$CP$ violation in the loop-mediated photon-photon interactions would modify the birefringence of the quantum vacuum. We discuss the implications of this effect on an experiment in which light propagates in a Fabry-Perot cavity permeated by a time-dependent electric and magnetic field: for some suitable orientation of the electric field, the effect does not cancel out in a round-trip. We show that the violation of $CP$ would imply the existence of characteristic Fourier components, in the intensity spectrum of the outgoing wave. In order to estimate the magnitude of this effect within the standard model, we use chiral perturbation theory to compute the $\theta$-term contribution to the coefficient of the leading $CP$-odd vertex, in the low-energy effective field theory for photon dynamics.

We consider the influence of extra dimensions on the force in Casimir pistons. Suitable analytical expressions are provided for the Casimir force in the range where the plate distance is small, and where it is large, compared to the size of the extra dimensions. We show that the Casimir force tends to move the center plate toward the closer wall; this result is true independently of the cross section of the piston and the geometry or topology of the additional Kaluza-Klein dimensions. The statement also remains true at finite temperature. In the limit where one wall of the piston is moved to infinity, the result for parallel plates is recovered. If only one chamber is considered, a criterion for the occurrence of Lukosz-type repulsion, as opposed to the occurrence of renormalization ambiguities, is given; we comment on why no repulsion has been noted in some previous cosmological calculations that consider only two plates.

We investigate a class of theories involving a symmetric two-tensor field in Minkowski spacetime with a potential triggering spontaneous violation of Lorentz symmetry. The resulting massless Nambu-Goldstone modes are shown to obey the linearized Einstein equations in a fixed gauge. Imposing self-consistent coupling to the energy-momentum tensor constrains the potential for the Lorentz violation. The nonlinear theory generated from the self-consistent bootstrap is an alternative theory of gravity, containing kinetic and potential terms along with a matter coupling. At energies small compared to the Planck scale, the theory contains general relativity, with the Riemann-spacetime metric constructed as a combination of the two-tensor field and the Minkowski metric. At high energies, the structure of the theory is qualitatively different from general relativity. Observable effects can arise in suitable gravitational experiments.

In this work, we show that the traditional effective field approach can be applied to the $\mathcal{P}\mathcal{T}$-symmetric wrong sign ($-x^4$) quartic potential. The importance of this work lies in the possibility of its extension to the more important $\mathcal{P}\mathcal{T}$-symmetric quantum field theory while the other approaches which use complex contours are not willing to be applicable. We calculated the effective potential of the massless $-x^4$ theory as well as the full spectrum of the theory. Although the calculations are carried out up to first order in the coupling, the predicted spectrum is very close to the exact one taken from other works. The most important result of this work is that the effective potential obtained, which is equivalent to the Gaussian effective potential, is bounded from below while the classical potential is bounded from above. This explains the stability of the vacuum of the theory. The obtained quasiparticle Hamiltonian is non-Hermitian but $\mathcal{P}\mathcal{T}$ symmetric and we showed that the calculation of the metric operator can go perturbatively. In fact, the calculation of the metric operator can be done even for higher dimensions (quantum field theory) which, up until now, cannot be calculated in the other approaches either perturbatively or in a closed form due to the possible appearance of field radicals. Moreover, we argued that the effective theory is perturbative for the whole range of the coupling constant and the perturbation series is expected to converge rapidly (the effective coupling $g_{\mathrm{eff}}=\frac{1}{6}$).

Recently we suggested a solution-generating technique for five-dimensional supergravity with three Abelian vector fields based on the hidden $SO(4,4)$ symmetry of the three-dimensionally reduced theory. This technique generalizes the $G_{2(2)}$ generating technique developed earlier for minimal five-dimensional supergravity (A. Bouchareb, G. Clément, C-M. Chen, D. V. Gal’tsov, N. G. Scherbluk, and Th. Wolf, Phys. Rev. D 76, 104032 (2007)) and provides a new matrix representation for cosets forming the corresponding sigma-models in both cases. Here we further improve these methods introducing a matrix-valued dualization procedure which helps to avoid difficulties associated with solving the dualization equations in the component form. This new approach is used to generate a five-parametric rotating charged Kaluza-Klein black hole with the squashed horizon adding one parameter more to the recent solution by Tomizawa, Yasui, and Morisawa, which was constructed using the previous version of the $G_{2(2)}$ generating technique.

