We introduce a general characterization of sudden cosmological singularities and investigate the classical stability of homogeneous and isotropic cosmological solutions of all curvatures containing these singularities to small scalar, vector, and tensor perturbations using gauge-invariant perturbation theory. We establish that sudden singularities at which the scale factor, expansion rate, and density are finite are stable except for a set of special parameter values. We also apply our analysis to the stability of Big Rip singularities and find the conditions for their stability against small scalar, vector, and tensor perturbations.

We derive slow-roll conditions for thawing k-essence with a separable Lagrangian $p(X,\varphi )=F(X)V(\varphi )$. We examine the evolution of the equation of state parameter, $w$, as a function of the scale factor $a$, for the case where $w$ is close to $-1$. We find two distinct cases, corresponding to $X\approx 0$ and $F_X\approx 0$, respectively. For the case where $X\approx 0$ the evolution of $\varphi$ and hence $w$ is described by only two parameters, and $w(a)$ is model independent and coincides with similar behavior seen in thawing quintessence models. This result also extends to nonseparable Lagrangians where $X\approx 0$. For the case $F_X\approx 0$, an expression is derived for $w(a)$, but this expression depends on the potential $V(\varphi )$, so there is no model-independent limiting behavior. For the $X\approx 0$ case, we derive observational constraints on the two parameters of the model, $w_0$ (the present-day value of $w$), and the $K$, which parametrizes the curvature of the potential. We find that the observations sharply constrain $w_0$ to be close to $-1$, but provide very poor constraints on $K$.

Hořava-Lifshitz gravity, a recent proposal for a UV-complete renormalizable gravity theory, may lead to a bouncing cosmology. In this article we argue that Hořava-Lifshitz cosmology may yield a concrete realization of the matter bounce scenario and thus give rise to an alternative to inflation for producing a scale-invariant spectrum of cosmological perturbations. In this scenario, quantum vacuum fluctuations exit the Hubble radius in the prebounce phase, and the spectrum is transformed into a scale-invariant one on super-Hubble scales before the bounce because the long wavelength modes undergo squeezing of their wave functions for a longer period of time than shorter wavelength modes. The scale invariance of the spectrum of curvature fluctuations is preserved during and after the bounce. A distinctive prediction of this scenario is the amplitude and shape of the bispectrum.

We propose an accurate method to count states of close to zero and positive cosmological constant in the Bousso-Polchinski Landscape. This method is based on simple geometrical considerations on the high-dimensional lattice of quantized fluxes and on a probabilistic model (the “random hyperplane” model) which provides a distribution of the cosmological constant’s values. Evidence of the assumptions made in this model are offered by means of numerical experiments.

The growth rate of matter perturbations can be used to distinguish between different gravity theories and to distinguish between dark energy and modified gravity at cosmological scales as an explanation to the observed cosmic acceleration. We suggest here parameterizations of the growth index as functions of the redshift. The first one is given by $\gamma (a)=\tilde{\gamma }(a)\frac{1}{1+(a_{\mathrm{ttc}}/a)}+{\gamma }_{\mathrm{early}}\frac{1}{1+(a/a_{\mathrm{ttc}})}$, which interpolates between a low/intermediate redshift parameterization $\tilde{\gamma }(a)={\gamma }_{\mathrm{late}}(a)={\gamma }_0+(1-a){\gamma }_a$ and a high redshift ${\gamma }_{\mathrm{early}}$ constant value. For example, our interpolated form $\gamma (a)$ can be used when including the cosmic microwave background to the rest of the data, while the form ${\gamma }_{\mathrm{late}}(a)$ can be used otherwise. It is found that the parameterizations proposed achieve a fit that is better than 0.004% for the growth rate in a $\Lambda \mathrm{CDM}$ model, better than 0.014% for quintessence-cold-dark-matter models, and better than 0.04% for the flat Dvali-Gabadadze-Porrati model (with ${\Omega }_m^0=0.27$) for the entire redshift range up to $z_{\mathrm{CMB}}$. We find that the growth index parameters $({\gamma }_0,{\gamma }_a)$ take distinctive values for dark energy models and modified gravity models, e.g. $(0.5655,-0.02718)$ for the $\Lambda \mathrm{CDM}$ model and (0.6418, 0.062 61) for the flat Dvali-Gabadadze-Porrati model. This provides a means for future observational data to distinguish between the models.

