We study the photon-to-meson transition form factors (TFFs) $F_{M\gamma }(Q^2)$ for $\gamma {\gamma }^{*}\to M$ using light-front holographic methods. The Chern-Simons action, which is a natural form in five-dimensional anti–de Sitter (AdS) space, is required to describe the anomalous coupling of mesons to photons using holographic methods and leads directly to an expression for the photon-to-pion TFF for a class of confining models. Remarkably, the predicted pion TFF is identical to the leading order QCD result where the distribution amplitude has asymptotic form. The Chern-Simons form is local in AdS space and is thus somewhat limited in its predictability. It only retains the $q\overline{q}$ component of the pion wave function, and further, it projects out only the asymptotic form of the meson distribution amplitude. It is found that in order to describe simultaneously the decay process ${\pi }^0\to \gamma \gamma$ and the pion TFF at the asymptotic limit, a probability for the $q\overline{q}$ component of the pion wave function $P_{q\overline{q}}=0.5$ is required, thus giving indication that the contributions from higher Fock states in the pion light-front wave function need to be included in the analysis. The probability for the Fock state containing four quarks $P_{q\overline{q}q\overline{q}}\sim 10\%$, which follows from analyzing the hadron matrix elements for a dressed current model, agrees with the analysis of the pion elastic form factor using light-front holography including higher Fock components in the pion wave function. The results for the TFFs for the $\eta$ and ${\eta }^{\prime }$ mesons are also presented. The rapid growth of the pion TFF exhibited by the BABAR data at high $Q^2$ is not compatible with the models discussed in this article, whereas the theoretical calculations are in agreement with the experimental data for the $\eta$ and ${\eta }^{\prime }$ TFFs.

We study the potential of the LHC to discover the signal of dark matter associated production with a photon induced by a dimension six effective operator, including next-to-leading order QCD corrections. We investigate the main backgrounds from the standard model, i.e. $Z$ boson and a photon associated production with invisible decay of $Z$ boson, and $Z$ boson and a jet production with the jet misidentified as a photon. We find that the $p_T^{\gamma }$ distributions of the backgrounds decrease faster than that of the signal with increasing of the transverse momentum of the photon. The ${\eta }^{\gamma }$ distributions of the backgrounds are almost flat in the full range of ${\eta }^{\gamma }$. In contrast, the signal lies mainly in the central region of ${\eta }^{\gamma }$. These characteristics may help to select the events in experiments. We show that in the parameter space allowed by the relic abundance constraint, which we have calculated at the next-to-leading-order QCD level, the LHC with $\sqrt{S}=7\mathrm{TeV}$ may discover this signal at the $5\sigma$ level after collecting an integrated luminosity of $1{\mathrm{fb}}^{-1}$. On the other hand, if this signal is not observed at the LHC, we can set a lower limit on the new physics scale at the $3\sigma$ level.

Nonleptonic decays of charmed mesons into two pseudoscalar mesons or one pseudoscalar meson and one vector meson are studied on the basis of a generalized factorization method considering the resonance effects in the pole model for the annihilation contributions. Large strong phases between different topological diagrams are considered in this work, simply taking the phase in the coefficients $a_i$. We find that the annihilation-type contributions calculated in the pole model are large in both of the $PP$ and $PV$ modes, which make our numerical results agree with the experimental data better than those previous calculations.

We consider new-physics (NP) contributions to the decay $t\to b\overline{b}c$. We parametrize the NP couplings by an effective Lagrangian consisting of 10 Lorentz structures. We show that the presence of NP can be detected through the measurement of the partial width. A partial identification of the NP can be achieved through the measurements of a forward-backward-like asymmetry, a top-quark-spin-dependent asymmetry, the partial-rate asymmetry, and a triple-product asymmetry. These observables, which vanish in the standard model, can all take values in the 10%–20% range in the presence of NP. Since $|V_{tb}{V}_{cb}|\simeq |V_{ts}{V}_{cs}|$, most of our results also hold, with small changes, for $t\to s\overline{s}c$.