All the boundary conditions compatible with the reduction of a five-dimensional spinor field of bulk mass $M$ in a compactified warped space to a four-dimensional brane are derived from the Hermiticity conditions of the relevant operator. The possible presence of metric singularities is taken into account. Examples of resulting Kaluza-Klein spinor towers are given for a representative set of values for the basic parameters of the model and of the parameters describing the allowed boundary conditions, within the hypothesis that there exists one-mass-scale-only, the Planck mass. In many cases, the lowest mass in the tower is small and very sensitive to the parameters while the other masses are much higher and become more regularly spaced. In these cases, if a basic fermion of the standard model (lepton or quark) happens to be the lowest mass of a Kaluza-Klein tower, the other masses would be much larger and weakly dependent on the fermion which defines the tower.

The gravitational growth index formalism provides a model independent way to look for deviations from general relativity by testing dark energy physics distinct from its effects on the cosmic expansion history. Here we extend the approach to incorporate an early time parameter $g_{\star }$ in addition to the growth index in describing the growth of large-scale structure. We illustrate its utility for models with modified gravity at high redshift, early acceleration, or early dark energy. Future data will have the capability to constrain the dark energy equation of state, the growth index $\gamma$, and $g_{\star }$ simultaneously, with no degradation in the equation of state determination.

We show that a semiclassical polymerization of the interior of Schwarzschild black holes gives rise to a tantalizing candidate for a nonsingular, single-horizon black hole spacetime. The exterior has nonzero quantum stress energy but closely approximates the classical spacetime for macroscopic black holes. The interior exhibits a bounce at a microscopic scale and then expands indefinitely to a Kantowski-Sachs spacetime. Polymerization therefore removes the singularity and produces a scenario reminiscent of past proposals for universe creation via quantum effects inside a black hole.

We study flavor violation in the quark sector in a purely $4D$, two-site effective field theory description of the standard model (SM) and just their first Kaluza-Klein excitations from a warped extra dimension. The warped $5D$ framework can provide solutions to both the Planck-weak and flavor hierarchies of the SM. It is also related (via the AdS/CFT correspondence) to partial compositeness of the SM. We focus on the dominant contributions in the two-site model to two observables which we argue provide the strongest constraints from flavor violation, namely, ${ϵ}_K$ and $\mathrm{BR}(b\to s\gamma )$, where contributions in the two-site model occur at tree and loop-level, respectively. In particular, we demonstrate that a “tension” exists between these two observables in the sense that they have opposite dependence on composite site Yukawa couplings, making it difficult to decouple flavor-violating effects using this parameter. We choose the size of the composite site QCD coupling based on the relation of the two-site model to the $5D$ model (addressing the Planck-weak hierarchy), where we match the $5D$ QCD coupling to the $4D$ coupling at the loop-level and assuming negligible tree-level brane-localized kinetic terms. We estimate that a larger size of the $5D$ gauge coupling is constrained by the requirement of $5D$ perturbativity. We find that $\sim O(5)\mathrm{TeV}$ mass scale for the new particles in the two-site model can then be consistent with both observables. We also compare our analysis of ${ϵ}_K$ in the two-site model to that in $5D$ models, including both the cases of a brane-localized and bulk Higgs.

We perform a numerical analysis of Higgs-to-Higgs decays within a type II two-Higgs-doublet model (2HDM), highlighting several channels that cannot occur in its supersymmetric version, thereby allowing one to possibly distinguish between these two scenarios. Our results are compliant with all available experimental bounds from both direct and indirect Higgs searches and with theoretical constraints from vacuum stability and perturbative unitarity.

We study in an effective operator approach how the effects of new physics from various scenarios that contain an extra $Z^{\prime }$ neutral gauge boson or doubly charged scalars, can affect and thus be tested by the precision polarized Møller scattering experiments. We give Wilson coefficients for various classes of generic models, and we deduce constraints on the parameter space of the relevant coupling constants or mixing angles from the results of the SLAC E158 experiment where applicable. We give also constraints projected from the upcoming 1 ppb JLAB experiment. In the scenario where the extra $Z^{\prime }$ is light ($M_{Z^{\prime }}\ll M_W$), we obtain further constraints on the parameter space using the BNL $g-2$ result where it is useful. We find that the BNL deviation from the standard model cannot be attributed to a light extra $Z^{\prime }$ neutral gauge boson.

