Monte Carlo studies of many quantum systems face exponentially severe signal-to-noise problems. We show that noise arising from complex phase fluctuations of observables can be reduced without introducing bias using path integral contour deformation techniques. A numerical study of contour deformations for correlation functions in Abelian gauge theory and complex scalar field theory demonstrates that variance can be reduced by orders of magnitude without modifying Monte Carlo sampling.

The LHCb Collaboration has recently observed three narrow pentaquark states—the $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$—that are located close to the $\overline{D}{\mathrm{\Sigma }}_c$ and ${\overline{D}}^{*}{\mathrm{\Sigma }}_c$ thresholds. Among the so-far proposed theoretical interpretations for these pentaquarks, the molecular hypothesis seems to be the preferred one. Nevertheless, in the molecular picture, the spins of the $P_c(4440)$ and $P_c(4457)$ have not been unambiguously determined yet. In this paper, we point out that heavy-antiquark-diquark symmetry induces a model-independent relation between the spin splitting in the masses of the $P_c(4440)$ and $P_c(4457){\overline{D}}^{*}{\mathrm{\Sigma }}_c$ pentaquarks and the corresponding splitting for the $0^{+}$ and $1^{+}$ ${\mathrm{\Xi }}_{cc}{\mathrm{\Sigma }}_c$ triply charmed dibaryons. This is particularly relevant owing to a recent lattice-QCD prediction of the $1^{+}$ triply charmed dibaryon, which suggests that a calculation of the mass of its $0^{+}$ partner might be within reach. This, in turn, would reveal the spins of the $P_c(4440)$ and $P_c(4457)$ pentaquarks, providing a highly nontrivial test of heavy-quark symmetry and the molecular nature of the pentaquarks. Furthermore, the molecular interpretation of the hidden-charm pentaquarks implies the existence of a total of ten triply charmed dibaryons as ${\mathrm{\Xi }}_{cc}^{(*)}{\mathrm{\Sigma }}_c^{(*)}$ molecules, which, if confirmed in the lattice, will largely expand our understanding of the nonperturbative strong interaction in the heavy-quark sector.

We present a next-to-next-to-leading order (NNLO) calculation of the quasiparton distribution functions (quasi-PDFs) in the large momentum effective theory (LaMET). We focus on the flavor nondiagonal quark-quark channel and demonstrate the LaMET factorization at the NNLO accuracy in the modified minimal subtraction scheme. The matching coefficient between the quasi-PDF and the light-cone PDF is derived. This provides a first step towards a complete NNLO analysis of quasi-PDFs and to better understand the nucleon structures from the first principle of QCD.

We propose a deep learning method to build an AdS/QCD model from the data of hadron spectra. A major problem of generic AdS/QCD models is that a large ambiguity is allowed for the bulk gravity metric with which QCD observables are holographically calculated. We adopt the experimentally measured spectra of $\rho$ and $a_2$ mesons as training data, and perform a supervised machine learning which determines concretely a bulk metric and a dilaton profile of an AdS/QCD model. Our deep learning (DL) architecture is based on the AdS/DL correspondence [K. Hashimoto, S. Sugishita, A. Tanaka, and A. Tomiya, Phys. Rev. D 98, 046019 (2018)] where the deep neural network is identified with the emergent bulk spacetime.