We consider improving the sensitivity of future interferometric gravitational-wave detectors by simultaneously injecting two squeezed vacuums (light), filtered through a resonant Fabry-Perot cavity, into the dark port of the interferometer. The same scheme with single squeezed vacuum was first proposed and analyzed by Corbitt et al. [Phys. Rev. D 70, 022002 (2004).]. Here we show that the extra squeezed vacuum, together with an additional homodyne detection suggested previously by one of the authors [F. Ya. Khalili, Phys. Rev. D 77, 062003 (2008).], allows reduction of quantum noise over the entire detection band. To motivate future implementations, we take into account a realistic technical noise budget for Advanced LIGO and numerically optimize the parameters of both the filter and the interferometer for detecting gravitational-wave signals from two important astrophysics sources, namely, neutron-star–neutron-star binaries and bursts. Assuming the optical loss of the $\sim 30\mathrm{m}$ filter cavity to be 10 ppm per bounce and 10 dB squeezing injection, the corresponding quantum noise with optimal parameters lowers by a factor of 10 at high frequencies and goes below the technical noise at low and intermediate frequencies.

If dark matter (DM) has nonzero direct or transition, electric or magnetic dipole moment then it can scatter nucleons electromagnetically in direct detection experiments. Using the results from experiments like XENON, CDMS, DAMA, and COGENT, we put bounds on the electric and magnetic dipole moments of DM. If DM consists of Dirac fermions with direct dipole moments, then DM of mass less than 10 GeV is consistent with the DAMA signal and with null results of other experiments. If on the other hand DM consists of Majorana fermions then they can have only nonzero transition moments between different mass eigenstates. We find that Majorana fermions with masses $38\lesssim m_{\chi }\lesssim 100–200\mathrm{GeV}$ and mass splitting of the order of (150–200) keV can explain the DAMA signal and the null observations from other experiments and in addition give the observed relic density of DM by dipole-mediated annihilation. The absence of the heavier DM state in the present Universe can be explained by dipole-mediated radiative decay. This parameter space for the mass and for dipole moments is allowed by limits from L3 but may have observable signals at LHC.

In this paper, we initiate the study of finite temperature quantum field theories on the Moyal plane. Such theories violate causality which influences the properties of these theories. In particular, causality influences the fluctuation-dissipation theorem: as we show, a disturbance in a space-time region $M_1$ creates a response in a space-time region $M_2$ spacelike with respect to $M_1$ ($M_1\times M_2$). The relativistic Kubo formula with and without noncommutativity is discussed in detail, and the modified properties of relaxation time and the dependence of mean square fluctuations on time are derived. In particular, the Sinha-Sorkin result [Phys. Rev. B 45, 8123 (1992)] on the logarithmic time dependence of the mean square fluctuations is discussed in our context. We derive an exact formula for the noncommutative susceptibility in terms of the susceptibility for the corresponding commutative case. It shows that noncommutative corrections in the four-momentum space have remarkable periodicity properties as a function of the four-momentum $k$. They have direction dependence as well and vanish for certain directions of the spatial momentum. These are striking observable signals for noncommutativity. The Lehmann representation is also generalized to any value of the noncommutativity parameter ${\theta }^{\mu \nu }$ and finite temperatures.

