We provide a nonperturbative expression for the hadron production in electron-positron annihilation at zero temperature in a strongly coupled, large-$N_{\mathrm{c}}$ $SU(N_{\mathrm{c}})$ field theory with $N_{\mathrm{f}}\ll N_{\mathrm{c}}$ quark flavors. The resulting expressions are valid to leading order in the electromagnetic coupling constant but nonperturbatively in the $SU(N_{\mathrm{c}})$ interactions and the mass of the quark. We obtain this quantity by computing the imaginary part of the hadronic vacuum polarization function ${\Pi }_q$ using holographic techniques, providing an alternative to the known method that uses the spectrum of infinitely stable mesons determined by the normalizable modes of the appropriated fields in the bulk. Our result exhibits a structure of poles localized at specific real values of $q^2$, which coincide with the ones found using the normalizable modes, and extends it offering the unique analytic continuation of this distribution to a function defined for values of $q^2$ over the complex plane. This analytic continuation permits to include a finite decay width for the mesons. By comparison with experimental data we find qualitatively good agreement on the shape of the first pole, when using the $\rho$ meson parameters and choosing a proper normalization factor. We then estimate the contribution to the anomalous magnetic moment of the muon finding an agreement within 25%, for this choice of parameters.

A particular framework for quantum gravity is the doubly special relativity (DSR) formalism that introduces a new observer independent scale, the Planck energy. Our aim in this paper is to study the effects of this energy upper bound in relativistic thermodynamics. We have explicitly computed the modified equation of state for an ideal fluid in the DSR framework. In deriving our result we exploited the scheme of treating DSR as a nonlinear representation of the Lorentz group in special relativity.

In this paper we construct closed expressions that correspond to the topological charges of the various $1/2$-BPS states of the maximal 10- and 11-dimensional supergravity theories. These expressions are related to the structure of the supersymmetry algebras in curved spacetimes. We mainly focus on IIB supergravity and 11-dimensional supergravity in a double M9-brane background, with an emphasis on the $SL(2,\mathbb{R})$ multiplet structure of the charges and how these map between theories. This includes the charges corresponding to the multiplets of 7- and 9-branes in IIB. We find that examining the possible multiplet structures of the charges provides another tool for exploring the spectrum of BPS states that appear in these theories. As a prerequisite to constructing the charges we determine the field equations and multiplet structure of the 11-dimensional gauge potentials, extending previous results on the subject. The massive gauge transformations of the fields are also discussed. We also demonstrate how these massive gauge transformations are compatible with the construction of an $SL(2,\mathbb{R})$ covariant kinetic term in the 11-dimensional Kaluza-Klein monopole worldvolume action.

We discuss the possibility to perform and use the exact Foldy-Wouthuysen transformation (EFWT) for the Dirac spinor coupled to different $CPT$ and Lorentz violating terms. The classification of such terms is performed, selecting those of them which admit EFWT. For the particular example of an axial vector field, which can be associated with the completely antisymmetric torsion, we construct an explicit EFWT in the case when only a timelike component of this axial vector is present. In the cases when EFWT is not possible, one can still use the corresponding technique for deriving the perturbative Foldy-Wouthuysen transformation, as is illustrated in a particular example in the Appendix.

We use the connection between the $U$-duality groups in $d=5$ and $d=4$ to derive properties of the $\mathcal{N}=8$ black hole potential and its critical points (attractors). This approach allows us to study and compare the supersymmetry features of different solutions.

We continue the recent study of the possibility of constructing a consistent infrared modification of gravity by treating the vierbein and connection as independent dynamical fields. We present the generalized Fierz-Pauli equation that governs the propagation of a massive spin-2 mode in a model of this sort in the backgrounds of arbitrary torsionless Einstein manifolds. We show explicitly that the number of propagating degrees of freedom in these backgrounds remains the same as in flat space-time. This generalizes the recent result that the Boulware-Deser phenomenon does not occur in de Sitter and anti-de Sitter backgrounds. We find that, at least for weakly curved backgrounds, there are no ghosts in the model. We also discuss the interaction of sources in flat background. It is generally believed that the spinning matter is the only source of torsion. Our flat space study shows that this is not the case. We demonstrate that an ordinary conserved symmetric energy-momentum tensor can also generate torsion fields and thus excite massive spin-2 degrees of freedom.