Commutation or anticommutation relations quantized at equal instant time and commutation or anticommutation relations quantized at equal light-front time not only cannot be transformed into each other, they take completely different forms. While they would thus appear to describe different theories, we show that this is not in fact the case. By looking not at equal times but at unequal times, we show that unequal instant-time commutation or anticommutation relations are completely equivalent to unequal light-front time commutation or anticommutation relations. Light-front quantization and instant-time quantization are thus the same and thus describe the same theory, with it being only the restriction to equal times that makes them look different. However, for fermions there is a caveat, as the light-front anticommutation relations involve projection operators acting on the fermion fields. Nonetheless, not only can one still derive fermion unequal light-front time anticommutators starting from unequal instant-time ones, one can even derive unequal instant-time fermion anticommutators starting from unequal light-front time anticommutators even though the fermion projection operators that are relevant in the light-front case are not invertible. To establish the equivalence for gauge fields we present a quantization procedure that does not involve the zero-mode singularities that are commonly encountered in light-front gauge field studies. We also study time-ordered products of fields, and again show the equivalence despite the fact that there are additional terms in the fermion light-front case. We establish our results first for free theories, and then to all orders in interacting theories though comparison of the instant-time and light-front Lehmann representations. Finally, we compare instant-time Hamiltonians and light-front Hamiltonians and show that in the instant-time rest frame they give identical results.

We propose accurate calculations of quasinormal modes of black holes in the Einstein-aether theory, which were previously considered in the literature, partially, with insufficient accuracy. We also show that the arbitrarily long-lived modes, quasiresonances, are allowed in the Einstein-aether theory as well and demonstrate that the asymptotic tails, unlike quasinormal frequencies, are indistinguishable from those in the Einstein theory.

The propagation of electromagnetic waves in vacuum is often described within the geometrical optics approximation, which predicts that wave rays follow null geodesics. However, this model is valid only in the limit of infinitely high frequencies. At large but finite frequencies, diffraction can still be negligible, but the ray dynamics becomes affected by the evolution of the wave polarization. Hence, rays can deviate from null geodesics, which is known as the gravitational spin Hall effect of light. In the literature, this effect has been calculated ad hoc for a number of special cases, but no general description has been proposed. Here, we present a covariant Wentzel-Kramers-Brillouin analysis from first principles for the propagation of light in arbitrary curved spacetimes. We obtain polarization-dependent ray equations describing the gravitational spin Hall effect of light. We also present numerical examples of polarization-dependent ray dynamics in the Schwarzschild spacetime, and the magnitude of the effect is briefly discussed. The analysis reported here is analogous to that of the spin Hall effect of light in inhomogeneous media, which has been experimentally verified.

It is well known that general relativity in three spacetime dimensions (3D) has no well-defined Newtonian limit. Recently, a static solution mimicking the behavior of the expected Newtonian potential has been found by studying the classical double copy of a point charge in gauge theory [M. Carrillo Gonzlez, B. Melcher, K. Ratliff, S. Watson, and C. D. White, J. High Energy Phys. 07 (2019) 167.]. This is the first example where the vacuum solution in the gauge theory leads to a nonvacuum solution on the gravity side. The resulting energy-momentum tensor was attributed to a free scalar ghost field; however, alternatively, the source can be seen as one resulting from a spacelike perfect fluid. In this paper, we first give an alternative derivation of the solution where there is no need to perform a generalized gauge transformation to obtain a quadratic Lagrangian without propagating ghost fields. Then, we present a stationary version of the solution and show that the scalar field interpretation of the source does not survive in this case, leaving the spacelike fluid as the only possibility. We give the gauge theory single copy of our solution and comment on the implications of our results on the validity of the classical double copy in 3D. The effect of the cosmological constant is also discussed.

We demonstrate the existence of sudden finite-time singularities, with constant scale factor, expansion rate, and density, in expanding Bianchi type-IX universes with free anisotropic pressures. A new type of nonsimultaneous anisotropic sudden singularity arises because of the divergences of the pressures, which may be of barrel or pancake type. The effect of one or more directions of expansion hitting a sudden singularity is tantamount to dimensional reductions as the nonsingular directions continue expanding and can see the sudden singularity in their past.

In this paper, we explore the formation of the marginally trapped/ antitrapped surfaces that arise from the evolution of dust in $D$-dimensions with and without the cosmological constant. We obtain analytical expressions for such surfaces. We also derive closed form expressions for the norms of various quantities that decide the Causal nature of the marginally trapped/antitrapped surfaces. We discuss several interesting features of evolution of these surfaces that are significantly different from the four dimensional counterpart. We obtain the expressions for the Ashtekar-Badrikrihnan’s area-balance law for dynamical horizon (spacelike surface) tailored for the case of spherically symmetric dust evolution in $D$-dimensions.