We study single jet and prompt-photon inclusive hadroproduction with multi-Regge kinematics invoking the hypothesis of parton Reggeization in $t$-channel exchanges at high energy. In this approach, the leading contributions are due to the fusion of two Reggeized gluons into a Yang-Mills gluon and the annihilation of a Reggeized quark-antiquark pair into a photon, respectively. Adopting the Kimber-Martin-Ryskin and Blümlein prescriptions to derive unintegrated gluon and quark distribution functions of the proton from their collinear counterparts, for which we use the Martin-Roberts-Stirling-Thorne set, we evaluate cross section distributions in transverse momentum ($p_T$) and rapidity. Without adjusting any free parameters, we find good agreement with measurements by the CDF and D0 Collaborations at the Tevatron and by the ATLAS Collaboration at the LHC in the region $2p_T/\sqrt{S}\lesssim 0.1$, where $\sqrt{S}$ is the hadronic c.m. energy.

The most general phenomenological model involving a lepton triplet with hypercharge $\pm 1$ is constructed. A distinctive feature of this model is the prediction of a doubly charged lepton and a new heavy Dirac neutrino. We study the phenomenology of these exotic leptons both in low-energy experiments and at the LHC. The model predicts flavor-changing neutral-current processes such as muon and tau rare decays, which are studied in detail in order to constrain the model parameters. All the decay channels of the exotic leptons are described for a wide range of parameters. It is found that, if the mixing parameters between the exotic and light leptons are not too small ($>{10}^{-6}$), then they can be observable to a $3–5\sigma$ statistical significance at the 7 TeV LHC with $10–50{\mathrm{fb}}^{-1}$ luminosity for a 400 GeV mass and 14 TeV with $100–300{\mathrm{fb}}^{-1}$ luminosity for a 800 GeV mass.

Quasielastic neutrino-nucleon scattering is a basic signal process for neutrino oscillation studies. At accelerator energies, the corresponding cross section is subject to significant uncertainty due to the poorly constrained axial-vector form factor of the nucleon. A model-independent description of the axial-vector form factor is presented. Data from the MiniBooNE experiment for quasielastic neutrino scattering on ${}^{12}\mathrm{C}$ are analyzed under the assumption of a definite nuclear model. The value of the axial mass parameter, $m_A={0.85}_{-0.07}^{+0.22}\pm 0.09\mathrm{GeV}$, is found to differ significantly from extractions based on traditional form factor models. Implications for future neutrino scattering and pion electroproduction measurements are discussed.

We compute the triple gluon, quark-gluon and ghost-gluon vertices of QCD at the symmetric subtraction point at two loops in the $\overline{\mathrm{MS}}$ scheme. In addition we renormalize each of the three vertices in their respective momentum subtraction schemes, MOMggg, MOMq and MOMh. The conversion functions of all the wave functions, coupling constant and gauge parameter renormalization constants of each of the schemes relative to $\overline{\mathrm{MS}}$ are determined analytically. These are then used to derive the three loop anomalous dimensions of the gluon, quark, Faddeev-Popov ghost and gauge parameter as well as the $\beta$ function in an arbitrary linear covariant gauge for each MOM scheme. There is good agreement of the latter with earlier Landau gauge numerical estimates of Chetyrkin and Seidensticker.

Locality of interactions is an essential ingredient of Special Relativity. Recently, a new framework under the name of relative locality [G. Amelino-Camelia, L. Freidel, J. Kowalski-Glikman, and L. Smolin, arXiv:1101.0931.] has been proposed as a way to consider Planckian modifications of the relativistic dynamics of particles. We note in this paper that the loss of absolute locality is a general feature of theories beyond Special Relativity with an implementation of a relativity principle. We give an explicit construction of such an implementation and compare it both with the previously mentioned framework of relative locality and the so-called Doubly Special Relativity theories.

