Naturalness arguments imply the existence of higgsinos lighter than 200–300 GeV. However, because these higgsinos are nearly mass degenerate, they release very little visible energy in their decays, and (even putting aside triggering issues) signals from electroweak higgsino pair production typically remain buried under Standard Model backgrounds. Prospects for detecting higgsino pair production via events with monojets or monophotons from initial state radiation are also bleak because of signal-to-background rates typically at the 1% level. Here, we consider the possibility of reducing backgrounds by requiring the presence of soft daughter leptons from higgsino decays in monojet events. We find that LHC14 experiments with an integrated luminosity of $300{\mathrm{fb}}^{-1}$ should be sensitive to light higgsinos at the $5\sigma$ level for $\mu <170\mathrm{GeV}$ with a $S/B\sim 8.5\%$. For an integrated luminosity of $1000{\mathrm{fb}}^{-1}$ (which should be possible at a high-luminosity LHC) the corresponding sensitivity to $\mu$ extends to over 200 GeV though the systematic uncertainty would have to be controlled to considerably better than 5%. The corresponding reach from measurements of the rate asymmetry between monojet events with same flavor vs opposite flavor dileptons is $\sim 10–15\mathrm{GeV}$ smaller, but does not suffer the systematic uncertainty from the normalization of the background.

Using a constituent quark model, we study possible molecular structures in the nonstrange open-charm and open-bottom spectrum. $D^{(*)}N$, ${\overline{B}}^{(*)}N$, $D^{(*)}\mathrm{\Delta }$, and ${\overline{B}}^{(*)}\mathrm{\Delta }$ configurations are considered. We found molecular structures in all these channels. In particular, we describe the ${\mathrm{\Lambda }}_c(2940)$ as a $D^{*}N$ molecule with $J^P={\frac{3}{2}}^{-}$, whereas $D^{(*)}\mathrm{\Delta }$ structures may be an option for the recently discovered $X_c(3250)$ and $X_c(3212)$ resonances.

We revisit the large instanton contribution to the gluon Pauli form factor of the constituent quark noted by Kochelev. We check that it contributes sizably to the single spin asymmetry in polarized $p_{\uparrow }p\to \pi X$. We use it to predict a large double spin asymmetry in doubly polarized $p_{\uparrow }{p}_{\uparrow }\to \pi \pi X$.

We study the cocktail model in which the Majorana neutrino masses are generated by the so-called “cocktail” three-loop diagrams with the dark matter particle running in the loops. In particular, we give the analytic expressions of the neutrino masses in the model by the detailed calculation of the cocktail diagrams. Based on the numerical calculation of the loop integrals, we explore the parameter space which can give the correct orders of neutrino masses while satisfying other experimental constraints, such as those from the neutrinoless double beta decay, low-energy lepton flavor violation processes, electroweak precision tests, and collider searches. As a result, the large couplings and the large mass difference between the two singly charged (neutral) scalars are required.

We present the observation of doubly produced $J/\psi$ mesons with the D0 detector at Fermilab in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. The production cross section for both singly and doubly produced $J/\psi$ mesons is measured using a sample with an integrated luminosity of $8.1{\mathrm{fb}}^{-1}$. For the first time, the double $J/\psi$ production cross section is separated into contributions due to single and double parton scatterings. Using these measurements, we determine the effective cross section ${\sigma }_{\text{eff}}$, a parameter characterizing an effective spatial area of the parton-parton interactions and related to the parton spatial density inside the nucleon.

We discuss the role of gravitational corrections to the running of the electric charge through the evaluation of scattering amplitudes of charged particles in massless scalar electrodynamics. Computing the complete divergent part of the $S$-matrix amplitude for two distinct scattering processes, we show that quantum gravitational corrections do not alter the running behavior of the electric charge. Our result does not exclude the possibility that the presence of a second dimensional constant in the model (a cosmological constant or the presence of massive particles) could alter this behavior, as was proposed in earlier works.

