In this paper, we show that QCD at high energies leads to the multiplicity distribution ${(\sigma }_n/{\sigma }_{\mathrm{in}})=(1/N){(N-1/N)}^{n-1}$ (where $N$ denotes the average number of particles) and to entanglement entropy $S=\ln N$, confirming that the partonic state at high energy is maximally entangled. However, the value of $N$ depends on the kinematics of the parton cascade. In particular, for deep inelastic scattering, $N=xG(x,Q)$, where $xG$ is the gluon structure function, while for hadron-hadron collisions, $N\propto Q_S^2(Y)$, where $Q_s$ denotes the saturation scale. We checked that this multiplicity distribution describes the LHC data for low multiplicities $n<(3÷5)N$, exceeding it for larger values of $n$. We view this as a consequence of our assumption that the system of partons in hadron-hadron collisions at c.m. rapidity $Y=0$, is dilute. We show that the data can be described at large multiplicities in the parton model, if we do not make this assumption.

The ${\mathrm{\Xi }}_c^0$ baryon is unstable and usually decays into charmless final states by the $c\to su\overline{d}$ transition. It can, however, also disintegrate into a ${\pi }^{-}$ meson and a ${\mathrm{\Lambda }}_c^{+}$ baryon via $s$ quark decay or via $cs\to dc$ weak scattering. The interplay between the latter two processes governs the size of the branching fraction $\mathcal{B}({\mathrm{\Xi }}_c^0\to {\pi }^{-}{\mathrm{\Lambda }}_c^{+})$, first measured here to be $(0.55\pm 0.02\pm 0.18)\%$, where the first uncertainty is statistical and second systematic. This result is compatible with the larger of the theoretical predictions that connect models of hyperon decays using partially conserved axial currents and SU(3) symmetry with those involving the heavy-quark expansion and heavy-quark symmetry. In addition, the branching fraction of the normalization channel, $\mathcal{B}({\mathrm{\Xi }}_c^{+}\to p{K}^{-}{\pi }^{+})=(1.135\pm 0.002\pm 0.387)\%$ is measured.

The strong cosmic censorship conjecture proposes that starting from generic initial data on some Cauchy surface, the solutions of the Einstein equation should not be extendable across the boundary of the domain of dependence of that surface. For the case of the Reissner–Nordström–de Sitter spacetime this means that any perturbation should blow up sufficiently badly when approaching this boundary, called the Cauchy horizon. However, recent results indicate that for highly charged black holes classical scalar perturbations allow for a violation of strong cosmic censorship. In a recent paper [S. Hollands et al., Classical Quantum Gravity 37, 115009 (2020)], two of us have argued that quantum effects will restore censorship for generic values of the black-hole parameters. But, due to practical limitations, the precise form of the divergence was only calculated for a small number of parameters. Here we perform a thorough parameter scan using an alternative, more efficient semianalytic method. Our analysis confirms [S. Hollands et al., Classical Quantum Gravity 37, 115009 (2020)] in the sense that the quantum stress tensor is found to diverge badly generically. However, the sign of the divergence can be changed by changing the mass of the field or the spacetime parameters, leading to a drastically different type of singularity on the Cauchy horizon.

We construct explicit mode expansions of various tree-level propagators in the Rindler–de Sitter universe, also known as the static (or compact) patch of the de Sitter spacetime. We construct in particular the Wightman functions for thermal states having a generic temperature $T$. We give a fresh simple proof that the only thermal Wightman propagator that respects the de Sitter isometry is the restriction to the Rindler–de Sitter wedge of the propagator for the Bunch-Davies state. It is the thermal state with $T=(2\pi {)}^{-1}$ in the units of de Sitter curvature. We show that propagators with $T\ne (2\pi {)}^{-1}$ are only time translation invariant and have extra singularities on the boundary of the static patch. We also construct the expansions for the so-called alpha-vacua in the static patch and discuss the flat limit.