Numerical simulations of binary black holes—an important predictive tool for the detection of gravitational waves—are computationally expensive, especially for binaries with high mass ratios or with rapidly spinning constituent holes. Existing codes for evolving binary black holes rely on explicit time-stepping methods, for which the time-step size is limited by the smallest spatial scale through the Courant-Friedrichs-Lewy condition. Binary inspiral typically involves spatial scales (the spatial resolution required by a small or rapidly spinning hole) which are orders of magnitude smaller than the relevant (orbital, precession, and radiation-reaction) time scales characterizing the inspiral. Therefore, in explicit evolutions of binary black holes, the time-step size is typically orders of magnitude smaller than the relevant physical time scales. Implicit time-stepping methods allow for larger time steps, and they often reduce the total computational cost (without significant loss of accuracy) for problems dominated by spatial rather than temporal error, such as for binary-black-hole inspiral in corotating coordinates. However, fully implicit methods can be difficult to implement for nonlinear evolution systems like the Einstein equations. Therefore, in this paper we explore implicit-explicit (IMEX) methods and use them for the first time to evolve black-hole spacetimes. Specifically, as a first step toward IMEX evolution of a full binary-black-hole spacetime, we develop an IMEX algorithm for the generalized harmonic formulation of the Einstein equations and use this algorithm to evolve stationary and perturbed single-black-hole spacetimes. Numerical experiments explore the stability and computational efficiency of our method.

In this work, we study a modified theory of gravity that contains up to fourth order spatial derivatives as a model for the Hořava-Lifshitz gravity. The propagator is evaluated and, as a result, one extra pole is obtained, corresponding to a spin-2 nonrelativistic massless particle, an extra term which jeopardizes renormalizability, besides the unexpected general relativity unmodified propagator. Then unitarity is proved at the tree level, where the general relativity pole has been shown to have no dynamics, remaining only the 2 degrees of freedom of the new pole. Next, the nonrelativistic effective potential is determined from a scattering process of two identical massive gravitationally interacting bosons. In this limit, Newton’s potential is obtained, together with a Darwin-like term that comes from the extra nonpole term in the propagator. Regarding renormalizability, this extra term may be harmful by power counting, but it can be eliminated by adjusting the free parameters of the model. This adjustment is in accord with the detailed balance condition suggested in the literature and shows that the way in which extra spatial derivative terms are added is of fundamental importance.

We study the time evolution of the radial perturbation for self-gravitating soliton and black-hole solutions in a generalized Skyrme model in which a dilaton is present. The background solutions were obtained recently by some of the authors. For both the solitons and the black holes two branches of solutions exist which merge at some critical value of the corresponding parameter. The results show that, similar to the case without a scalar field, one of the branches is stable against radial perturbations and the other is unstable. The conclusions for the linear stability of the black holes in the generalized Skyrme model are also in agreement with the results from the thermodynamical stability analysis based on the turning point method.

Parity violation in interactions between the spacetime metric and other fields would be a sure sign of new physics. We examine the possibility of parity violation in the cosmological redshift. If right- and left-circularly polarized photons experience the redshift differently, the radiation from distant sources would tend to be depolarized, since the polarization states would accumulate different phases during propagation. The resulting birefringence has an unusual signature—depending on $z^2$—quite unlike what is seen in other theories, including those with violation of local boost invariance. The observed broad-spectrum polarization of $\gamma$-ray bursts constrains the fractional difference between the right- and left-handed redshifts at the $6\times {10}^{-37}$ level.

We discuss gravitational lensing in the Kehagias-Sfetsos space-time emerging in the framework of Hořava-Lifshitz gravity. In weak lensing, we show that there are three regimes, depending on the value of $\overline{\lambda }=1/\omega d^2$, where $\omega$ is the Hořava-Lifshitz parameter and $d$ characterizes the lensing geometry. When $\overline{\lambda }$ is close to zero, light deflection typically produces two images, as in Schwarzschild lensing. For very large $\overline{\lambda }$, the space-time approaches flatness, therefore there is only one undeflected image. In the intermediate range of $\overline{\lambda }$, only the upper focused image is produced due to the existence of a maximal deflection angle ${\delta }_{\max }$, a feature inexistent in the Schwarzschild weak lensing. We also discuss the location of Einstein rings, and determine the range of the Hořava-Lifshitz parameter compatible with present-day lensing observations. Finally, we analyze in the strong lensing regime the first two relativistic Einstein rings and determine the constraints on the parameter range to be imposed by forthcoming experiments.

