Recently, deviations in flavor observables of $\overline{B}\to D^{(*)}\tau \overline{\nu }$ have been shown between the predictions in the Standard Model and the experimental results reported by BABAR, Belle, and LHCb collaborations. One of the solutions to this anomaly is obtained in a class of leptoquark model with a scalar leptoquark boson $S_1$, which is a $SU(3{)}_c$ triplet and $SU(2{)}_L$ singlet particle with $-1/3$ hypercharge interacting with a quark-lepton pair. With well-adjusted couplings, this model can explain the anomaly and be compatible with all flavor constraints. In such a case, the $S_1$ boson can be pair-produced at CERN’s Large Hadron Collider (LHC) and subsequently decay as $S_1^{*}\to t\tau$, $b{\nu }_{\tau }$, and $c\tau$. This paper explores the current 8 and 13 TeV constraints, as well as the detailed prospects at 14 TeV, of this flavor-motivated $S_1$ model. From the current available 8 and 13 TeV LHC searches, we obtain constraints on the $S_1$ boson mass for $M_{S_1}<400–640\mathrm{GeV}$ depending on values of the leptoquark couplings to fermions. Then we study future prospects for this scenario at the 14 TeV LHC using detailed cut analyses and evaluate exclusion and discovery potentials for the flavor-motivated $S_1$ leptoquark model from searches for the $(b\nu )(\overline{b}\overline{\nu })$ and $(c\tau )(\overline{c}\overline{\tau })$ final states. In the latter case, we consider several scenarios for the identification of charm jets. As a result, we find that the $S_1$ leptoquark origin of the $\overline{B}\to D^{(*)}\tau \overline{\nu }$ anomaly can be probed with $M_{S_1}\lesssim 600/800\mathrm{GeV}$ at the 14 TeV LHC with $\mathcal{L}=300/3000{\mathrm{fb}}^{-1}$ of accumulated data. One can also see that the 14 TeV LHC run II with $\mathcal{L}=300{\mathrm{fb}}^{-1}$ can exclude the $S_1$ leptoquark boson up to $M_{S_1}\sim 0.8\mathrm{TeV}$ at 95% confidence level, whereas a future 14 TeV LHC with $\mathcal{L}=3000{\mathrm{fb}}^{-1}$ data has a potential to discover the $S_1$ leptoquark boson with its mass up to $M_{S_1}\sim 1.1\mathrm{TeV}$ with over $5\sigma$ significance, from the $(b\nu )(\overline{b}\overline{\nu })$ and/or $(c\tau )(\overline{c}\overline{\tau })$ searches.

Recently, the LHCb collaboration reported the observation of the decay mode $B_c^{-}\to {\overline{B}}_s^0{\pi }^{-}$ with the largest exclusive branching fraction amongst the known decay modes of all the $B$ mesons. Here we propose a search for a few lepton-number violating ($\mathrm{\Delta }L=2$) decay modes of $B_c$ which can only be induced by Majorana neutrinos. Distinguishing between Dirac and Majorana nature of neutrinos is an outstanding problem and hence, all possible searches for Majorana neutrinos need to be carried out. Since the lepton number violating modes are expected to be rare, when using meson decay modes for these searches one expects CKM favored modes to be the preferred ones; $B_c\to B_s$ is one such transition. With a resonance enhancement of the Majorana neutrino mediating the $B_c^{-}\to {\overline{B}}_s^0{\ell }_1^{-}{\ell }_2^{-}{\pi }^{+}$ modes one can hope to observe these rare modes, or, even their nonobservation can be used to obtain tight constraints on the mixing angles of the heavy Majorana singlet with the light flavour neutrinos from upper limits of the branching fractions. Using these modes we obtain exclusion curves for the mixing angles which are tighter or compatible with results from earlier studies. However, we find that the relatively suppressed mode $B_c^{-}\to J/\psi {\ell }_1^{-}{\ell }_2^{-}{\pi }^{+}$ can provide even tighter constraints on $|V_{eN}{|}^2$, $|V_{\mu N}{|}^2$, $|V_{eN}{V}_{\mu N}|$, and in a larger range of the heavy neutrino mass. Further, exclusion regions for $|V_{eN}{V}_{\tau N}|$, $|V_{\mu N}{V}_{\tau N}|$ can also be obtained for masses larger than those accessible in tau decays. Upper limits on $\mathcal{B}(B_c^{-}\to {\pi }^{+}{\ell }_1^{-}{\ell }_2^{-})$ can also result in stringent exclusion curves for all the mixing elements, including that for $|V_{\tau N}{|}^2$ in a mass range where it is unconstrained thus far.

