In the expanding universe, two interacting fields are no longer in thermal contact when the interaction rate becomes smaller than the Hubble expansion rate. After decoupling, two subsystems are usually treated separately in accordance with equilibrium thermodynamics and the thermodynamic entropy gives a fiducial quantity conserved in each subsystem. In this paper, we discuss a correction to this paradigm from quantum entanglement of two coupled fields. The thermodynamic entropy is generalized to the entanglement entropy. We formulate a perturbation theory to derive the entanglement entropy and present Feynman rules in diagrammatic calculations. For specific models to illustrate our formulation, an interacting scalar-scalar system, quantum electrodynamics, and the Yukawa theory are considered. We calculate the entanglement entropy in these models and find a quantum correction to the thermodynamic entropy. The correction is revealed to be important in circumstances of instantaneous decoupling.

We study the cosmological effects of adding terms of higher order in the usual energy-momentum tensor to the matter Lagrangian of general relativity. This is in contrast to most studies of higher-order gravity which focus on generalizing the Einstein-Hilbert curvature contribution to the Lagrangian. The resulting cosmological theories give rise to field equations of similar form to several particular theories with different fundamental bases, including bulk viscous cosmology, loop quantum gravity, $k$-essence, and brane-world cosmologies. We find a range of exact solutions for isotropic universes, discuss their behaviors with reference to the early- and late-time evolution, accelerated expansion, and the occurrence or avoidance of singularities. We briefly discuss extensions to anisotropic cosmologies and delineate the situations where the higher-order matter terms will dominate over anisotropies on approach to cosmological singularities.

The vector leptoquark representation, $U_{\mu }=(3,1,2/3)$, was recently identified as an exceptional single mediator model to address experimental hints on lepton flavor universality violation in semileptonic $B$-meson decays, both in neutral ($b\to s\mu \mu$) and charged ($b\to c\tau \nu$) current processes. Nonetheless, it is well known that massive vectors crave an ultraviolet (UV) completion. We present the first full-fledged UV complete and calculable gauge model which incorporates this scenario while remaining in agreement with all other indirect flavor and electroweak precision measurements, as well as, direct searches at high-$p_T$. The model is based on a new non-Abelian gauge group spontaneously broken at the TeV scale, and a specific flavor structure suppressing flavour violation in $\mathrm{\Delta }F=2$ processes while inducing sizeable semileptonic transitions.

In most multicomponent dark-matter scenarios, two classes of processes generically contribute to event rates at experiments capable of probing the nature of the dark sector. The first class consists of “diagonal” processes involving only a single species of dark-matter particle—processes analogous to those which arise in single-component dark-matter scenarios. By contrast, the second class consists of “off-diagonal” processes involving dark-matter particles of different species. Such processes include inelastic scattering at direct-detection experiments, asymmetric production at colliders, dark-matter co-annihilation, and certain kinds of dark-matter decay. In typical multicomponent scenarios, the contributions from diagonal processes dominate over those from off-diagonal processes. Unfortunately, this tends to mask those features which are most sensitive to the multicomponent nature of the dark sector. In this paper, by contrast, we point out that there exist natural, multicomponent dark-sector scenarios in which the off-diagonal contributions actually dominate over the diagonal. This then gives rise to a new, enhanced picture of dark-matter complementarity. In this paper, we introduce a scenario in which this situation arises and examine the enhanced picture of dark-matter complementarity which emerges.

We present a theoretical study of the $\gamma \gamma \to \pi \eta$ process from the threshold up to 1.4 GeV in the $\pi \eta$ invariant mass. For the s-wave $a_0(980)$ resonance state we adopt a dispersive formalism using a coupled-channel Omnès representation, while the d-wave $a_2(1320)$ state is described as a Breit-Wigner resonance. An analytic continuation to the $a_0(980)$ pole position allows us to extract its two-photon decay width as ${\mathrm{\Gamma }}_{a_0\to \gamma \gamma }=0.27(4)\mathrm{keV}$.

We have studied the mass spectra of the hidden-charm/bottom $qc\overline{q}\overline{c}$, $sc\overline{s}\overline{c}$ and $qb\overline{q}\overline{b}$, $sb\overline{s}\overline{b}$ tetraquark states with $J^{PC}=0^{++}$ and $2^{++}$ in the framework of QCD sum rules. We construct ten scalar and four tensor interpolating currents in a systematic way and calculate the mass spectra for these tetraquark states. The $X^{*}(3860)$ may be either an isoscalar tetraquark state or ${\chi }_{c0}(2P)$. If the $X^{*}(3860)$ is a tetraquark candidate, our results prefer the $0^{++}$ option over the $2^{++}$ one. The $X(4160)$ may be classified as either the scalar or tensor $qc\overline{q}\overline{c}$ tetraquark state, while the $X(3915)$ favors a $0^{++}qc\overline{q}\overline{c}$ or $sc\overline{s}\overline{c}$ tetraquark assignment over the tensor one. The $X(4350)$ cannot be interpreted as a $sc\overline{s}\overline{c}$ tetraquark with either $J^{PC}=0^{++}$ or $2^{++}$.