Motivated by a scenario of magnetogenesis in which a homogeneous magnetic field is generated during inflation, we study the magnetohydrodynamic evolution of the primordial plasma motions for two kinds of initial conditions—(i) a spatially homogeneous field with an unlimited correlation length, and (ii) a zero flux scale-invariant statistically homogeneous magnetic field. In both cases, we apply, for a short initial time interval, monochromatic forcing at a certain wave number so that the correlation length is finite, but much smaller than the typical length scale of turbulence. In particular, we investigate the decay of nonhelical and helical hydromagnetic turbulence. We show that, in the presence of a homogeneous magnetic field, the decay of helical and nonhelical small-scale fields can occur rapidly. This is a special property of a system with a perfectly homogeneous magnetic field, which is sometimes considered as a local approximation to a slowly varying background field. It can never change and acts as an imposed magnetic field. This is in sharp contrast to the case of a statistically homogeneous magnetic field, where we recover familiar decay properties: a much slower decay of magnetic energy and a faster growth of the correlation length, especially in the case with magnetic helicity. The result suggests that a homogeneous magnetic field, if generated during inflation, should persist under the influence of small-scale fields and could be the origin of the large-scale magnetic field in the Universe.

We investigate systematically the quark-hadron mixed phase in dense stellar matter and its influence on compact star structures. The properties of quark matter and hadronic matter are fixed based on various model predictions. Beside adopting constant values, the surface tension $\mathrm{\Sigma }$ for the quark-hadron interface is estimated with the multiple reflection expansion method and equivparticle model. To fix the structures of quark-hadron pasta phases, a continuous dimensionality of the structure is adopted as proposed by Ravenhall et al. The corresponding properties of hybrid stars are then obtained and confronted with pulsar observations. It is found that the correlation between radius and tidal deformability in traditional neutron stars preserves in hybrid stars. For those permitted by pulsar observations, in almost all cases, the quark phase persists inside the most massive compact stars. The quark-hadron interface plays an important role in hybrid star structures once quark matter emerges. The surface tension $\mathrm{\Sigma }$ estimated with various methods increases with density, which predicts stiffer equation of states (EOSs) for the quark-hadron mixed phase and increases the maximum mass of hybrid stars. With or without the emergence of quark matter, the obtained EOSs of hybrid star matter are close to each other at densities $n\lesssim 0.8{\mathrm{fm}}^{-3}$, while larger uncertainty is expected at higher densities.

A wide range of mechanisms predict present-day $s$-wave dark matter (DM) annihilation cross sections that are orders of magnitude below current experimental sensitivity. We explore the capability of DM density spikes around the Milky Way’s supermassive black hole to probe such faint signals of DM annihilations, considering a range of possible spike and halo distributions. As an exemplar of a theory with a suppressed $s$-wave annihilation cross section, we consider a hidden sector axion portal model of DM. In this model, the leading contribution to the annihilation cross section in the early Universe is $p$-wave, while $s$-wave annihilations occur at higher order in the coupling constant. We provide a unified treatment of DM freeze-out in this model including both $s$- and $p$-wave annihilations and analytically determine the photon spectrum for the dominant DM annihilation process in the Universe today. We find that Fermi and H.E.S.S. observations of the Galactic center offer excellent sensitivity to this model over a wide range of parameter space, with prospects depending sensitively on the properties of the DM spike as well as the central halo.