We investigate the random motion of a mirror in ($1+1$)-dimensions that is immersed in a thermal bath of massless scalar particles which are interacting with the mirror through a boundary condition. Imposing the Dirichlet or the Neumann boundary conditions on the moving mirror, we evaluate the mean radiation reaction force on the mirror and the correlation function describing the fluctuations in the force about the mean value. From the correlation function thus obtained, we explicitly establish the fluctuation-dissipation theorem governing the moving mirror. Using the fluctuation-dissipation theorem, we compute the mean-squared displacement of the mirror at finite and zero temperature. We clarify a few points concerning the various limiting behavior of the mean-squared displacement of the mirror. While we recover the standard result at finite temperature, we find that the mirror diffuses logarithmically at zero temperature, confirming similar conclusions that have been arrived at earlier in this context. We also comment on a subtlety concerning the comparison between zero temperature limit of the finite temperature result and the exact zero temperature result.

Continuing the work of Honda [Phys. Rev. Lett. 116, 211601 (2016)], we study the perturbative series in general 3d $\mathcal{N}=2$ supersymmetric Chern-Simons matter theory with $U(1{)}_R$ symmetry, which is given by a power series expansion of inverse Chern-Simons levels. We find that the perturbative series is usually non-Borel summable along a positive real axis for various observables. Alternatively, we prove that the perturbative series is always Borel summable along a negative (positive) imaginary axis for positive (negative) Chern-Simons levels. It turns out that the Borel resummations along this direction are the same as the exact results and, therefore, are correct ways of resumming the perturbative series.

We evaluate quantum effects due to a two-component Dirac field in $2+1$ spacetime dimensions, coupled to domain-wall-like defects with a smooth shape. We show that these effects induce nontrivial contributions to the (shape-dependent) energy of the domain walls. For a single defect, we study the divergences in the corresponding self-energy, and also consider the role of the massless zero mode—corresponding to the Callan-Harvey mechanism—by coupling the Dirac field to an external gauge field. For two defects, we show that the Dirac field induces a nontrivial, Casimir-like effect between them, and we provide an exact expression for that interaction in the case of two straight-line parallel defects. As is the case for the Casimir interaction energy, the result is finite and unambiguous.

We obtain a class of regular black hole solutions in four-dimensional $f(R)$ gravity, $R$ being the curvature scalar, coupled to a nonlinear electromagnetic source. The metric formalism is used and static spherically symmetric spacetimes are assumed. The resulting $f(R)$ and nonlinear electrodynamics functions are characterized by a one-parameter family of solutions which are generalizations of known regular black holes in general relativity coupled to nonlinear electrodynamics. The related regular black holes of general relativity are recovered when the free parameter vanishes, in which case one has $f(R)\propto R$. We analyze the regularity of the solutions and also show that there are particular solutions that violate only the strong energy condition.

A conservative constraint on Einstein’s weak equivalence principle (WEP) can be obtained under the assumption that the observed time delay between correlated particles from astronomical sources is dominated by the gravitational fields through which they move. Current limits on the WEP are mainly based on the observed time delays of photons with different energies. It is highly desirable to develop more accurate tests that include the gravitational wave (GW) sector. The detection by the advanced LIGO/VIRGO systems of gravitational waves will provide attractive candidates for constraining the WEP, extending the tests to gravitational interactions with potentially higher accuracy. Considering the capabilities of the advanced LIGO/VIRGO network and the source direction uncertainty, we show that the joint detection of GWs and electromagnetic signals could probe the WEP to an accuracy down to ${10}^{-10}$, which is one order of magnitude tighter than previous limits, and 7 orders of magnitude tighter than the multimessenger (photons and neutrinos) results by supernova 1987A.