In the context of a warped extra dimension with standard model fields in the bulk, we obtain the general flavor structure of the Higgs couplings to fermions. These couplings will be generically misaligned with respect to the fermion mass matrix, producing large and potentially dangerous flavor changing neutral currents. As recently pointed out [K. Agashe and R. Contino, arXiv:0906.1542.], a similar effect is expected from the point of view of a composite Higgs sector, which corresponds to a four-dimensional theory dual to the five-dimensional setup by the AdS/CFT correspondence. We also point out that the effect is independent of the geographical nature of the Higgs (bulk or brane localized), and specifically that it does not go away as the Higgs is pushed towards the IR boundary. The flavor changing neutral currents mediated by a light enough Higgs (especially their contribution to ${ϵ}_K$) could become of comparable size as the ones coming from the exchange of Kaluza-Klein gluons. Moreover, both sources of flavor violation are complementary since they have inverse dependence on the five-dimensional Yukawa couplings, such that we cannot decouple the flavor violation effects by increasing or decreasing these couplings. We also find that for Kaluza-Klein scales of a few TeV, the Higgs couplings to third generation fermions could experience suppressions of up to 40% while the rest of diagonal couplings would suffer much milder corrections. Potential LHC signatures like the Higgs flavor violating decays $h\to \mu \tau$ or $h\to tc$, or the exotic top decay channel $t\to ch$, are finally addressed.

We report the phenomenological impact of unparticles in the production of dijet at the LHC. We compute the scalar, spin-1 and spin-2 unparticle contributions to the dijet cross sections and present our results in different kinematical distributions. We find that the scalar unparticle contribution is dominant over that of the spin-1 and spin-2 unparticles for the same coupling values.

We study the confinement property of the pure SU(3) gauge theory, combining in this effort the nonperturbative gluon and ghost propagators obtained as solutions of Dyson-Schwinger equations with solutions of an integral ladder diagram summation type equation for the Wilson loop. We obtain the string potential and effective UV coupling.

We investigate the thermodynamic properties including equation of state, the trace anomaly, the sound velocity, and the specific heat, as well as transport properties like bulk viscosity in the $Z(2)$ and $O(4)$ models in the Hartree approximation of Cornwall-Jackiw-Tomboulis formalism. We study these properties in different cases, e.g. first-order phase transition, second-order phase transition, crossover and the case without phase transition, and discuss the correlation between the bulk viscosity and the thermodynamic properties of the system. We find that the bulk viscosity over entropy density ratio exhibits an upward cusp at the second-order phase transition, and a sharp peak at the first-order phase transition. However, this peak becomes smooth or disappears in the case of crossover. This result supports the idea that the bulk viscosity over entropy density ratio is a better quantity than the shear viscosity over entropy density ratio to locate the critical end point.

We present a next-to-leading order QCD calculation for $e^{+}{\nu }_e{\mu }^{+}{\nu }_{\mu }jj$ and $e^{-}{\overline{\nu }}_e{\mu }^{-}{\overline{\nu }}_{\mu }jj$ production via weak-boson fusion at a hadron collider in the form of a fully flexible parton-level Monte Carlo program, which allows for the calculation of experimentally accessible observables within realistic selection cuts. The QCD corrections to the integrated cross sections are found to be modest, while the shapes of some kinematical distributions change appreciably compared to leading order. The residual scale uncertainties of the next-to-leading order results are at the few-percent level.

In this paper we present quantitative results for coherent pion production by neutrinos scattered off nuclei within the framework developed by Gounaris, Kartavtsev, and Paschos. The method is based on partially conserved axial-vector current and uses helicity cross sections for the scattering of weak gauge bosons on nuclei. The process relies on experimental data for elastic pion-nucleus scattering. A detailed analysis of the differential and integrated cross sections is presented for neutral and charged currents, with special emphasis on the regions of integrations. The results are extended to energies of 10.0 GeV and are compared with experimental data.