We introduce in $f(R)$ gravity-Palatini formalism the method of the inverse problem to extract the action from the expansion history of the Universe. First, we use an ansatz for the scale factor and apply the inverse method to derive an appropriate action for the gravity. In the second step we use the supernova type Ia data set from the Union sample and obtain a smoothed function for the Hubble parameter up to the redshift 1.7. We apply the smoothed Hubble parameter in the inverse approach and reconstruct the corresponding action in $f(R)$ gravity. In the next step we investigate the viability of reconstruction method, doing a Monte Carlo simulation we generate synthetic SNIa data with the quality of the Union sample and show that roughly more than 1500 SNIa data is essential to reconstruct correct action. Finally, with enough SNIa data, we propose two diagnosis in order to distinguish between the $\Lambda \mathrm{CDM}$ model and an alternative theory for the acceleration of the Universe.

We study spherically symmetric structures in conformal gravity and in a scalar-tensor extension and gain some more insight about these gravitational theories. In both cases we analyze solutions in two systems: perfect fluid solutions and boson stars of a self-interacting complex scalar field. In the purely tensorial (original) theory we find in a certain domain of parameter space finite mass solutions with a linear gravitational potential but without a Newtonian contribution. The scalar-tensor theory exhibits a very rich structure of solutions whose main properties are discussed. Among them, solutions with a finite radial extension, open solutions with a linear potential and logarithmic modifications and also a (scalar-tensor) gravitational soliton. This may also be viewed as a static self-gravitating boson star in purely tensorial conformal gravity.

Gravitational waves from compact objects provide information about their structure, probing deep into strong-gravity regions. Here we illustrate how the presence or absence of an event horizon can produce qualitative differences in the gravitational waves emitted by ultracompact objects. In order to set up a straw-man ultracompact object with no event horizon, but which is otherwise almost identical to a black hole, we consider a nonrotating thin-shell model inspired by Mazur and Mottola’s gravastar, which has a Schwarzschild exterior, a de Sitter interior and an infinitely thin shell with finite tension separating the two regions. As viewed from the external space-time, the shell can be located arbitrarily close to the Schwarzschild radius, so a gravastar might seem indistinguishable from a black hole when tests are only performed on its external metric. We study the linearized dynamics of the system, and, in particular, the junction conditions connecting internal and external gravitational perturbations. As a first application of the formalism we compute polar and axial oscillation modes of a thin-shell gravastar. We show that the quasinormal mode spectrum is completely different from that of a black hole, even in the limit when the surface redshift becomes infinite. Polar quasinormal modes depend on the equation of state of matter on the shell and can be used to distinguish between different gravastar models. Our calculations suggest that low-compactness gravastars could be unstable when the sound speed on the shell $v_s/c\gtrsim 0.92$.

Asymptotically anti–de Sitter rotating black holes for the Bergshoeff-Hohm-Townsend massive gravity theory in three dimensions are considered. In the special case when the theory admits a unique maximally symmetric solution, apart from the mass and the angular momentum, the black hole is described by an independent “gravitational hair” parameter, which provides a negative lower bound for the mass. This bound is saturated at the extremal case, and since the temperature and the semiclassical entropy vanish, it is naturally regarded as the ground state. The absence of a global charge associated with the gravitational hair parameter reflects itself through the first law of thermodynamics in the fact that the variation of this parameter can be consistently reabsorbed by a shift of the global charges, giving further support to consider the extremal case as the ground state. The rotating black hole fits within relaxed asymptotic conditions as compared with the ones of Brown and Henneaux, such that they are invariant under the standard asymptotic symmetries spanned by two copies of the Virasoro generators, and the algebra of the conserved charges acquires a central extension. Then it is shown that Strominger’s holographic computation for general relativity can also be extended to the Bergshoeff-Hohm-Townsend theory; i.e., assuming that the quantum theory could be consistently described by a dual conformal field theory at the boundary, the black hole entropy can be microscopically computed from the asymptotic growth of the number of states according to Cardy’s formula, in exact agreement with the semiclassical result.