Event horizons are (generically) not physically observable. In contrast, apparent horizons (and the closely related trapping horizons) are generically physically observable—in the sense that they can be detected by observers working in finite-size regions of spacetime. Consequently event horizons are inappropriate tools for defining astrophysical black holes, or indeed for defining any notion of an evolving black hole (evolving either due to accretion or Hawking radiation). The only situation in which an event horizon becomes physically observable is for the very highly idealized stationary or static black holes, when the event horizon is a Killing horizon which is degenerate with the apparent and trapping horizons, and then it is the physical observability of the apparent/trapping horizons that is fundamental—the event horizon merely comes along for the ride.

We study the consequences of the presence of a boundary in topological field theories in various dimensions. We characterize, univocally and on very general grounds, the field content and the symmetries of the actions which live on the boundary. We then show that these actions are covariant, despite appearances. We show also that physically relevant theories like the 2D Luttinger liquid model or the four-dimensional Maxwell theory, can be seen as boundary reductions of higher-dimensional topological field theories, which do not display local observables.

The cosmic blackbody background radiation pervades the entire Universe, and so falls into every astrophysical black hole. The blueshift of the infalling photons, measured by a static observer, is infinite at the event horizon. This raises a question as to whether a “firewall” of high energy density may form just outside the horizon, or whether the effect can be attributed exclusively to a singular behavior of the static observer’s frame at the horizon. In principle, the presence of such a firewall may alter the motion of the infalling matter, influence the black hole evolution, or even invalidate the vacuum Einstein field equation solution as a realistic approximation for black holes. In this paper we show by means of analytic calculations that all these effects indeed exist, but their magnitude is typically negligibly small, even though the matter stress tensor is divergent in the static frame at $r=2M$. That is not surprising because of the divergent relation of that frame to a freely falling frame as $r\to 2M$; however, it represents a kind of classical analogue for the black hole complementarity principle that has been proposed for quantum effects near a black hole. What is perhaps more surprising is the divergence of the radiation stress tensor for massive particles moving on circular geodesic orbits for values of $r$ approaching $r=3M$. However such orbits will not occur for infalling matter in realistic accretion discs.

Though individual stellar parameters of compact stars usually demonstrate obvious dependence on the equation of state (EOS), EOS-insensitive universal formulas relating these parameters remarkably exist. In the present paper, we explore the interrelationship between two such formulas, namely the $f$-$I$ relation connecting the $f$-mode quadrupole oscillation frequency ${\omega }_2$ and the moment of inertia $I$, and the $I$-Love-$Q$ relations relating $I$, the quadrupole tidal deformability ${\lambda }_2$, and the quadrupole moment $Q$, which have been proposed by Lau, Leung, and Lin [Astrophys. J. 714, 1234 (2010)] and Yagi and Yunes [Science 341, 365 (2013)], respectively. A relativistic universal relation between ${\omega }_l$ and ${\lambda }_l$ with the same angular momentum $l=2,3,\dots$, the so-called “diagonal $f$-Love relation” that holds for realistic compact stars and stiff polytropic stars, is unveiled here. An in-depth investigation in the Newtonian limit is further carried out to pinpoint its underlying physical mechanism and hence leads to a unified $f$-$I$-Love relation. We reach the conclusion that these EOS-insensitive formulas stem from a common physical origin—compact stars can be considered as quasiincompressible when they react to slow time variations introduced by $f$-mode oscillations, tidal forces and rotations.

We argue that the effective theory describing the long-wavelength dynamics of black branes is the same effective theory that describes the dynamics of biophysical membranes. We improve the phase structure of higher-dimensional black rings by considering finite thickness corrections in this effective theory, showing a striking agreement between our analytical results and recent numerical constructions while simultaneously drawing a parallel between gravity and the effective theory of biophysical membranes.