We investigate graviton radiation in gravitational scattering at small impact parameters $b<R\equiv 2G\sqrt{s}$ and extreme energies $s\gg M_P^2$, a regime in which classical collapse is thought to occur, and thus radiation may be suppressed also. Here however, by analyzing the soft-based representation of radiation recently proposed in the semiclassical Amati-Ciafaloni-Veneziano framework, we argue that gravitons can be efficiently produced in the untrapped region $|\mathit{x}|\gtrsim R>b$, so as to suggest a possible completion of the unitarity sum. In fact, such energy radiation at large distances turns out to compensate and to gradually reduce to nothing the amount of energy $E^{\prime }$ being trapped at small-$b$’s, by thus avoiding the quantum tunneling suppression of the elastic scattering and suggesting a unitary evolution. We finally look at the coherent radiation sample so obtained and we find that, by energy conservation, it develops an exponential frequency damping corresponding to a “quasitemperature” of order $\hslash /R$, which is naturally related to a Hawking radiation and is suggestive of a black-hole signal at quantum level.

In the present work, we investigate evolving wormhole configurations described by a constant redshift function in Einstein-Cartan theory. The matter content consists of a Weyssenhoff fluid along with an anisotropic matter which together generalize the anisotropic energy momentum tensor in general relativity in order to include the effects of intrinsic angular momentum (spin) of particles. Using a generalized Friedmann-Robertson-Walker spacetime, we derive analytical evolving wormhole geometries by assuming a particular equation of state for energy density and pressure profiles. We introduce exact asymptotically flat and anti–de Sitter spacetimes that admit traversable wormholes and respect energy conditions throughout the spacetime. The rate of expansion of these evolving wormholes is determined only by the Friedmann equation in the presence of spin effects.

We explore the use of the galaxy bispectrum induced by the nonlinear gravitational evolution as a possible probe to test general scalar-tensor theories with second-order equations of motion. We find that time dependence of the leading second-order kernel is approximately characterized by one parameter, the second-order index, which is expected to trace the higher-order growth history of the Universe. We show that our new parameter can significantly carry new information about the nonlinear growth of structure. We forecast future constraints on the second-order index as well as the equation-of-state parameter and the growth index.

We present numerical measurements of the power spectrum response function of the gravitational growth of cosmic structures, defined as the functional derivative of the nonlinear spectrum with respect to the linear counterpart, based on 1400 cosmological simulations. We develop a simple analytical model based on a regularization of the standard perturbative calculation. Using the model prediction, we show that this function gives a natural way to interpolate the nonlinear power spectrum over cosmological parameter space from single- or multistep interpolations. We demonstrate that once an accurate numerical spectrum template is available for one (or a small number of) cosmological model(s), it doubles the range in $k$ for which percent-level accuracy can be obtained even for a large change in the cosmological parameters. The Python package RESPRESSO we developed to make those predictions is publicly available.

The nature of the $\gamma$-ray emission from the Fermi bubbles is unknown. Both hadronic and leptonic models have been formulated to explain the peculiar $\gamma$-ray signal observed by the Fermi-LAT between 0.1–500 GeV. If this emission continues above $\sim 30\mathrm{TeV}$, hadronic models of the Fermi bubbles would provide a significant contribution to the high-energy neutrino flux detected by the IceCube observatory. Even in models where leptonic $\gamma$-rays produce the Fermi bubbles flux at GeV energies, a hadronic component may be observable at very high energies. The combination of IceCube and HAWC measurements have the ability to distinguish these scenarios through a comparison of the neutrino and $\gamma$-ray fluxes at a similar energy scale. We examine the most recent four-year data set produced by the IceCube Collaboration and find no evidence for neutrino emission originating from the Fermi bubbles. In particular, we find that previously suggested excesses are consistent with the diffuse astrophysical background with a p-value of 0.22 (0.05 in an extreme scenario that all the IceCube events that overlap with the bubbles come from them). Moreover, we show that existing and upcoming HAWC observations provide independent constraints on any neutrino emission from the Fermi bubbles due to the close correlation between the $\gamma$-ray and neutrino fluxes in hadronic interactions. The combination of these results disfavors a significant contribution from the Fermi bubbles to the IceCube neutrino flux.