The origin of large-scale magnetic field in the Universe is one of the greatest mysteries in modern cosmology. We present a new mechanism for generation of large-scale magnetic field, based on the power-counting renormalizable theory of gravitation recently proposed by Hořava. Contrary to the usual case in general relativity, the $U(1)$ gauge symmetry of a Maxwell action in this theory permits terms breaking conformal invariance in the ultraviolet. Moreover, for high frequency modes, the anisotropic scaling intrinsic to the theory inevitably makes the sound horizon far outside the Hubble horizon. Consequently, noninflationary cosmic expansion in the early Universe naturally generates superhorizon quantum fluctuations of the magnetic field. Specializing our consideration to the case with the dynamical critical exponent $z=3$, we show an explicit set of parameters for which (i) the amplitude of generated magnetic field is large enough as a seed for the dynamo mechanism; (ii) backreaction to the cosmic expansion is small enough; and (iii) the high-energy dispersion relation is consistent with the most recent observational limits from MAGIC and Fermi collaborations.

We study non-Gaussianities in the primordial perturbations in single field inflation where there is a radiation era prior to inflation. Inflation takes place when the energy density of radiation drops below the value of the potential of a coherent scalar field. We compute the thermal average of the two-point, three-point, and four-point correlation functions of inflaton fluctuations. The three-point function is proportional to the slow-roll parameters, and there is an amplification in $f_{\mathrm{NL}}$ by a factor of 65 to 90 due to the contribution of the thermal bath. We conclude that the bispectrum is in the range of detectability with the 21-cm anisotropy measurements. The four-point function on the other hand appears in this case due to the thermal averaging and the fact that thermal averaging of the four-point correlation is not the same as the square of the thermal averaging of the two-point function. Because of this fact, ${\tau }_{\mathrm{NL}}$ is not proportional to the slow-roll parameters and can be as large as $-42$. The non-Gaussianities in the four-point correlation of the order 10 can also be detected by 21-cm background observations. We conclude that a signature of thermal inflatons is a large trispectrum non-Gaussianity compared to the bispectrum non-Gaussianity.

A new relativistic formulation of MOND is advanced, involving two metrics as independent degrees of freedom: the MOND metric $g_{\mu \nu }$, to which alone matter couples, and an auxiliary metric ${\widehat{g}}_{\mu \nu }$. The main idea hinges on the fact that we can form tensors from the difference of the Levi-Civita connections of the two metrics, $C_{\beta \gamma }^{\alpha }={\Gamma }_{\beta \gamma }^{\alpha }-{\widehat{\Gamma }}_{\beta \gamma }^{\alpha }$, and these act like gravitational accelerations. In the context of MOND, we can form dimensionless “acceleration” scalars and functions thereof (containing only first derivatives) from contractions of $a_0^{-1}{C}_{\beta \gamma }^{\alpha }$. I look at a subclass of bimetric MOND theories governed by the action $I=-(16\pi G{)}^{-1}\int [\beta g^{1/2}R+\alpha {\widehat{g}}^{1/2}\widehat{R}-2(g\widehat{g}{)}^{1/4}f(\kappa )a_0^2\mathcal{M}(\widetilde{{\rm Y}}/a_0^2)]d^{4}x+I_M(g_{\mu \nu },{\psi }_i)+{\widehat{I}}_M({\widehat{g}}_{\mu \nu },{\chi }_i)$, with $\widetilde{{\rm Y}}$ as a scalar quadratic in the $C_{\beta \gamma }^{\alpha }$, $\kappa =(g/\widehat{g}{)}^{1/4}$, $I_M$ as the matter action, and allow for the existence of twin matter that couples to ${\widehat{g}}_{\mu \nu }$ alone. Thus, gravity is modified not by modifying the elasticity of the space-time in which matter lives, but by the interaction between that space-time and the auxiliary one. In particular, I concentrate on the interesting and simple choice $\widetilde{{\rm Y}}\propto g^{\mu \nu }(C_{\mu \lambda }^{\gamma }{C}_{\nu \gamma }^{\lambda }-C_{\mu \nu }^{\gamma }{C}_{\lambda \gamma }^{\lambda })$. This theory introduces only one new constant, $a_0$; it tends simply to general relativity (GR) in the limit $a_0\to 0$ and to a phenomenologically valid MOND theory in the nonrelativistic limit. The theory naturally gives MOND and “dark energy” effects from the same term in the action, both controlled by the MOND constant $a_0$. In regards to gravitational lensing by nonrelativistic systems–a holy grail for relativistic MOND theories–the theory predicts that the same potential that controls massive-particle motion also dictates lensing in the same way as in GR: Lensing and massive-particle probing of galactic fields will require the same “halo” of dark matter to explain the departure of the present theory from GR. This last result can be modified with other choices of $\widetilde{{\rm Y}}$, but lensing is still enhanced and MOND-like, with an effective logarithmic potential.