We present and analyze a class of exact spacetimes which describe accelerating black holes with a Newman-Unti-Tamburino (NUT) parameter. First, by two independent methods we verify that the intricate metric found by Chng, Mann, and Stelea in 2006 indeed solves Einstein’s vacuum field equations of general relativity. We explicitly calculate all components of the Weyl tensor and determine its algebraic structure. As it turns out, it is actually of algebraically general type I with four distinct principal null directions. It explains why this class of solutions has not been (and could not be) found within the large Plebański–Demiański family of type D spacetimes. Then we transform the solution into a much more convenient metric form which explicitly depends on three physical parameters: mass $m$, acceleration $\alpha$, and the NUT parameter $l$. These parameters can independently be set to zero, recovering thus the well-known spacetimes in standard coordinates, namely the $C$-metric, the Taub–NUT metric, the Schwarzschild metric, and flat Minkowski space in spherical coordinates. Using this new metric, we investigate main physical and geometrical properties of such accelerating NUT black holes. In particular, we localize and study four Killing horizons (two black-hole plus two acceleration horizons) and carefully investigate the curvature. Employing the scalar invariants we prove that there are no curvature singularities whenever the NUT parameter is nonzero. We identify asymptotically flat regions and relate them to conformal infinities. This leads to a complete understanding of the global structure of the spacetimes: each accelerating NUT black hole is a “throat” which connects “our universe” with a “parallel universe.” Moreover, the analytic extension of the boost-rotation metric form reveals that there is a pair of such black holes (with four asymptotically flat regions). They uniformly accelerate in opposite directions due to the action of rotating cosmic strings or struts located along the corresponding two axes. Rotation of these sources is directly related to the NUT parameter. In their vicinity there are pathological regions with closed timelike curves.

Cataldo has found all rigidly rotating self-gravitating perfect fluid solutions in $2+1$ dimensions with a negative cosmological constant $\mathrm{\Lambda }$, for a density that is specified a priori as a function of a certain radial coordinate. We rewrite these solutions in standard polar-radial coordinates, for an arbitrary barotropic equation of state $p(\rho )$. For any given equation of state, we find the two-parameter family of solutions with a regular center and finite total mass $M$ and angular momentum $J$ (rigidly rotating stars). For analytic equations of state, the solution is analytic except at the surface, but including at the center. Defining the dimensionless spin $\tilde{J}≔\sqrt{-\mathrm{\Lambda }}J$, there is precisely one solution for each $(\tilde{J},M)$ in the region $|\tilde{J}|-1<M<|\tilde{J}|$, which consists of parts of the point-particle region $M<-|\tilde{J}|$ and overspinning regions $|\tilde{J}|>|M|$. In an adjacent compact part of the black-hole region $|\tilde{J}|<M$ (whose extent depends on the equation of state), there are precisely two solutions for each $(\tilde{J},M)$. Hence, exterior solutions exist in all three classes of Bañados, Teitelboim, and Zanelli solution (black hole, point particle, and overspinning), but not all possible values of $(\tilde{J},M)$ can be realized as stars. Regardless of the values of $\tilde{J}$ and $M$, the causal structure of all stars for all equations of state is that of anti–de Sitter space, without horizons or closed timelike curves.

Noncommutative gravity is a natural method of quantizing spacetime by promoting the spacetime coordinates themselves to operators which do not commute. This approach is motivated from a quantum gravity perspective, as well as from other theoretical considerations. Noncommutative gravity has been tested against the binary black hole merger event GW150914. Here, we extend and improve upon such a previous analysis by (i) relaxing an assumption made on the preferred direction due to noncommutativity, (ii) using posterior samples produced by the LIGO/Virgo Collaborations, (iii) consider other gravitational wave events, namely GW151226, GW170608, GW170814 and GW170817, and (iv) considering binary pulsar observations. Using Kepler’s law that contains the noncommutative effect at second post-Newtonian order, we derive corrections to the gravitational waveform phase and the pericenter precession. Using the gravitational wave and double pulsar binary observations, we find bounds on a space-time noncommutative tensor ${\theta }^{0i}$ in terms of the preferred frame direction with respect to the orientation of each binary. We find that the gravitational wave bounds are stronger than the binary pulsar one by an order of magnitude and the noncommutative tensor normalized by the Planck length and time is constrained to be of order unity.

We derive constraints on primordial power spectrum, for the first time, from galaxy UV luminosity functions (LFs) at high redshifts. Since the galaxy LFs reflect an underlying halo mass function which depends on primordial fluctuations, one can constrain primordial power spectrum, particularly on small scales. We perform a Markov Chain Monte Carlo analysis by varying parameters for primordial power spectrum as well as those describing astrophysics. We adopt the UV LFs derived from Hubble Frontier Fields data at $z=6–10$, which enable us to probe primordial fluctuations on the scales of $k\sim 10–{10}^3{\mathrm{Mpc}}^{-1}$. Our analysis also clarifies how the assumption on cosmology such as primordial power spectrum affects the determination of astrophysical parameters.