Under conditions prevailing in certain classes of compact astrophysical systems, the active magnetosphere of a rotating black hole becomes charge starved, giving rise to the formation of a spark gap in which plasma is continuously produced. The plasma production process is accompanied by curvature and inverse Compton emission of gamma rays in the GeV–TeV band, which may be detectable by current and future experiments. The properties of the gap emission have been studied recently using a fully general-relativistic model of a local steady gap. However, this model requires artificial adjustment of the electric current which is determined, in reality, by the global properties of the magnetosphere. In this paper we map the parameter regime in which steady gap solutions exist, using a steady-state gap model in Kerr geometry, and show that such solutions are allowed only under restrictive conditions that may not apply to most astrophysical systems. We further argue that even the allowed solutions are inconsistent with the global magnetospheric structure. We conclude that magnetospheric gaps are inherently intermittent, and point out that this may drastically change their emission properties.

We examine the top squark (stop) and gluino reach of the proposed 33 TeV energy upgrade of the Large Hadron Collider (LHC33) in the Minimal Supersymmetric Standard Model (MSSM) with light Higgsinos and relatively heavy electroweak gauginos. In our analysis, we assume that stops decay to Higgsinos via ${\tilde{t}}_1\to t{\tilde{Z}}_1$, ${\tilde{t}}_1\to t{\tilde{Z}}_2$, and ${\tilde{t}}_1\to b{\tilde{W}}_1$ with branching fractions in the ratio $1:1:2$ (expected if the decay occurs dominantly via the superpotential Yukawa coupling), while gluinos decay via $\tilde{g}\to t{\tilde{t}}_1$ or via three-body decays to third-generation quarks plus Higgsinos. These decay patterns are motivated by models of natural supersymmetry where Higgsinos are expected to be close in mass to $m_Z$, but gluinos may be as heavy as 5–6 TeV, and stops may have masses up to $\sim 3\mathrm{TeV}$. We devise cuts to optimize the signals from stop and gluino pair production at LHC33. We find that experiments at LHC33 should be able to discover stops with $>5\sigma$ significance if $m_{{\tilde{t}}_1}<2.3$ (2.8) [3.2] TeV for an integrated luminosity of 0.3 (1) $[3]{\mathrm{ab}}^{-1}$. The corresponding reach for gluinos extends to 5 (5.5) [6] TeV. These results imply that experiments at LHC33 should be able to discover at least one of the stop or gluino pair signals even with an integrated luminosity of $0.3{\mathrm{ab}}^{-1}$ for natural supersymmetry models with no worse than 3% electroweak fine-tuning and quite likely both gluinos and stops for an integrated luminosity of $3{\mathrm{ab}}^{-1}$.

We study Dirac fermionic dark matter (DM, ${\chi }^0$) and confront it with recent data. To evade the stringent direct search limits from PandaX-II, XENON1T, and LUX experiments, the quantum numbers of the Dirac DM are taken to be $I_3=Y=0$ to remove the tree-level $Z$-exchange diagram. Loop amplitudes can contribute to the elastic scattering cross section. We find that there are cancellations in the one-loop diagrams, which largely reduce the cross section and make the Dirac DM viable in the direct search. For a generic isospin $I$, we survey the Dirac DM mass constrained by the latest results of PandaX-II, XENON1T, and LUX experiments, the observed DM relic density, and the H.E.S.S. and the Fermi-LAT astrophysical observations. Sommerfeld enhancement effects on DM annihilation processes are investigated. We find that the cross section of ${\chi }^0{\overline{\chi }}^0$ annihilating to the standard model gauge bosons are in general significantly enhanced, and the Fermi-LAT, the H.E.S.S. upper limits on $⟨\sigma v⟩(W^{+}{W}^{-},\gamma \gamma )$, and the observed relic density become serious constraints on the Dirac DM mass. The $I<4$ cases are ruled out, and for $I\ge 4$, the lower bounds on the Dirac DM mass are forced to be $\gtrsim 60\mathrm{TeV}$. The elastic scattering cross section for $m_{\chi }$ of a few tens of TeV with a generic $I$ is found to be ${\sigma }^{SI}\simeq I^2(I+1{)}^2\times 7\times {10}^{-49}{\mathrm{cm}}^2$. The predicted $⟨\sigma ({\chi }^0{\overline{\chi }}^0\to Z^0{Z}^0,Z^0\gamma ,\gamma \gamma )v⟩$ and ${\sigma }^{SI}$ are sizable, and they will be useful to search for DM in astrophysical observation and in a direct search in the near future.