We compare two strategies of multidetector detection of compact binary inspiral signals, namely, the coincidence and the coherent for the realistic case of geographically separated detectors. The naive coincident strategy treats the detectors as if they are isolated—compares individual detector statistics with their respective thresholds while the coherent strategy combines the detector network data coherently to obtain a single detection statistic which is then compared with a single threshold. We also consider an enhanced coincidence strategy which is intermediate in the sense that though the individual statistics are added in quadrature and the sum compared with a single threshold, the estimated parameters are also checked for consistency. For simplicity, we consider detector pairs having the same power spectral density of noise, as that of initial LIGO and also assume the noise to be stationary and Gaussian. Further, since we consider the detectors to be widely separated on Earth, we take the instrumental noises to be uncorrelated; the wide separation implicitly means that since the detector arms must lie parallel to the Earth’s surface, the detectors necessarily have different orientations. We compare the performances of the methods by plotting the receiver operating characteristics for the strategies. Several results are derived analytically in order to gain insight. Simulations are performed in order to plot the receiver operating characteristic (ROC) curves. A single astrophysical source as well as a distribution of sources is considered. We assume a 1 yr data train and a mass range of $1–40M_{\odot }$ for the case of astrophysically distributed sources. We find that the coherent strategy is superior to the two coincident strategies that we consider. Remarkably, the detection probability of the coherent strategy is 50% better than the naive coincident strategy. One the other hand, the difference in performance between the coherent strategy and enhanced coincident strategy is not very large. Even in this situation, it is not difficult to perform the real data analysis with the coherent strategy. The bottom line is that the coherent strategy is a good detection strategy.

Active galactic nuclei (AGNs) have been one of the most widely discussed sources of ultrahigh-energy cosmic rays (UHECRs). The recent results of the Pierre Auger observatory have indicated a possible composition change of UHECRs above $\sim {10}^{18.5}\mathrm{eV}$ toward heavy nuclei. We show here that if indeed UHECRs are largely heavy nuclei, then nearby radio-quiet AGNs can also be viable sources of UHECRs. We derive constraints on the acceleration sites which enable acceleration of UHECRs to ${10}^{20}\mathrm{eV}$ without suffering losses. We show that the acceleration of UHECRs and the survival of energetic heavy nuclei are possible in the parsec-scale weak jets that are typically observed in these objects, the main energy loss channel being photodisintegration. On this scale, energy dissipation by shock waves resulting from interactions inside a jet or of the jet with surrounding material are expected, which may accelerate the particles up to very high energies. We discuss the possible contribution of radio-quiet AGNs to the observed UHECR flux, and show that the required energy production rate in UHECRs by a single object could be as low as $\approx 3\times {10}^{39}\mathrm{erg}{\mathrm{s}}^{-1}$, which is less than a percent of the bolometric luminosity, and thus energetically consistent. We discuss consequences of this model, the main one being the difficulty in detecting energetic secondaries ($\gamma$-rays and neutrinos) from the same sources.

