.

We investigate the scalar, gravitational, and electromagnetic quasinormal mode spectra of Schwarzschild anti–de Sitter black holes using the numerical continued fraction method. The spectra have similar, almost linear structures. With a few exceptions, the low overtone quasinormal modes are consistent with previously obtained results in the literature that use other numerical techniques. The intermediate and high overtone quasinormal modes, in comparison to the Schwarzschild case, converge very quickly to the asymptotic formulas previously obtained by analytic monodromy techniques. In addition, we find a connection between the analytic asymptotic formulas and the purely imaginary modes. In particular, these formulas can be used to predict the bifurcation of the lowest damped electromagnetic modes. Finally, we find no high overtone quasinormal modes with high oscillation frequency and low damping, which had been previously predicted.

We systematically investigate the microlensing effect of a charged spherically symmetric wormhole, where the light source is remote from the throat. Remarkably, there will be at most three images by considering the charge part. We study all the situations including three images, two images, and one image, respectively. The numerical result shows that the range of total magnification is from ${10}^5$ to ${10}^{-2}$ depending on various metrics. In the case of three images, there will be two maximal values of magnification (a peak and a gentle peak) when the contribution via mass is much less than that of charge. However, we cannot distinguish the case that forms three images or only one image as the total magnification is of order ${10}^5$. Finally, our theoretical investigation could shed new light on exploring the wormhole with the microlensing effect.

Accurate waveform models describing the complete evolution of compact binaries are crucial for the maximum likelihood detection framework, testing the predictions of general relativity (GR) and investigating the possibility of an alternative theory of gravity. Deviations from general relativity could manifest in subtle variations of the numerical value of the gravitational wave signal’s phasing coefficients. Once the search pipelines confirm an unambiguous signal detection, deviations of the signal phasing coefficients at various post-Newtonian orders are routinely measured and reported. As the search templates themselves do not incorporate any deviations from general relativity, they may miss astrophysical signals carrying a significant departure from GR. We present a parametrized template-based search for exotic gravitational-wave signals beyond general relativity by incorporating deviations to the signal’s phasing coefficients at different post-Newtonian orders in the search templates. We present critical aspects of the new search, such as improvements in search volume and its effect on various parts of the parameter space. In particular, we demonstrate a twofold increase in search sensitivity (at a fixed false-alarm rate) to beyond-GR exotic signals by using search templates that admit a range of departures from general relativity. We also present the results from a reanalysis of ten days long duration of LIGO data from the first science run that includes the epoch of the GW150914 event.

The kinetic Sunyaev Zel’dovich (kSZ) effect, cosmic microwave background (CMB) temperature anisotropies induced by the scattering of CMB photons from free electrons, will be measured by near-term CMB experiments at high significance. By combining CMB temperature anisotropies with a tracer of structure, such as a galaxy redshift survey, previous literature introduced a number of techniques to reconstruct the radial velocity field. This reconstructed radial velocity field encapsulates the majority of the cosmological information contained in the kSZ temperature anisotropies, and can provide powerful new tests of the standard cosmological model and theories beyond it. In this paper, we introduce a new estimator for the radial velocity field based on a coarse-grained maximum likelihood fit for the kSZ component of the temperature anisotropies, given a tracer of the optical depth. We demonstrate that this maximum likelihood estimator yields a higher fidelity reconstruction than existing quadratic estimators in the low-noise and high-resolution regime targeted by upcoming CMB experiments. We describe implementations of the maximum likelihood estimator in both harmonic space and map space, using either direct measurements of the optical depth field or a galaxy survey as a tracer. We comment briefly on the impact of biases introduced by imperfect reconstruction of the optical depth field.

We introduce a way of measuring $H_0$ from a combination of independent geometrical data sets, without the need for calibration or the choice of a cosmological model. We build on the distance duality relation, which sets the ratio of the luminosity and angular diameter distance to a fixed scaling in redshift for any metric theory of gravity with standard photon propagation and constitutes a founding block of any theory describing our Universe. Our method allows us to determine $H_0$ from first principles, unleashing the measurement of this fundamental constant from calibration and the assumption of a cosmological model. We find $H_0=69.5\pm 1.7\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$ at 68% C.L., showing that the Hubble constant can be constrained at the percent level with minimal assumptions.

Primordial black holes (PBHs) could be formed if large perturbations are generated on small scales in inflation. We study a toy inflation model with a local minimum. The curvature perturbations are enhanced when the inflaton passes through the local minimum, with more efficient amplification rate than that of quasi-inflection point inflation, leading to the production of PBHs on small scales. The PBHs could comprise the total dark matter in the mass window ${10}^{16}–{10}^{20}\mathrm{g}$.

The prompt contribution to the atmospheric neutrino flux is analyzed. We demonstrate that the corresponding theoretical uncertainties related to perturbative treatment of charm production, notably, the ones stemming from the low- and high-$x$ behavior of parton distribution functions, can be conveniently studied at the level of charm quark production. Additionally, we discuss the nonperturbative contribution to the prompt neutrino flux, related to the intrinsic charm content of the proton and analyze its main features.

The Markov Chain Monte Carlo approach is frequently used within a Bayesian framework to sample the target posterior distribution. Its efficiency strongly depends on the proposal distribution used to build the chain. The best jump proposal is the one that closely resembles the unknown target distribution; therefore, we suggest an adaptive proposal distribution based on kernel density estimation (KDE). We group the model’s parameters according to their correlation and build a KDE based on the already accepted points for each group. We update the KDE-based proposal until it stabilizes. We argue that such a proposal distribution could be efficient in applications where the data volume is increasing. We tested it on several astrophysical datasets (IPTA and LISA) and have shown that, in some cases, the KDE-based proposal also helps to reduce the chains’ autocorrelation length. The efficiency of this proposal distribution is reduced in case of strong correlations between a large group of parameters.

Decihertz Interferometer Gravitational Wave Observatory (DECIGO) is a future mission for a space-borne laser interferometer. DECIGO has 1000-km-long arm cavities mainly to detect the primordial gravitational waves (PGWs) at lower frequencies around 0.1 Hz. Observations in the electromagnetic spectrum have lowered the bounds on the upper limit of PGWs energy density (${\mathrm{\Omega }}_{\mathrm{gw}}\sim {10}^{-15}\to {10}^{-16}$). As a result, DECIGO’s target sensitivity, which is mainly limited by quantum noise, needs further improvement. To maximize the feasibility of detection while constrained by DECIGO’s large diffraction loss, a quantum locking technique with an optical spring was theoretically proposed to improve the signal-to-noise ratio of the PGWs. In this paper, we experimentally verify one key element used in the theory: sensitivity optimization by completing the square of multiple detector outputs. This experiment is operated on a simplified tabletop optical setup with classical noise simulating quantum noise. We succeed in getting the best of the sensitivities with two different laser powers by the square completion method.

A mutilated model is constructed to approximate the collision term of spin Boltzmann equation that incorporates newly appearing collisional invariants, i.e., the total angular momentum. With recourse to degenerate perturbation theory, the dispersion relations of hydrodynamic modes are formulated, among which spin modes are responsible for spin equilibration. We find that the nonlocality does not change the sound speed but slows down the propagation of spin channel waves. The damping rates of spin modes are close to those of spinless modes over a reasonable parameter value range. The results reveal that both spin and momentum should be treated simultaneously in a unified transport framework. In the nonrelativistic limit, the short-wavelength behavior for normal modes is also explored and there exists a critical point for every distinct discrete mode over which only quasiparticle modes contribute.