We present results from a new code for computing gravitational perturbations of the Kerr geometry. This new code carefully maintains high precision to allow us to obtain high-accuracy solutions for the gravitational quasinormal modes of the Kerr space-time. Part of this new code is an implementation of a spectral method for solving the angular Teukolsky equation that, to our knowledge, has not been used before for determining quasinormal modes. We focus our attention on two main areas. First, we explore the behavior of these quasinormal modes in the extreme limit of Kerr, where the frequency of certain modes approaches accumulation points on the real axis. We compare our results with recent analytic predictions of the behavior of these modes near the accumulation points and find good agreement. Second, we explore the behavior of solutions of modes that approach the special frequency $M\omega =-2i$ in the Schwarzschild limit. Our high-accuracy methods allow us to more closely approach the Schwarzschild limit than was possible with previous numerical studies. Unlike previous work, we find excellent agreement with analytic predictions of the behavior near this special frequency. We include a detailed description of our methods, and make use of the theory of confluent Heun differential equations throughout. In particular, we make use of confluent Heun polynomials to help shed some light on the controversy of the existence, or not, of quasinormal and total-transmission modes at certain special frequencies in the Schwarzschild limit.

We study the falloff behavior of test electromagnetic fields in higher dimensions as one approaches infinity along a congruence of “expanding” null geodesics. The considered backgrounds are Einstein spacetimes including, in particular, (asymptotically) flat and (anti-)de Sitter spacetimes. Various possible boundary conditions result in different characteristic falloffs, in which the leading component can be of any algebraic type (N, II, or G). In particular, the peeling-off of radiative fields $F=N{r}^{1-n/2}+G{r}^{-n/2}+\dots$ differs from the standard four-dimensional one (instead, it qualitatively resembles the recently determined behavior of the Weyl tensor in higher dimensions). General $p$-form fields are also briefly discussed. In even $n$ dimensions, the special case $p=n/2$ displays unique properties and peels off in the “standard way” as $F=N{r}^{1-n/2}+II{r}^{-n/2}+\dots$. A few explicit examples are mentioned.

We consider perturbations of a static and spherically symmetric background endowed with a metric tensor and a scalar field in the framework of the effective field theory of modified gravity. We employ the previously developed $2+1+1$ canonical formalism of a double Arnowitt-Deser-Misner (ADM) decomposition of space-time, which singles out both time and radial directions. Our building block is a general gravitational action that depends on scalar quantities constructed from the $2+1+1$ canonical variables and the lapse. Variation of the action up to first order in perturbations gives rise to three independent background equations of motion, as expected from spherical symmetry. The dynamical equations of linear perturbations follow from the second-order Lagrangian after a suitable gauge fixing. We derive conditions for the avoidance of ghosts and Laplacian instabilities for the odd-type perturbations. We show that our results not only incorporate those derived in the most general scalar-tensor theories with second-order equations of motion (the Horndeski theories) but they can be applied to more generic theories beyond Horndeski.

We develop a nonsingular bouncing cosmology using a nontrivial coupling of general relativity to fermionic fields. The usual big bang singularity is avoided thanks to a negative energy density contribution from the fermions. Our theory is ghost free since the fermionic operator that generates the bounce is equivalent to torsion, which has no kinetic terms. The physical system consists of standard general relativity plus a topological sector for gravity and fermionic matter described by Dirac fields with a nonminimal coupling. We show that a scale-invariant power spectrum generated in the contracting phase can be recovered by suitable choices of fermion number density and bare mass, thus providing a possible alternative to the inflationary scenario.

We consider the vacuum energy of massive quantum fields in an expanding universe. We define a conserved renormalized energy-momentum tensor by means of a comoving cutoff regularization. Using exact solutions for de Sitter space-time, we show that in a certain range of mass and renormalization scales there is a contribution to the vacuum energy density that scales as nonrelativistic matter and that such a contribution becomes dominant at late times. By means of the WKB approximation, we find that these results can be extended to arbitrary Robertson-Walker geometries. We study the range of parameters in which the vacuum energy density would be compatible with current limits on dark matter abundance. Finally, by calculating the vacuum energy in a perturbed Robertson-Walker background, we obtain the speed of sound of density perturbations and show that the vacuum energy density contrast can grow on sub-Hubble scales as in standard cold dark matter scenarios.