We explore the covariance of redshift-space matter power spectra after a standard density-field reconstruction. We derive perturbative formula of the covariance at the tree-level order and find that the amplitude of the off-diagonal components from the trispectrum decreases by reconstruction. Using a large set of $N$-body simulations, we also find the similar reduction of the off-diagonal components of the covariance and thereby the signal-to-noise ratio (S/N) of the postreconstructed (postrec) power spectra significantly increases compared to the prereconstructed spectra. This indicates that the information leaking to higher-order statistics come back to the two-point statistics by reconstruction. Interestingly, the postrec spectra have higher S/N than the linear spectrum with Gaussian covariance when the scale of reconstruction characterized with the smoothing scale of the shift field is below $\sim 10h^{-1}\mathrm{Mpc}$ where the trispectrum becomes negative. We demonstrate that the error of the growth rate estimated from the monopole and quadrupole components of the redshift-space matter power spectra significantly improves by reconstruction. We also find a similar improvement of the growth rate even when taking into account the supersample covariance, while the reconstruction cannot correct for the field variation of the supersample modes.

We study the mutual relationship between dark matter-electron scattering experiments and possible new dark matter substructure nearby hinted by the Gaia data. We show how kinematic substructure could affect the average and modulation spectra of dark matter-electron scattering in semiconductors and the discovery reaches of future experiments with these targets. Conversely, we demonstrate how future data could probe and constrain the fraction of dark matter in substructure, even when it constitutes a subdominant component of the local dark matter density.

The inert doublet model is a minimal dark matter model with strong theoretical motivations, where the stability of dark matter is usually achieved by imposing a $Z_2$ parity. We promote the $Z_2$ parity into a global $U(1)$ symmetry and study its phenomenological implications. There are two characteristic features of the model: both the $CP$-even and $CP$-odd neutral inert scalars, $h_1$ and $h_2$, become DM candidates; the number of model parameters is one less than that with $Z_2$ parity. We first analyze the constraints from LEP experiments, electroweak precision tests, theoretical stability, Higgs precision data, dark matter relic density, and direct detection experiments. It is found that if the model is required to explain at least 10% of the observed relic density, the theory is extremely limited such that the dark matter mass is about 70 GeV and the charged Higgs boson is not very heavy. Focusing on this narrow parameter space, we calculate the production cross sections of almost all the possible mono-$X$ and mono-$X{X}^{\prime }$ processes at the LHC. The mono-$W\gamma$ process is shown to have high discovery potential with the help of the decay of the intermediate-mass charged Higgs boson into $W^{\pm }{h}_{1,2}$. A search strategy is designed to increase the potential discovery of the model for the mono-$W\gamma$ signal at both the HL-LHC and the FCC-hh. The optimal cut on $E_T^{\mathrm{miss}}/\sqrt{H_T}$ is suggested to maximize the signal significance, being about 0.76 at the HL-LHC and about 7.5 at the FCC-hh.

If there is Lorentz symmetry violation in the $t$ quark sector of the standard model, changes to particles’ dispersion relations might allow for the existence of stable top-flavored hadrons. Observations of the survival of high-energy $\gamma$-rays over astrophysical distances can be used to place constraints on Lorentz violation coefficients in the $t$ sector at $\sim {10}^{-4}–{10}^{-6}$ levels of precision.

We explore a class of models which can provide a common origin for the recently observed evidence for lepton flavor universality violation in $b\to s{l}^{+}{l}^{-}$ decays, the dark matter (DM) problem, and the long-standing muon ($g-2$) anomaly. In particular, both anomalies in the $B$ meson decays and the muon ($g-2$) can be explained by the additional one-loop diagrams with DM candidates. We first classify several simple models according to the new fields’ quantum numbers. We then focus on a specific promising model and perform a detailed study of both DM and flavor physics. A random scan over the relevant parameter space reveals that there is indeed a large parameter space which can explain the three new physics phenomena simultaneously, while satisfying all other flavor and DM constraints. Finally, we discuss some of the possible new physics signatures at the Large Hadron Collider.

We report progress toward computing the heavy quark momentum diffusion coefficient from the correlator of two chromoelectric fields attached to a Polyakov loop in pure SU(3) gauge theory. Using a multilevel algorithm and tree-level improvement, we study the behavior of the diffusion coefficient as a function of temperature in the wide range $1.1<T/T_{\mathrm{c}}<{10}^4$ in order to compare it to perturbative expansions at high temperature. We find that within errors, the lattice results are remarkably compatible with the next-to-leading-order perturbative result.