We present an experimental opportunity for the future to measure possible violations to Newton’s $1/r^2$ law in the 0.1–10 m range using dynamic gravity field generators (DFG) and taking advantage of the exceptional sensitivity of modern interferometric techniques. The placement of a DFG in proximity to one of the interferometer’s suspended test masses generates a change in the local gravitational field that can be measured at a high signal to noise ratio. The use of multiple DFGs in a null-experiment configuration allows us to test composition-independent non-Newtonian gravity significantly beyond the present limits. Advanced and third-generation gravitational-wave detectors are representing the state-of-the-art in interferometric distance measurement today, therefore, we illustrate the method through their sensitivity to emphasize the possible scientific reach. Nevertheless, it is expected that due to the technical details of gravitational-wave detectors, DFGs shall likely require dedicated custom-configured interferometry. However, the sensitivity measure we derive is a solid baseline indicating that it is feasible to consider probing orders of magnitude into the pristine parameter well beyond the present experimental limits significantly cutting into the theoretical parameter space.

The incorporation of a small cosmological constant within radiatively broken scale-invariant models is discussed. We show that phenomenologically consistent scale-invariant models can be constructed which allow a small positive cosmological constant, providing certain relation between the particle masses is satisfied. As a result, the mass of the dilaton is generated at two-loop level. Another interesting consequence is that the electroweak symmetry-breaking vacuum in such models is necessarily a metastable “false” vacuum which, fortunately, is not expected to decay on cosmological time scales.

Inspired by the newly observed two charged bottomoniumlike states, we consider the possible contribution from the intermediate $Z_b(10610)$ and $Z_b(10650)$ states to the ${\rm Y}(5S)\to {\rm Y}(2S){\pi }^{+}{\pi }^{-}$ decay process, which naturally explains Belle’s previous observation of the anomalous ${\rm Y}(2S){\pi }^{+}{\pi }^{-}$ production near the peak of ${\rm Y}(5S)$ at $\sqrt{s}=10.87\mathrm{GeV}$ [K. F. Chen et al. (Belle Collaboration), Phys. Rev. Lett. 100, 112001 (2008)]. The resulting $d\Gamma ({\rm Y}(5S)\to {\rm Y}(2S){\pi }^{+}{\pi }^{-})/d{m}_{{\pi }^{+}{\pi }^{-}}$ and $d\Gamma ({\rm Y}(5S)\to {\rm Y}(2S){\pi }^{+}{\pi }^{-})/d\cos \theta$ distributions agree with Belle’s measurement after inclusion of these $Z_b$ states. This formalism also reproduces the Belle observation of the double-peak structure and its reflection in the ${\rm Y}(2S){\pi }^{+}$ invariant mass spectrum of the ${\rm Y}(5S)\to {\rm Y}(2S){\pi }^{+}{\pi }^{-}$ decay.

The transversity generalized parton distributions (tGPDs) of the pion, involving matrix elements of the tensor bilocal quark current, are analyzed in chiral quark models. We apply the nonlocal chiral models involving a momentum-dependent quark mass, as well as the local Nambu–Jona-Lasinio with the Pauli-Villars regularization to calculate the pion tGPDs, as well as related quantities following from restrained kinematics, evaluation of moments, or taking the Fourier-Bessel transforms to the impact-parameter space. The obtained distributions satisfy the formal requirements, such as proper support and polynomiality, following from Lorentz covariance. We carry out the leading-order QCD evolution from the low quark-model scale to higher lattice scales, applying the method of Kivel and Mankiewicz. We evaluate several lowest-order generalized transversity form factors, accessible from the recent lattice QCD calculations. These form factors, after evolution, agree properly with the lattice data, in support of the fact that the spontaneously broken chiral symmetry is the key element also in the evaluation of the transversity observables.

We study the spectral functions of fermionic operators in $1+1$-dimensional $SU(N)$ super Yang-Mills theory with 16 supercharges at finite density using the holographically dual D1 brane geometry. This system exhibits quasiparticle peaks indicating the existence of Fermi points about which excitations have a finite relaxation time, in contrast with the Tomonaga-Luttinger model. The finite width may be attributed to the nontrivial interactions of the probe operators with the background density matrix, modeled holographically as a charged black hole. We show that the fermionic correlators can in fact be deduced from known results for fermion probes of the charged ${\mathrm{AdS}}_4$ black hole background, owing to some remarkable coincidences in supergravity truncations.