In our previous paper [K. Feng, T. Qiu, and Y.-S. Piao, Phys. Lett. B 729, 99 (2014)], we have shown a curvaton model where the curvaton has a nonminimal derivative coupling to gravity. Such a coupling could cause scale invariance of the perturbations for a wide range of constant values of the equation of state of the cosmic background at the early time. In this paper, we continue our study by fully analyzing its perturbations up to the third order. Apart from the usual 2-point correlation function that have already been calculated in Feng, Qiu, and Piao [Phys. Lett. B 729, 99 (2014)], we also take into account the 3-point correlation functions, including the pure scalar part, the pure tensor part, and the cross-correlations between scalar and tensor perturbation modes. We find that for the pure scalar part, the 3-point correlation functions can generate non-Gaussianities that fit the PLANCK data very well. For the pure tensor and mixed parts, the shape functions have peaks at squeezed and equilateral limits, respectively, responsible for sizable $f_{\mathrm{NL}}^{\text{sqz}}$ and $f_{\mathrm{NL}}^{\mathrm{eql}}$, which could be tested by the future observational data.

We compute the second-order density fluctuation in the proper-time hypersurface of nonrelativistic matter flows and relate it to galaxy number density fluctuation, providing physical grounds for galaxy bias in the context of general relativity. At the linear order, the density fluctuation in the proper-time hypersurface is equivalent to the density fluctuation in the comoving synchronous gauge, in which two separate gauge conditions coincide. However, at the second order, the density fluctuations in these gauge conditions differ, while both gauge conditions represent the same proper-time hypersurface. Compared to the density fluctuation in the temporal comoving and spatial $C$-gauge conditions, the density fluctuation in the commonly used gauge condition ($N=1$ and $N^{\alpha }=0$) violates the mass conservation at the second order. We provide their physical interpretations in each gauge condition by solving the geodesic equation and the nonlinear evolution equations of nonrelativistic matter. We apply this finding to the second-order galaxy biasing in general relativity, which complements the second-order relativistic description of galaxy clustering in Yoo and Zaldarriaga [Phys. Rev. D 90, 023513, (2014)].

We continue our exploration of the nearly Peccei-Quinn symmetric limit shared by common singlet extensions of the minimal supersymmetric standard model. This limit has been established as a viable framework for studying subelectroweak scale dark matter phenomenology and has interesting and direct connections to new exotic Higgs decay physics. We present analytic calculations to motivate the important phenomenological features mentioned above. We also discuss benchmark points in this model framework that accommodate the observed Galactic center gamma-ray excess. We emphasize connections between phenomenology of dark matter direct detection and indirect detection, and new exotic decay channels for the 125 GeV Higgs boson. We conclude by identifying two benchmark modes of exotic Higgs decays for $h\to {\tau }^{+}{\tau }^{-}{\cancel{E}}_{\mathrm{T}}$ and $h\to b\overline{b}{\cancel{E}}_{\mathrm{T}}$ final states and estimate their sensitivity prospects at the LHC.

The production of electron-positron pairs from the quantum vacuum polarized by the superposition of a strong and a perturbative oscillating electric field mode is studied. Our outcomes rely on a nonequilibrium quantum field theoretical approach, described by the quantum kinetic Boltzmann-Vlasov equation. By superimposing the perturbative mode, the characteristic resonant effects and Rabi-like frequencies in the single-particle distribution function are modified, as compared to the predictions resulting from the case driven by a strong oscillating field mode only. This is demonstrated in the momentum spectra of the produced pairs. Moreover, the dependence of the total number of pairs on the intensity parameter of each mode is discussed and a strong enhancement found for large values of the relative Keldysh parameter.