In a relativistic setting, hydrodynamic calculations which include shear viscosity (which is first order in an expansion in gradients of the flow velocity) are unstable and acausal unless they also include terms to second order in gradients. To date such terms have only been computed in supersymmetric $\mathcal{N}=4$ super–Yang-Mills theory at infinite coupling. Here we compute these second-order hydrodynamic coefficients in weakly coupled QCD, perturbatively to leading order in the QCD coupling, using kinetic theory. We also compute them in QED and scalar $\lambda {\varphi }^4$ theory.

Charm production gives rise to a flux of very high energy neutrinos from astrophysical sources with jets driven by central engines, such as gamma ray bursts or supernovae with jets. The neutrino flux from semileptonic decays of charmed mesons is subject to much less hadronic and radiative cooling than the conventional flux from pion and kaon decays and therefore has a dominant contribution at higher energies, which is of relevance to future ultrahigh energy neutrino experiments.

We present measurements of the branching fraction and fraction of longitudinal polarization for the decay $B^{+}\to {\overline{K}}^{*0}{K}^{*+}$ with a sample of $(467\pm 5)\times {10}^6$ $B\overline{B}$ pairs collected with the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider at the SLAC National Accelerator Laboratory. We obtain the branching fraction $\mathcal{B}(B^{+}\to {\overline{K}}^{*0}{K}^{*+})=(1.2\pm 0.5\pm 0.1)\times {10}^{-6}$ with a significance of 3.7 standard deviations including systematic uncertainties. We measure the fraction of longitudinal polarization $f_L={0.75}_{-0.26}^{+0.16}\pm 0.03$. The first error quoted is statistical and the second is systematic.

Many string constructions have a classical no-scale structure, resulting in a one-parameter model (OPM) for the supersymmetry breaking soft terms. As a highly constrained subset of mSUGRA, the OPM has the potential to be predictive. Conversely, if the observed superpartner spectrum at LHC is a subset of the OPM parameter space, then this may provide a clue to the underlying theory at high energies. We investigate the allowed supersymmetry parameter space for a generic one-parameter model taking into account the most recent experimental constraints. We find that, in the strict moduli scenario, there are no regions of the parameter space which may satisfy all constraints. However, for the dilaton scenario, there are small regions of the parameter space where all constraints may be satisfied and for which the observed dark matter density may be generated. We also survey the possible signatures which may be observable at the Large Hadron Collider (LHC). Finally, we compare collider signatures of OPM to those from a model with nonuniversal soft terms, in particular, those of an intersecting $D6$-brane model. We find that it may be possible to distinguish between these diverse scenarios at LHC.

We study baryons in $SU(N)$ gauge theories at finite temperature according to the gauge/string correspondence based on IIB string theory. The baryon is constructed out of the D5-brane and $N$ fundamental strings to form a color singlet $N$-quark bound state. At finite temperature and in the deconfining phase, we could find $k(<N)$-quark baryons. Thermal properties of such $k$-quark baryons and also of the $N$-quark baryon are examined. We study the temperature dependence of color screening distance and the Debye length of the baryon of the $k$ quark and the $N$ quark. We also estimate the melting temperature, where the baryons decay into quarks and gluons completely.

We study probe D5 branes in D3 brane ${\mathrm{AdS}}_5$ and ${\mathrm{AdS}}_5$-Schwarzschild backgrounds as a prototype dual description of strongly coupled $2+1$ dimensional quasiparticles. We introduce a chemical potential through the $\mathrm{U}(1{)}_R$ symmetry group, U(1) baryon number, and a U(1) of isospin in the multiflavor case. We find the appropriate D5 embeddings in each case—the embeddings do not exhibit the spontaneous symmetry breaking that would be needed for a superconductor. The isospin chemical potential does induce the condensation of charged meson states.

We discuss the phenomenology of a toy intersecting brane model where supersymmetry is dynamically broken in an open-string hidden sector and gauge-mediated to the visible sector. Scalar masses $\sim \mathrm{TeV}$ are easily realizable, and $R$-symmetry is broken. These ideas are easily generalizable to other intersecting brane models.

We measure the gravitational recoil for unequal-mass black-hole binary mergers, with the larger black hole having intrinsic spin $a/m^H=0.8$, and the smaller black hole nonspinning. We choose our configurations such that, initially, the spins lie on the orbital plane. The spin and orbital plane precess significantly (we introduce a technique to identify the orbital plane at merger), and we find that the out-of plane recoil (i.e. the recoil perpendicular to the orbital plane around merger) varies as ${\eta }^2/(1+q)$, in agreement with our previous prediction, based on the post-Newtonian scaling.