We consider light propagation in a nonmagnetized pressureless plasma around a Kerr black hole. We find the necessary and sufficient condition the plasma electron density has to satisfy to guarantee that the Hamilton-Jacobi equation for the light rays is separable, i.e., that a generalized Carter constant exists. For all cases where this condition is satisfied we determine the photon region; i.e., the region in the spacetime where spherical light rays exist. A spherical light ray is a light ray that stays on a sphere $r=\text{constant}$ (in Boyer-Lindquist coordinates). Based on these results, we calculate the shadow of a Kerr black hole under the influence of a plasma that satisfies the separability condition. More precisely, we derive an analytical formula for the boundary curve of the shadow on the sky of an observer that is located anywhere in the domain of outer communication. Several examples are worked out.

We calculate the leading order in ${\alpha }_s$ QCD amplitude for exclusive neutrino and antineutrino production of a $D$ pseudoscalar charmed meson on an unpolarized nucleon. We work in the framework of the collinear QCD approach, where generalized parton distributions (GPDs) factorize from perturbatively calculable coefficient functions. We include both $O(m_c)$ terms in the coefficient functions and $O(M_D)$ mass term contributions in the heavy meson distribution amplitudes. We emphasize the sensitivity of specific observables on the transversity quark GPDs.

Since the discovery of the Higgs boson at the Large Hadron Collider, a future electron-position collider has been proposed for precisely studying its properties. We investigate the production of the Higgs boson at such an $e^{+}{e}^{-}$ collider associated with a $Z$ boson, and calculate for the first time the mixed QCD-electroweak corrections to the total cross sections. We provide an approximate analytic formula for the cross section and show that it reproduces the exact numeric results rather well for collider energies up to 350 GeV. We also provide numeric results for $\sqrt{s}=500\mathrm{GeV}$, where the approximate formula is no longer valid. We find that the $\mathcal{O}(\alpha {\alpha }_s)$ corrections amount to a 1.3% increase of the cross section for a center-of-mass energy around 240 GeV. This is significantly larger than the expected experimental accuracy and has to be included for extracting the properties of the Higgs boson from the measurements of the cross sections in the future.

Deep inelastic scattering of very-high-energy neutrinos can potentially be enhanced by the production of a single top quark or charm quark via the interaction of a virtual $W$-boson exchange with a $b$-quark or $s$-quark parton in the nucleon. The single top contribution shows a sharp rise at neutrino energies above 0.5 PeV and gives a cross section contribution of order 5% at 10 PeV, while single charm has a low-energy threshold and contributes about 25%. Semileptonic decays of top and charm give dimuon events of which the kinematic characteristics are shown. The angular separation of the dimuons from heavy-quark production in the IceCube detector can reach up to 1 deg. Top-quark production has a unique, but rare, three muon signal.

We compute the Wald entropy of the Schwarzschild black hole in the ghost-free, infinite-derivative gravity that is quadratic in curvature. This is not given purely by the area law but includes an additional contribution depending on the power of the d’Alembertian operator, when requiring that the massless graviton be the only propagating mode in the Minkowski spacetime.

We derive the classical null energy condition, understood as a constraint on the Ricci tensor, from the second law of thermodynamics applied locally to Bekenstein-Hawking entropy associated with patches of null congruences. The derivation provides evidence that the null energy condition, which has usually been regarded as a condition on matter, is fundamentally a property of gravity.

Einstein’s weak equivalence principle (WEP) states that any freely falling, uncharged test particle follows the same identical trajectory independent of its internal structure and composition. Since the polarization of a photon is considered to be part of its internal structure, we propose that polarized photons from astrophysical transients, such as gamma-ray bursts (GRBs) and fast radio bursts (FRBs), can be used to constrain the accuracy of the WEP through the Shapiro time delay effect. Assuming that the arrival time delays of photons with different polarizations are mainly attributed to the gravitational potential of the Laniakea supercluster of galaxies, we show that a strict upper limit on the differences of the parametrized post-Newtonian parameter $\gamma$ value for the polarized optical emission of GRB 120308A is $\mathrm{\Delta }\gamma <1.2\times {10}^{-10}$, for the polarized gamma-ray emission of GRB 100826A is $\mathrm{\Delta }\gamma <1.2\times {10}^{-10}$, and for the polarized radio emission of FRB 150807 is $\mathrm{\Delta }\gamma <2.2\times {10}^{-16}$. These are the first direct verifications of the WEP for multiband photons with different polarizations. In particular, the result from FRB 150807 provides the most stringent limit to date on a deviation from the WEP, improving by one order of magnitude the previous best result based on Crab pulsar photons with different energies.