We calculate the effective $J$-factors, which determine the strength of indirect detection signals from dark matter annihilation, for 25 dwarf spheroidal galaxies (dSphs). We consider several well-motivated assumptions for the relative velocity dependence of the dark matter annihilation cross section: ${\sigma }_{A}v$: $s$-wave (velocity independent), $p$-wave (${\sigma }_{A}v\propto v^2$), $d$-wave (${\sigma }_{A}v\propto v^4$), and Sommerfeld-enhancement in the Coulomb limit (${\sigma }_{A}v\propto 1/v$). As a result we provide the largest and most updated sample of $J$-factors for velocity-dependent annihilation models. For each scenario, we use Fermi-LAT gamma-ray data to constrain the annihilation cross section. Due to the assumptions made in our gamma-ray data analysis, our bounds are comparable to previous bounds on both the $p$-wave and Sommerfeld-enhanced cross sections using dSphs. Our bounds on the $d$-wave cross section are the first such bounds using indirect detection data.

Upgrades to improve the sensitivity of gravitational wave detectors enable more frequent detections and more precise source parameter estimation. Unlike other advanced interferometric detectors such as Advanced LIGO and Advanced Virgo, KAGRA requires a different approach for the upgrade since it is the only detector which employs cryogenic cooling of the test masses. In this paper, we describe possible KAGRA upgrades with technologies focusing on different detector bands and compare the impacts on the detection of compact binary coalescences. We show that either fivefold improvement in the $100M_{\odot }–100M_{\odot }$ binary black hole range, a factor of 1.3 improvement in the binary neutron star range, or a factor of 1.7 improvement in the sky localization of binary neutron stars is quite feasible with upgrades that do not require changes in the existing cryogenic or vacuum infrastructure. We also show that twofold broadband sensitivity improvement is possible by applying multiple upgrades to the detector.

The thermal transport coefficients in a weakly magnetized quark-gluon plasma have been investigated within the ambit of a quasiparticle model to encode the effects of the realistic equation of state. The presence of a weak magnetic field leads to the Hall-type conductivity associated with thermal transport in the medium. An effective covariant kinetic theory has been employed to quantify the thermal dissipation while incorporating the mean field contributions in the medium. The interplay of thermal transport and electric charge transport in the weakly magnetized medium has been explored in terms of the Wiedemann-Franz law. Strong violation of the Wiedemann-Franz law has been observed in temperature regimes near to the transition temperature. The behavior of thermal conductivity in the strong magnetic field limit has also been studied. It is observed that both the magnetic field and equation of state have a significant impact on the thermal dissipation in the medium.

We find that the recently developed kinetic theories with spin for massive and massless fermions are smoothly connected. By introducing a reference-frame vector, we decompose the dipole-moment tensor into electric and magnetic dipole moments. We show that the axial-vector component of the Wigner function contains a contribution from the transverse magnetic dipole moment, which accounts for the transverse spin degree of freedom (d.o.f.) and vanishes smoothly in the massless limit. As a result, the kinetic equations, describing 4 d.o.f. for massive fermions, smoothly becomes the chiral kinetic equations describing 2 d.o.f. in the massless limit. We also confirm the small-mass behavior of the Wigner function by an explicit calculation using a Gaussian wave packet.

We investigate how the propagation of an astrophysical gravitational wave background (AGWB) is modified over cosmological volumes when considering theories beyond general relativity of the type Horndeski gravity. We first deduce an amplitude correction on the AGWB induced for the presence of a possible running in the Planck mass. Then, we apply the spectral noise density from some ground-based interferometers, namely, the Advanced LIGO (aLIGO), Einstein Telescope (ET) and Cosmic Explore (CE), to evaluate the signal-to-noise ratio as a function of the amplitude of the running of the Planck mass for two different scenarios. We find that for observation time period $\gtrsim 5\mathrm{yrs}$ and $\gtrsim 1\mathrm{yr}$, we can have a significant signal of the AGWB in the band [1–100] Hz from the ET and CE sensitivity, respectively. Finally, using Fisher information, we find some forecast bounds, and we deduce $\lesssim 27\%$ and $\lesssim 18\%$ correction at $1\sigma$ confidence level on the amplitude of the running of the Planck mass from ET and CE, respectively. It is clear that a detection of a AGWB in the future can open a new window to probe the nature of gravity with good accuracy.