We study the existence of hairy black holes in the generalized Einstein-Skyrme model. It is proven that in the Bogomol’nyi-Prasad-Sommerfield model limit there are no hairy black hole solutions, although the model admits gravitating (and flat space) solitons. Furthermore, we find strong evidence that a necessary condition for the existence of black holes with Skyrmionic hair is the inclusion of the Skyrme term ${\mathcal{L}}_4$. As an example, we show that there are no hairy black holes in the ${\mathcal{L}}_2+{\mathcal{L}}_6+{\mathcal{L}}_0$ model and present a new kind of black hole solutions with compact Skyrmion hair in the ${\mathcal{L}}_4+{\mathcal{L}}_6+{\mathcal{L}}_0$ model.

We present a one-parameter family of exact solutions to Einstein’s equations that may be used to study the nature of the Green-Wald backreaction framework. Our explicit example is a family of Einstein-Rosen waves coupled to a massless scalar field. This solution may be reinterpreted as a generalized three-torus polarized Gowdy cosmology with scalar and gravitational waves. We use it to illustrate essential properties of the Green-Wald approach. Among other things we show that within our model the Green-Wald framework uniquely determines backreaction for finite-size inhomogeneities on a predefined background. The results agree with those calculated in the Charach-Malin approach. In the vacuum limit, the Green-Wald, the Charach-Malin and the Isaacson methods imply identical backreaction, as expected.

It has been recently suggested [Z. Berezhiani, A. D. Dolgov, and I. I. Tkachev, Phys. Rev. D 92, 061303 (2015)] that emerging tension between cosmological parameter values derived in high-redshift (CMB anisotropy) and low-redshift (cluster counts, Hubble constant) measurements can be reconciled in a model which contains a subdominant fraction of dark matter decaying after recombination. We check the model against the CMB Planck data. We find that lensing of the CMB anisotropies by the large-scale structure gives strong extra constraints on this model, limiting the fraction as $F<8\%$ at $2\sigma$ confidence level. However, investigating the combined data set of the CMB and conflicting low-$z$ measurements, we obtain that the model with $F\approx 2\%–5\%$ exhibits better fit (by $1.5–3\sigma$ depending on the lensing priors) compared to that of the concordance $\mathrm{\Lambda }\mathrm{CDM}$ cosmological model.

We propose a renormalizable model based on $\mathrm{\Delta }(27)$ family symmetry with an $SO(10)$ grand unified theory leading to a novel form of spontaneous geometrical $CP$ violation. The symmetries, including $\mathrm{\Delta }(27)$ and ${\mathbb{Z}}_9\times {\mathbb{Z}}_{12}\times {\mathbb{Z}}_4^R$, are broken close to the grand unified theory breaking scale to yield the minimal supersymmetric standard model with the standard $R$ parity. $SO(10)$ is broken via $SU(5)$ with doublet-triplet splitting achieved by a version of the Dimopoulos-Wilczek (missing vacuum expectation value) mechanism. Low-scale Yukawa structure is dictated by the coupling of matter to $\mathrm{\Delta }(27)$ antitriplets $\overline{\varphi }$ of which the vacuum expectation values are aligned in the constrained sequential dominance 3 directions by the superpotential. Light physical Majorana neutrinos masses emerge from a specific implementation of the seesaw mechanism within $SO(10)$. The model predicts a normal neutrino mass hierarchy with the best-fit lightest neutrino mass between 0.32 and 0.38 meV, $CP$-violating oscillation phase ${\delta }^l\approx (275–280)°$, and the remaining neutrino parameters all within $1\sigma$ of their best-fit experimental values.

Weakly coupled models for the 750 GeV diphoton resonance often invoke new particles carrying both color and/or electric charges to mediate loop-induced couplings of the resonance to two gluons and two photons. The new colored particles may not be stable and could decay into final states containing standard model particles. We consider an electroweak doublet of vectorlike quarks (VLQs) carrying electric charges of $5/3$ and $2/3$, respectively, which mediate the loop-induced couplings of the 750 GeV resonance. If the VLQ has a mass at around 1 TeV, it naturally gives rise to the observed diphoton signal strength while all couplings remain perturbative up to a high scale. At the same time, if the charge-$5/3$ VLQ decays into final states containing top quark and $W$ boson, it would contribute to the multilepton excesses observed in both run 1 and run 2 data. It is also possible to incorporate a dark matter candidate in the decay final states to explain the observed relic density.