We report the first precision measurement of the frequency-dependent property of the effective torsion spring constant for a tungsten fiber by using two disk pendulums with different moments of inertia. A quartz fiber with $Q\approx 3.36\times {10}^5$ was used to determine the ratio of the moments of inertia of two pendulums. The experimental result indicated that the torsion spring constant of the tungsten fiber was dependent on the oscillation frequency by $\Delta K/\Delta ({\omega }^2)=(0.954\pm 0.084)\times {10}^{-8}{\mathrm{kgm}}^2$ at $\sim \mathrm{mHz}$ range, which suggested that the resultant bias in our $G$ measurement with the time-of-swing method was $\Delta G/G=(211.80\pm 18.69)\mathrm{ppm}$ as reported recently by Jun Luo et al. [Phys. Rev. Lett. 102, 240801 (2009)]. This experiment provided the first direct test to the Kuroda-Newman effect that predicted an upward bias in a $G$ measurement with the time-of-swing method.

We propose a new radial coordinate to write the Kerr metric in puncture form. Unlike the quasiradial coordinate introduced previously, the horizon radius remains finite in our radial coordinate in the extreme Kerr limit $a/M\to 1$. This significantly improves the accuracy of the evolution of black holes with spins close to the extreme Kerr limit. We are able to evolve accurately both stationary and boosted black holes with spins as high as $a/M=0.99$ using initial data constructed in these new puncture coordinates. Initial data of compact binaries with rapidly spinning black holes can be constructed using our proposed new puncture metric for the background conformal metric. Our simulations for single black holes suggest that such initial data can be evolved successfully by the moving puncture technique.

We obtain modified dispersion relations by requiring the vanishing of determinant of inverse of modified photon propagators in Lorentz invariance violation (LIV) theory. Inspired by these dispersion relations, we give a more general dispersion relation with less assumptions and apply it to the recent observed gamma-ray burst GRB090510 to extract various constraints on LIV parameters. We find that the constraint on quantum gravity mass is slightly larger than the Planck mass but is consistent with other recent observations, so the corresponding LIV coefficient ${\xi }_1$ has reached the natural order [$\mathcal{O}(1)$] as one expects. From our analysis, the linear LIV corrections to photon group velocity might be not excluded yet.

We propose new mechanisms for ameliorating the constraints on the Kaluza-Klein mass scale from charged lepton flavor violation in the framework of the standard model fields propagating in a warped extra dimension, especially in models accounting for neutrino data. These mechanisms utilize the extended five-dimensional (5D) electroweak gauge symmetry $[SU(2{)}_L\times SU(2{)}_R\times U(1{)}_X]$ which is already strongly motivated in order to satisfy electroweak precision tests in this framework. We show that new choices of representations for leptons under this symmetry (naturally) can allow small mixing angles for left-handed (LH) charged leptons and simultaneously large mixing angles for their $SU(2{)}_L$ partners, i.e., the LH neutrinos, with the neutrino data being accounted for by the latter mixings. Enhancement of charged lepton flavor violation by the large mixing angle observed in leptonic charged currents, which is present for the minimal choice of representations where the LH charged lepton and neutrino mixing angles are similar, can thus be avoided in these models. This idea might also be useful for suppressing the contributions to $B_{d,s}$ mixing in this framework and in order to suppress flavor violation from exchange of superpartners (instead of from KK modes) in 5D “flavorful supersymmetry” models. Additionally, the less minimal representations can provide custodial protection for shifts in couplings of fermions to $Z$ and, in turn, further suppress charged lepton flavor violation from tree-level $Z$ exchange in the warped extra-dimensional scenario. As a result, $\sim O(3)\mathrm{TeV}$ KK mass scale can be simultaneously consistent with charged lepton flavor violation and neutrino data, even without any particular structure in the 5D flavor parameters in the framework of a warped extra dimension.

We examine decays of a spin-1 bottomonium into a pair of light scalar dark matter (DM) particles, assuming that dark matter is produced due to exchange of heavy degrees of freedom. We perform a model-independent analysis and derive formulae for the branching ratios of these decays. We confront our calculation results with the experimental data. We show that the considered branching ratios are within the reach of the present BABAR experimental sensitivity. Thus, dark matter production in ${\rm Y}$ decays leads to constraints on parameters of various models containing a light spin-0 DM particle. We illustrate this for the models with a “WIMPless miracle”, in particular, for a gauge-mediated SUSY breaking scenario, with a spin-0 DM particle in the hidden sector. Another example considered is the type II two-Higgs doublet model with a scalar DM particle.