We investigate the production and absorption of $Z_b(10610)$ and $Z_b^{\prime }(10650)$ states in a hadronic medium, via the processes ${\overline{B}}^{(*)}{B}^{(*)}\to \pi Z_b^{(\prime )}$ and the corresponding inverses reactions. We use effective field Lagrangians based on an $SU(4)$ extension of the hidden gauge formalism to account for the couplings between light and heavy mesons, and a phenomenological Lagrangian involving the $B^{*}{B}^{(*)}{Z}_b^{(\prime )}$ vertices. The absorption cross sections are found to be much larger than the production ones.

Motivated by the absence of signals of new physics in searches for both new particles at the LHC and a weakly interacting massive particle dark matter candidate, we consider a scenario where supersymmetry is broken at a scale above the reheating temperature. The low-energy particle content then only consists of Standard Model states and a gravitino. We investigate the possibility that the latter provides the main component of dark matter through the annihilation of thermalized Standard Model particles. We focus on the case where its production through scattering in the thermal plasma is well approximated by the nonlinear supersymmetric effective Lagrangian of the associated Goldstino and identify the parameter space allowed by the cosmological constraints, allowing the possibility of a large reheating temperature compatible with leptogenesis scenarios and alleviating the so-called “gravitino problem”.

In this work we study canonical gravity in finite regions for which we introduce a generalization of the Gibbons-Hawking boundary term including the Immirzi parameter. We study the canonical formulation on a spacelike hypersurface with a boundary sphere and show how the presence of this term leads to an unprecedented type of degrees of freedom coming from the restoration of the gauge and diffeomorphism symmetry at the boundary. In the presence of a loop quantum gravity state, these boundary degrees of freedom localize along a set of punctures on the boundary sphere. We demonstrate that these degrees of freedom are effectively described by auxiliary strings with a three-dimensional internal target space attached to each puncture. We show that the string currents represent the local frame field, that the string angular momenta represent the area flux, and that the string stress tensor represents the two-dimensional metric on the boundary of the region of interest. Finally, we show that the commutators of these broken diffeomorphism charges of quantum geometry satisfy, at each puncture, a Virasoro algebra with central charge $c=3$. This leads to a description of the boundary degrees of freedom in terms of a CFT structure with central charge proportional to the number of loop punctures. The boundary $SU(2)$ gauge symmetry is recovered via the action of the $U(1{)}^3$ Kac-Moody generators (associated with the string current) in a way that is the exact analog of an infinite dimensional generalization of the Schwinger spin representation. We finally show that this symmetry is broken by the presence of background curvature.

The beyond-generalized Proca theories are the extension of second-order massive vector-tensor theories (dubbed generalized Proca theories) with two transverse vector modes and one longitudinal scalar besides two tensor polarizations. Even with this extension, the propagating degrees of freedom remain unchanged on the isotropic cosmological background without an Ostrogradski instability. We study the cosmology in beyond-generalized Proca theories by paying particular attention to the dynamics of late-time cosmic acceleration and resulting observational consequences. We derive conditions for avoiding ghosts and instabilities of tensor, vector, and scalar perturbations and discuss viable parameter spaces in concrete models allowing the dark energy equation of state smaller than $-1$. The propagation speeds of those perturbations are subject to modifications beyond the domain of generalized Proca theories. There is a mixing between scalar and matter sound speeds, but such a mixing is suppressed during most of the cosmic expansion history without causing a new instability. On the other hand, we find that derivative interactions arising in beyond-generalized Proca theories give rise to important modifications to the cosmic growth history. The growth rate of matter perturbations can be compatible with the redshift-space distortion data due to the realization of gravitational interaction weaker than that in generalized Proca theories. Thus, it is possible to distinguish the dark energy model in beyond-generalized Proca theories from the counterpart in generalized Proca theories as well as from the $\mathrm{\Lambda }\mathrm{CDM}$ model.

After the discovery of extraterrestrial high-energy neutrinos, the next major goal of neutrino telescopes will be identifying astrophysical objects that produce them. The flux of the brightest source $F_{\max }$, however, cannot be probed by studying the diffuse neutrino intensity. We aim at constraining $F_{\max }$ by adopting a broken power-law flux distribution, a hypothesis supported by observed properties of any generic astrophysical sources. The first estimate of $F_{\max }$ comes from the fact that we can only observe one universe and, hence, the expected number of sources above $F_{\max }$ cannot be too small compared with one. For abundant source classes such as starburst galaxies, this one-source constraint yields a value of $F_{\max }$ that is an order of magnitude lower than the current upper limits from point-source searches. Then we derive upper limits on $F_{\max }$ assuming that the angular power spectrum is still consistent with neutrino shot noise. We find that the limits obtained with upgoing muon neutrinos in IceCube can already be quite competitive, especially for rare but bright source populations such as blazars. The limits will improve nearly quadratically with exposure and, therefore, be even more powerful for the next generation of neutrino telescopes.