It is by now established that neutrino oscillations occur due to nonzero masses and parameters in the leptonic mixing matrix. The extraction of oscillation parameters may be complicated due to subleading effects such as nonstandard neutrino interactions and one needs to have a fresh look how a particular parameter value is inferred from experimental data. In the present work, we focus on an important parameter entering the oscillation framework–the leptonic $CP$-violating phase $\delta$, about which we know very little. We demonstrate that the sensitivity to $CP$ violation gets significantly impacted due to nonstandard neutrino interaction effects for the upcoming long baseline experiment, Deep Underground Neutrino Experiment. We also draw a comparison with the sensitivities of other ongoing neutrino beam experiments such as $\mathrm{NO}\nu \mathrm{A}$ and T2K as well as a future generation experiment, T2HK.

We consider the signals arising from top partner pair production at the LHC as a probe of theories of neutral naturalness. We focus on scenarios in which top partners carry electroweak charges, such as folded supersymmetry or the quirky little Higgs. In this class of theories the top partners are pair produced as quirky bound states, since they are charged under a mirror color group whose lightest states are hidden glueballs. The quirks promptly de-excite and annihilate into glueballs, which decay back to Standard Model fermions via Higgs mixing. This can give rise to spectacular signatures at the LHC, such displaced decays, or high-multiplicity prompt production of many hard $\overline{b}b$ or ${\tau }^{+}{\tau }^{-}$ pairs. We show that signals arising from top partner pair production constitute the primary discovery channel for this class of theories in most regions of parameter space, and might provide the only experimental probe of scenarios with sub-cm glueball decay lengths. The measurement of top partner masses and couplings, which could be used to test the neutral naturalness mechanism directly, is also a tantalizing possibility.

We analytically consider the spontaneous formation of a fermionic crystalline geometry in a gravity background with Lifshitz scaling and/or hyperscaling violation. A fermionic vortex lattice solution sourced by the lowest Landau level has been obtained. Thermodynamic analysis shows that the fermionic vortex lattice favors an equilateral triangular configuration, regardless of the values of the Lifshitz scaling $z$ and the hyperscaling violation exponent $\theta$. Our results also show that the larger $z$ or lower $\theta$ leads to deeper minima in the free energy.

We study the time evolution of Wightman two-point functions of scalar fields in ${\mathrm{AdS}}_3$-Vaidya, a spacetime undergoing gravitational collapse. In the boundary field theory, the collapse corresponds to a quench process where the dual $1+1$-dimensional CFT is taken out of equilibrium and subsequently thermalizes. From the two-point function, we extract an effective occupation number in the boundary theory and study how it approaches the thermal Bose-Einstein distribution. We find that the Wightman functions, as well as the effective occupation numbers, thermalize with a rate set by the lowest quasinormal mode of the scalar field in the BTZ black hole background. We give a heuristic argument for the quasinormal decay, which is expected to apply to more general Vaidya spacetimes also in higher dimensions. This suggests a unified picture in which thermalization times of one- and two-point functions are determined by the lowest quasinormal mode. Finally, we study how these results compare to previous calculations of two-point functions based on the geodesic approximation.

We analyze the mechanism of condensation of orientational moduli [as introduced in Phys. Rev. D 87, 025025 (2013)] on multi-Skyrmionic configurations of the four-dimensional Skyrme model. The present analysis reveals interesting novel features. First of all, the orientational moduli tend to decrease the repulsive interactions between Skyrmions, the effect decreasing with the increase of the baryon number. Moreover, in the case of a single Skyrmion, the appearance of moduli is energetically favorable if finite-volume effects are present. Otherwise, in the usual flat topologically trivial case, it is not. In the low-energy theory these solutions can be interpreted as Skyrmions with additional isospin degrees of freedom.

Spontaneous chiral symmetry breaking in three-dimensional ($d=3$) quantum electrodynamics is understood as annihilation of an infrared-stable fixed point that describes the large-N conformal phase by another unstable fixed point at a critical number of fermions $N=N_c$. We discuss the root of universality of $N_c$ in this picture, together with some features of the phase boundary in the $(d,N)$ plane. In particular, it is shown that as $d\to 4$, $N_c\to 0$ with a constant slope, our best estimate of which suggests that $N_c=2.89$ in $d=3$.