Studies of the reaction $\gamma \pi \to \pi \pi$, in the context of the ongoing Primakoff program of the COMPASS experiment at CERN, give access to the radiative couplings of the $\rho (770)$ and ${\rho }_3(1690)$ resonances. We provide a vector-meson-dominance estimate of the respective radiative width of the ${\rho }_3$, ${\mathrm{\Gamma }}_{{\rho }_3\to \pi \gamma }=48(18)\mathrm{keV}$, as well as its impact on the $F$-wave in $\gamma \pi \to \pi \pi$. For the $\rho (770)$, we establish the formalism necessary to extract its radiative coupling directly from the residue of the resonance pole by analytic continuation of the $\gamma \pi \to \pi \pi$ amplitude to the second Riemann sheet, without any reference to the vector-meson-dominance hypothesis.

We exploit a conjectured continuity between super Yang-Mills on ${\mathbb{R}}^3\times {\mathbb{S}}^1$ and pure Yang-Mills to study $k$-strings in the latter theory. As expected, we find that Wilson-loop correlation functions depend on the N-ality of a representation $\mathcal{R}$ to the leading order. However, the next-to-leading order correction is not universal and is given by the group characters, in the representation $\mathcal{R}$, of the permutation group. We also study W-bosons in super Yang-Mills. We show that they are deconfined on the string world sheet, and therefore, they can change neither the string N-ality nor its tension. This phenomenon mirrors the fact that soft gluons do not screen probe charges with nonzero N-ality in pure Yang-Mills. Finally, we comment on the scaling law of $k$-strings in super Yang-Mills and compare our findings with strings in Seiberg-Witten theory, deformed Yang-Mills theory, and holographic studies that were performed in the ’t Hooft large-$N$ limit.

Assuming that the pion-pion scattering amplitude and its absorptive part are analytic inside an ellipse in the complex $t$ plane with foci $t=0$, $u=0$ and right extremity $t=4m_{\pi }^2+\epsilon$, ($\epsilon >0$)—except for cuts prescribed by the Mandelstam representation for $t\ge 4m_{\pi }^2$, $u\ge 4m_{\pi }^2$, and bounded by $s^N$ on the boundary of this domain—we prove that for $s\to \infty$, ${\sigma }_{\mathrm{inel}}(s)>\frac{\text{const}}{s^{5/2}}\exp [-\frac{\sqrt{s}}{4}(N+5/2)\ln s].$

This work deals with form factors of the energy-momentum tensor (EMT) of spin-0 particles and the unknown particle property $D$ term related to the EMT, and it is divided into three parts. The first part explores free, weakly and strongly interacting theories to study EMT form factors with the following findings. (i) The free Klein-Gordon theory predicts for the $D$ term $D=-1$. (ii) Even infinitesimally small interactions can drastically impact $D$. (iii) In strongly interacting theories one can encounter large negative $D$ though notable exceptions exist, which include Goldstone bosons of chiral symmetry breaking. (iv) Contrary to common belief one cannot arbitrarily add “total derivatives” to the EMT. Rather the EMT must be defined in an unambiguous way. The second part deals with the interpretation of the information content of EMT form factors in terms of 3D densities with the following results. (i) The 3D-density formalism is internally consistent. (ii) The description is subject to relativistic corrections but those are acceptably small in phenomenologically relevant situations including nucleons and nuclei. (iii) The free-field result $D=-1$ persists when a spin-0 boson is not pointlike but “heuristically given some internal structure.” The third part investigates the question of whether such “giving of an extended structure” can be implemented dynamically, and it has the following insights. (i) We construct a consistent microscopic theory which, in a certain parametric limit, interpolates between extended and pointlike solutions. (ii) This theory is exactly solvable which is rare in $3+1$ dimensions, admits nontopological solitons of $Q$-ball type, and has a Gaussian field amplitude. (iii) The interaction of this theory belongs to a class of logarithmic potentials which were discussed in the literature, albeit in different contexts including beyond-standard-model phenomenology, cosmology, and Higgs physics.

The bipartite entanglement entropy of a segment of length $l$ in $1+1$-dimensional conformal field theories (CFT) follows the formula $S=\frac{c}{3}\ln l+\gamma$, where $c$ is the central charge of the CFT and $\gamma$ is a cutoff-dependent constant which diverges in the absence of an ultraviolet cutoff. According to this formula, systems with larger central charges have more bipartite entanglement entropy. Using quantum Fisher information (QFI), we argue that systems with bigger central charges not only have larger bipartite entanglement entropy, but also have more multipartite entanglement content. In particular, we argue that since a system with a smaller smallest scaling dimension has a larger QFI, the multipartite entanglement content of a CFT is dependent on the value of the smallest scaling dimension present in the spectrum of the system. We show that our argument seems to be consistent with some of the existing results regarding the von Neumann entropy, negativity, and localizable entanglement in $1+1$ dimensions. Furthermore, we also argue that the QFI decays under renormalization group flow between two unitary CFTs. Finally, we also comment on nonconformal but scale-invariant systems.