We propose a new application of single molecule magnet crystals: their use as “magnetic bubble chambers” for the direct detection of sub-GeV dark matter. The spins in these macroscopic crystals effectively act as independent nanoscale magnets. When antialigned with an external magnetic field they form metastable states with a relaxation time that can be very long at sufficiently low temperatures. The Zeeman energy stored in this system can be released through localized heating, caused for example by the scattering or absorption of dark matter, resulting in a spin avalanche (or “magnetic deflagration”) that amplifies the effects of the initial heat deposit, enabling detection. Much like the temperature and pressure in a conventional bubble chamber, the temperature and external magnetic field set the detection threshold for a single molecule magnet crystal. We discuss this detector concept for dark matter detection and propose ways to ameliorate backgrounds. If successfully developed, this detector concept can search for hidden photon dark matter in the meV–eV mass range with sensitivities exceeding current bounds by several orders of magnitude.

We study the charmless two-body decays of $b$ baryons (${\mathrm{\Lambda }}_b$, ${\mathrm{\Xi }}_b^{-}$, ${\mathrm{\Xi }}_b^0$). We find that $\mathcal{B}({\mathrm{\Xi }}_b^{-}\to \mathrm{\Lambda }{\rho }^{-})=(2.08_{-0.51}^{+0.69})\times {10}^{-6}$ and $\mathcal{B}({\mathrm{\Xi }}_b^0\to {\mathrm{\Sigma }}^{+}{M}^{-})=(4.45_{-1.09}^{+1.46},11.49_{-2.9}^{+3.8},4.69_{-0.79}^{+1.11},2.98_{-0.51}^{+0.76})\times {10}^{-6}$ for $M^{-}=({\pi }^{-},{\rho }^{-},K^{-},K^{*-})$, which are compatible with $\mathcal{B}({\mathrm{\Lambda }}_b\to p{\pi }^{-},p{K}^{-})$. We also obtain that $\mathcal{B}({\mathrm{\Lambda }}_b\to \mathrm{\Lambda }\omega )=(2.30\pm 0.10)\times {10}^{-6}$, $\mathcal{B}({\mathrm{\Xi }}_b^{-}\to {\mathrm{\Xi }}^{-}\varphi ,{\mathrm{\Xi }}^{-}\omega )\simeq \mathcal{B}({\mathrm{\Xi }}_b^0\to {\mathrm{\Xi }}^0\varphi ,{\mathrm{\Xi }}^0\omega )=(5.35\pm 0.41,3.65\pm 0.16)\times {10}^{-6}$ and $\mathcal{B}({\mathrm{\Xi }}_b^{-}\to {\mathrm{\Xi }}^{-}{\eta }^{(\prime )})\simeq \mathcal{B}({\mathrm{\Xi }}_b^0\to {\mathrm{\Xi }}^0{\eta }^{(\prime )})=(2.51_{-0.46}^{+0.70},2.99_{-0.57}^{+1.16})\times {10}^{-6}$. For the $CP$-violating asymmetries, we show that ${\mathcal{A}}_{CP}({\mathrm{\Lambda }}_b\to p{K}^{*-})={\mathcal{A}}_{CP}({\mathrm{\Xi }}_b^{-}\to {\mathrm{\Sigma }}^0(\mathrm{\Lambda })K^{*-})={\mathcal{A}}_{CP}({\mathrm{\Xi }}_b^0\to {\mathrm{\Sigma }}^{+}{K}^{*-})=(19.7\pm 1.4)\%$. Similar to the charmless two-body ${\mathrm{\Lambda }}_b$ decays, the ${\mathrm{\Xi }}_b$ decays are accessible to the LHCb detector.

We report the first measurement of the fraction of $J/\psi$ mesons coming from $B$-meson decay ($F_{B\to J/\psi }$) in $p+p$ collisions at $\sqrt{s}=510\mathrm{GeV}$. The measurement is performed using the forward silicon vertex detector and central vertex detector at PHENIX, which provide precise tracking and distance-of-closest-approach determinations, enabling the statistical separation of $J/\psi$ due to $B$-meson decays from prompt $J/\psi$. The measured value of $F_{B\to J/\psi }$ is $8.1\%\pm 2.3\%(\text{stat})\pm 1.9\%(\text{syst})$ for $J/\psi$ with transverse momenta $0<p_T<5\mathrm{GeV}/c$ and rapidity $1.2<|y|<2.2$. The measured fraction $F_{B\to J/\psi }$ at PHENIX is compared to values measured by other experiments at higher center of mass energies and to fixed-order-next-to-leading-logarithm and color-evaporation-model predictions. The $b\overline{b}$ cross section per unit rapidity [$d\sigma /dy(pp\to b\overline{b})$] extracted from the obtained $F_{B\to J/\psi }$ and the PHENIX inclusive $J/\psi$ cross section measured at 200 GeV scaled with color-evaporation-model calculations, at the mean $B$ hadron rapidity $y=\pm 1.7$ in 510 GeV $p+p$ collisions, is $3.63_{-1.70}^{+1.92}\mu \mathrm{b}$. It is consistent with the fixed-order-next-to-leading-logarithm calculations.

