We study the time delay between successive relativistic images in gravitational lensing as a possible discriminator between various collapse end states and hence as a probe of cosmic censorship. Specifically we consider both black hole and naked singularity spacetimes admitting photon spheres where an infinite number of relativistic Einstein rings can be formed at almost the same radius and naked singularity spacetimes without a photon sphere where multiple relativistic Einstein rings can form almost up to the center of the lens. The metrics we have considered to sample these scenarios are the Schwarzschild black hole, Janis-Newman-Winicour (naked singularity with photon sphere), Joshi-Malfarina-Narayan, and Tolman-VI (naked singularities without photon sphere) which are a fair sample of the theoretical possibilities. We show that the differential time delay between the relativistic images for naked singularities without a photon sphere progressively decreases for the models we study as opposed to that for black holes and naked singularities with a photon sphere, where it is known to be roughly constant. This characteristic difference in the time delay between successive images for these two cases can be potentially exploited for a source with known intrinsic variability to discriminate between these scenarios even when the images are not spatially resolved.

We study a nonthermal scenario in a two-Higgs doublet extension of the standard model (SM), augmented by a $U(1{)}_{\mathrm{B}-\mathrm{L}}$ gauge symmetry. In this setup, it is shown that the decay product of a weakly coupled scalar field just above the electroweak scale can generate visible and dark matter (DM) simultaneously. DM is unstable because of the broken $B-L$ symmetry. The lifetime of DM ($\approx 5\times {10}^{25}\sec$) is found to be much longer than the age of the Universe, and its decay to the SM leptons at the present epoch can explain the positron excess observed at the AMS-02. The relic abundance and the direct detection constraint from Xenon-100 can rule out a large parameter space, just leaving the $B-L$ breaking scale around $\approx 2–4\mathrm{TeV}$.

In this paper, using matching method in the probe limit, we investigate some properties of a holographic superconductor in Gauss-Bonnet gravity with Born-Infeld electrodynamics. We discuss the effects of the Gauss-Bonnet coupling $\alpha$ and the Born-Infeld parameter $b$ on the critical temperature and condensate. We find that both $\alpha$ and $b$ make the critical temperature decrease, which makes it more difficult for the condensate to form. Moreover we study the magnetic effect on the holographic superconductor and obtain that the ratio between the critical magnetic field and the square of the critical temperature increases from zero as the temperature is lowered below the critical value $T_c$, which agrees well with previous results. We also find that the critical magnetic field is indeed affected by the Gauss-Bonnet coupling, but not by the Born-Infeld parameter.

We present a conjecture on the complete spectrum of single-trace operators in the infinite $N$ limit of $W_N$ minimal model and evidence for the conjecture. We further propose that the holographic dual of $W_N$ minimal model in the ’t Hooft limit is an unusual “semilocal” higher spin gauge theory on ${\mathrm{AdS}}_3\times S^1$. At each point on the $S^1$ lives a copy of three-dimensional Vasiliev theory, that contains an infinite tower of higher spin gauge fields coupled to a single massive complex scalar propagating in ${\mathrm{AdS}}_3$. The Vasiliev theories at different points on the $S^1$ are correlated only through the ${\mathrm{AdS}}_3$ boundary conditions on the massive scalars. All but one single tower of higher spin symmetries are broken by the boundary conditions.

In this article, we exhibit explicitly the matrix model ($\theta =\infty$) fixed point of ${\varphi }^4$ theory on noncommutative spacetime with only two noncommuting directions, using the Wilson renormalization group recursion formula and the $1/N$ expansion of the zero-dimensional reduction, and then calculate the mass critical exponent $\nu$ and the anomalous dimension $\eta$ in various dimensions.

We study quantum dissipative effects due to the accelerated motion of a single, imperfect, zero-width mirror. It is assumed that the microscopic degrees of freedom on the mirror are confined to it, like in plasma or graphene sheets. Therefore, the mirror is described by a vacuum polarization tensor ${\Pi }_{\alpha \beta }$ concentrated on a time-dependent surface. Under certain assumptions about the microscopic model for the mirror, we obtain a rather general expression for the Euclidean effective action, a functional of the time-dependent mirror’s position, in terms of two invariants that characterize the tensor ${\Pi }_{\alpha \beta }$. The final result can be written in terms of the TE and TM reflection coefficients of the mirror, with qualitatively different contributions coming from them. We apply that general expression to derive the imaginary part of the “in-out” effective action, which measures dissipative effects induced by the mirror’s motion, in different models, in particular for an accelerated graphene sheet.

This manuscript reports the first order $\beta$-functions of recently proved just renormalizable random tensor models endowed with a $U(1{)}^d$ gauge invariance. The models that we consider are polynomial Abelian ${\phi }_6^4$ and ${\phi }_5^6$ models. We show in this work that both models are asymptotically free in the UV.