We investigate an effective flavor-symmetric Yang-Mills-Higgs model with $N^2-1$ adjoint scalar fields. We find a set of Bogomol’nyi-Prasad-Sommerfield equations that provide vortex solutions and calculate their energies for arbitrary representations. We show that, for a given $N$-ality $k$, the energy of the corresponding antisymmetric representation is the lowest. This completes the proof that this model is able to reproduce a Casimir law for the string tension at asymptotic distances.

We consider a triangle diagram for $B^0\to (J/\psi {\pi }^{+}{\pi }^{-})K^{+}{\pi }^{-}$ where an $X(3872)$ peak has been observed experimentally. We demonstrate that a triangle singularity inherent in the triangle diagram creates a sharp peak in the $J/\psi {\pi }^{+}{\pi }^{-}$ invariant mass distribution when the final $(J/\psi {\pi }^{+}{\pi }^{-})\pi$ invariant mass is at and around the $D^{*}{\overline{D}}^{*}$ threshold. The position and width of the peak are 3871.68 MeV (a few keV above the $D^{*0}{\overline{D}}^0$ threshold) and $\sim 0.4\mathrm{MeV}$, respectively, in perfect agreement with the precisely measured $X(3872)$ mass and width: $3871.69\pm 0.17\mathrm{MeV}$ and $<1.2\mathrm{MeV}$. This remarkable agreement is virtually parameter-free. The result indicates that the considered mechanism has to be understood in advance when separating an $X(3872)$-pole contribution from $B^0\to (J/\psi {\pi }^{+}{\pi }^{-})K^{+}{\pi }^{-}$ data; the separation yields an $X(3872)\pi$ line shape that could be used to determine the $X(3872)$ mass. We suggest a method to set a constraint on the triangle mechanism by analyzing a charge analogous process $B^0\to (J/\psi {\pi }^0{\pi }^{-})K^{+}{\pi }^0$ where a similar triangle singularity generates an $X^{-}(3876)$-like peak.

We develop the spectroscopy of $c\overline{c}c\overline{c}$ and other all-heavy tetraquark states in the dynamical diquark model. In the most minimal form of the model (e.g., each diquark appears only in the color-triplet combination; the nonorbital spin couplings connect only quarks within each diquark), the spectroscopy is extremely simple. Namely, the $S$-wave multiplets contain precisely three degenerate states ($0^{++}$, $1^{+-}$, $2^{++}$) and the seven $P$-wave states satisfy an equal-spacing rule when the tensor coupling is negligible. When comparing numerically to the recent LHCb results, we find the best interpretation is assigning $X(6900)$ to the $2S$ multiplet, while a lower state suggested at about 6740 MeV fits well with the members of the $1P$ multiplet. We also predict the location of other multiplets ($1S$, $1D$, etc.) and discuss the significance of the $cc$ open-flavor threshold.

We present a search for an excess of neutrino interactions due to dark matter in the form of weakly interacting massive particles (WIMPs) annihilating in the Galactic center or halo based on the data set of Super-Kamiokande-I, -II, -III and -IV taken from 1996 to 2016. We model the neutrino flux, energy, and flavor distributions assuming WIMP self-annihilation is dominant to $\nu \overline{\nu }$, ${\mu }^{+}{\mu }^{-}$, $b\overline{b}$, or $W^{+}{W}^{-}$. The excess is in comparison to atmospheric neutrino interactions which are modeled in detail and fit to data. Limits on the self-annihilation cross section $⟨{\sigma }_{A}V⟩$ are derived for WIMP masses in the range 1 GeV to 10 TeV, reaching as low as $9.6\times {10}^{-23}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ for 5 GeV WIMPs in $b\overline{b}$ mode and $1.2\times {10}^{-24}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ for 1 GeV WIMPs in $\nu \overline{\nu }$ mode. The obtained sensitivity of the Super-Kamiokande detector to WIMP masses below several tens of GeV is the best among similar indirect searches to date.

We observe that in presence of excitation, a thermodynamic Smarr-like relation corresponding to a generalized entanglement temperature ($T_g$) can be holographically obtained for the entanglement entropy of a subsystem. Such a relation emerges naturally by demanding that the generalized entanglement temperature produces the exact Hawking temperature as the leading term in the IR limit ($l\to \infty$). Remarkably, this relation has the same form as the Smarr relation in black hole thermodynamics. We demonstrate this for three spacetime geometries, namely, a background with a nonconformal factor, a hyperscaling violating geometry background, and a charged black hole background which corresponds to a field theory with a finite chemical potential.