The chiral kinetic theory of Weyl fermions with collisions in the presence of weak electric and magnetic fields is derived from quantum field theories. It is found that the side-jump terms in the perturbative solution of Wigner functions play a significant role for the derivation. Moreover, such terms manifest the breaking of Lorentz symmetry for distribution functions. The Lorentz covariance of Wigner functions thus leads to modified Lorentz transformation associated with side-jump phenomena further influenced by background fields and collisions.

The interpolation from supersymmetric to nonsupersymmetric heterotic theories is studied, via the Scherk-Schwarz compactification of supersymmetric $6D$ theories to $4D$. A general modular-invariant Scherk-Schwarz deformation is deduced from the properties of the $6D$ theories at the endpoints, which significantly extends previously known examples. This wider class of nonsupersymmetric $4D$ theories opens up new possibilities for model building. The full one-loop cosmological constant of such theories is studied as a function of compactification radius for a number of cases, and the following interpolating configurations are found: two supersymmetric $6D$ theories related by a $T$-duality transformation, with intermediate $4D$ maximum or minimum at the string scale; a nonsupersymmetric $6D$ theory interpolating to a supersymmetric $6D$ theory, with the $4D$ theory possibly having an anti–de Sitter minimum; and a “metastable” nonsupersymmetric $6D$ theory interpolating via a $4D$ theory to a supersymmetric $6D$ theory.

Strongly interacting matter in the form of nuggets of nuclear-density material is not currently excluded as a dark matter candidate in the ten gram to hundreds of kilogram mass range. A recent variation on quark nugget dark matter models postulates that a first-order imbalance between matter and antimatter at the quark-gluon phase transition in the early Universe could lead to most of the dark matter bound into heavy (baryon number $B\sim 10^{25}$) antiquark nuggets in the current epoch, explaining both the dark matter preponderance and the matter-antimatter asymmetry. Interactions of these massive objects with normal matter in the Earth and Sun lead to annihilation and an associated neutrino flux in the $\sim 30\mathrm{MeV}$ range. We calculate these fluxes for antiquark nuggets of sufficient flux to account for the dark matter and find that current neutrino flux limits from Super-Kamiokande (SuperK) exclude these objects as major dark matter candidates at a high confidence level. Antiquark nuggets in the previously allowed mass range cannot account for more than $\sim 15\%$ of the dark matter flux.

The paper develops high-order physical-constraint-preserving (PCP) methods for general relativistic hydrodynamic (GRHD) equations, equipped with a general equation of state. Here the physical constraints, describing the admissible states of GRHD, are referred to the subluminal constraint on the fluid velocity and the positivity of the density, pressure and specific internal energy. Preserving these constraints is very important for robust computations, otherwise violating one of them will lead to the ill-posed problem and numerical instability. To overcome the difficulties arising from the inherent strong nonlinearity contained in the constraints, we derive an equivalent definition of the admissible states. Using this definition, we prove the convexity, scaling invariance and Lax-Friedrichs (LxF) splitting property of the admissible state set $\mathcal{G}$, and discover the dependence of $\mathcal{G}$ on the spacetime metric. Unfortunately, such dependence yields the nonequivalence of $\mathcal{G}$ at different points in curved spacetime, and invalidates the convexity of $\mathcal{G}$ in analyzing PCP schemes. This obstacle is effectively overcame by introducing a new formulation of the GRHD equations. Based on this formulation and the above theories, a first-order LxF scheme is designed on general unstructured mesh and rigorously proved to be PCP under a Courant-Friedrichs-Lewy (CFL) condition. With two types of PCP limiting procedures, we design high-order, provably (not probably) PCP methods under discretization on the proposed new formulation. These high-order methods include the PCP finite difference, finite volume and discontinuous Galerkin methods.

We evaluate the pion-nucleon intermediate-state contribution to the two-photon exchange (TPE) correction in the elastic electron-nucleon scattering within a dispersive framework. We calculate the contribution from all $\pi N$ partial waves using the MAID parametrization. We provide the corresponding TPE correction to the unpolarized $ep$ scattering cross section in the region of low momentum transfer $Q^2\lesssim 0.064{\mathrm{GeV}}^2$, where no analytical continuation into the unphysical region of the TPE scattering amplitudes is required. We compare our result in the forward angular region with an alternative TPE calculation, in terms of structure functions, and find a good agreement, indicating a small contribution at low $Q^2$ due to discontinuities beyond $\pi N$. We also compare our results with empirical fits.