We consider an expanding relativistic fluid with spherical symmetry as a model for an analog Friedmann-Robertson-Walker (FRW) spacetime. In the framework of relativistic acoustic geometry we demonstrate how to mimic an arbitrary FRW spacetime with positive, zero, or negative spatial curvature. In the Lagrangian description we show that a particular FRW spacetime is obtained by choosing the appropriate potential. We discuss several examples and in particular the analog de Sitter spacetime in the coordinate representation with positive and negative spatial curvature.

The quantum-reduced loop-gravity technique has been introduced for dealing with cosmological models. We show that it can be applied rather generically: any time the spatial metric can be gauge fixed to a diagonal form. The technique selects states based on reduced graphs with Livine-Speziale coherent intertwiners and could simplify the analysis of the dynamics in the full theory.

We illustrate a framework for constructing models of chaotic inflation where the inflaton is the position of a D3-brane along the universal cover of a string compactification. In our scenario, a brane rolls many times around a nontrivial one-cycle, thereby unwinding a Ramond-Ramond flux. These “flux monodromies” are similar in spirit to the monodromies of Silverstein, Westphal, and McAllister, and their four-dimensional description is that of Kaloper and Sorbo. Assuming moduli stabilization is rigid enough, the large-field inflationary potential is protected from radiative corrections by a discrete shift symmetry.

The spectral distortion of the cosmic microwave background blackbody spectrum in a radially inhomogeneous space-time, designed to exactly reproduce a $\Lambda \mathrm{CDM}$ expansion history along the past light cone, is shown to exceed the upper bound established by COBE-FIRAS by a factor of approximately 3700. This simple observational test helps uncover a slew of pathological features that lie hidden inside the past light cone, including a radially contracting phase at decoupling and, if followed to its logical extreme, a naked singularity at the radially inhomogeneous big bang.

Following the way proposed recently by Hernandez and Smirnov, we seek possible residual symmetries in the quark sector with a focus on the von Dyck groups. We begin with two extreme cases in which both ${\theta }_{13}$ and ${\theta }_{23}$ or only ${\theta }_{13}$ are set to zero. Then, cases where all the Cabibbo-Kobayashi-Maskawa parameters are allowed to take nonzero values are explored. The $Z_7$ symmetry is favorable to realize only the Cabibbo angle. On the other hand, larger groups are necessary in order to be consistent with all the mixing parameters. Possibilities of embedding the obtained residual symmetries into the $\Delta (6N^2)$ series are also briefly discussed.

In a previous article Don Bennett and I looked for, found, and proposed a game in which the standard model gauge group $S(U(2)\times U(3))$ gets singled out as the “winner.” This “game” means that the by Nature chosen gauge group should be just the one that has the maximal value for a quantity, which is a modification of the ratio of the quadratic Casimir for the adjoint representation and that for a “smallest” faithful representation. Here I propose to extend this “game” to construct a corresponding game between different potential dimensions for space-time. The idea is to formulate how the same competition as the one between the potential gauge groups would run out, if restricted to the potential Lorentz or Poincare groups achievable for different dimensions of space-time $d$. The remarkable point is that it is the experimental space-time dimension 4 which wins. So the same function defined over Lie groups seems to single out both the gauge group and the dimension of space-time in nature. This seems a rather strange coincidence, unless there really is some similar physical reason behind causing our game-variable (or goal variable) to be selected to be maximal. It has crudely to do with that the groups preferred are easily represented on very “small” but yet faithful representations.

Strongly modified $h\gamma \gamma$ and $hgg$ couplings indicate new electroweak and color mediators, respectively, with a light mass and a significant coupling to the Higgs boson. We point out the Higgs boson could have a significant decay width into the mediators. This represents one new class of exotic Higgs decay possibilities: off-shell exotic Higgs decays. We then propose uncovering the hidden new physics through such exotic decays. A great advantage of this strategy is that we can directly probe the couplings between the Higgs boson and the mediators, which is hard to achieve by using other methods. Focusing on the electroweak mediators, we study a simplified model using as an example final states with tau leptons and neutrinos. Because one of the mediators is off shell and its decay products are extremely soft, it is challenging to make a discovery at the Large Hadron Collider. A Higgs factory such as the International Linear Collider, however, could serve as a discovery machine for such exotic Higgs decays even in an early stage.

We analyze the phenomenological implications of introducing vector-like leptons on the Higgs sector in the Higgs triplet model. We impose only a parity symmetry which disallows mixing between the new states and the ordinary leptons. If the vector leptons are allowed to be relatively light, they enhance or suppress the decay rates of loop-dominated neutral Higgs boson decays $h\to \gamma \gamma$ and $h\to Z\gamma$, and affect their correlation. An important consequence is that, for light vector leptons, the decay patterns of the the doubly charged Higgs boson will be altered, modifying the restrictions on their masses. We study the implications for signals at the LHC, for both $\sqrt{s}=7\mathrm{TeV}$ and for 13 TeV, and show that doubly charged boson decays into same-sign vector leptons could be observed.