We study a simple framework for gauge-mediated supersymmetry breaking in local grand unified theory (GUT) models based on $F$-theory 7-branes and demonstrate that a mechanism for solving both the $\mu$ and $\mu /B_{\mu }$ problems emerges in a natural way. In particular, a straightforward coupling of the messengers to the Higgs sector leads to a geometry which not only provides us with an approximate $U(1{)}_{\mathrm{PQ}}$ symmetry that forbids the generation of $\mu$ at the GUT scale, it also forces the SUSY-breaking spurion field to carry a nontrivial Peccei-Quinn (PQ) charge. This connects the breaking of supersymmetry (SUSY) to the generation of $\mu$ so that the same scale enters both. Moreover, the messenger sector naturally realizes the $D3$-instanton triggered SUSY-breaking model of [J. Heckman, J. Marsano, N. Saulina, S. Schafer-Nameki, and C. Vafa, arXiv:0808.1286.] so this scale is exponentially suppressed relative to $M_{\mathrm{GUT}}$. The effective action at low scales is in fact precisely of the form of the “sweet spot supersymmetry” scenario studied by Ibe and Kitano in [M. Ibe and R. Kitano, J. High Energy Phys. 08 (2007) 016.].

We study the deconfinement transition of hadronic matter into quark matter under neutron star conditions assuming color and flavor conservation during the transition. We use a two-phase description. For the hadronic phase we use different parametrizations of a nonlinear Walecka model which includes the whole baryon octet. For the quark-matter phase we use an $\mathrm{SU}(3{)}_f$ Nambu–Jona-Lasinio effective model including color superconductivity. Deconfinement is considered to be a first order phase transition that conserves color and flavor. It gives a short-lived transitory colorless-quark phase that is not in $\beta$ equilibrium, and decays to a stable configuration in $\tau \sim {\tau }_{\mathrm{weak}}\sim {10}^{-8}\mathrm{s}$. However, in spite of being very short lived, the transition to this intermediate phase determines the onset of the transition inside neutron stars. We find the transition free-energy density for temperatures typical of neutron star interiors. We also find the critical mass above which compact stars should contain a quark core and below which they are safe with respect to a sudden transition to quark matter. Rather independently on the stiffness of the hadronic equation of state (EOS) we find that the critical mass of hadronic stars (without trapped neutrinos) is in the range of $\sim 1.5–1.8$ solar masses. This is in coincidence with previous results obtained within the MIT bag model.

The gravitational polarizability properties of black holes are compared and contrasted with their electromagnetic polarizability properties. The “shape” or “height” multipolar Love numbers $h_l$ of a black hole are defined and computed. They are then compared to their electromagnetic analogs $h_l^{\mathrm{EM}}$. The Love numbers $h_l$ give the height of the $l$th multipolar “tidal bulge” raised on the horizon of a black hole by faraway masses. We also discuss the shape of the tidal bulge raised by a test-mass $m$, in the limit where $m$ gets very close to the horizon.

We show that, for space-times with inner boundaries, there exists a natural area operator different from the standard one used in loop quantum gravity. This new flux-area operator has equidistant eigenvalues. We discuss the consequences of substituting the standard area operator in the Ashtekar-Baez-Corichi-Krasnov definition of black hole entropy by the new one. Our choice simplifies the definition of the entropy and allows us to consider only those areas that coincide with the one defined by the value of the level of the Chern-Simons theory describing the horizon degrees of freedom. We give a prescription to count the number of relevant horizon states by using spin components and obtain exact expressions for the black hole entropy. Finally we derive its asymptotic behavior, discuss several issues related to the compatibility of our results with the Bekenstein-Hawking area law and the relation with Schwarzschild quasinormal modes.

We study an observational method to analyze non-Gaussianity of a gravitational wave (GW) background made by superposition of weak burst signals. The proposed method is based on fourth-order correlations of data from four detectors, and might be useful to discriminate the origin of a GW background. With a formulation newly developed to discuss geometrical aspects of the correlations, it is found that the method provides us with linear combinations of two interesting parameters, $I_2$ and $V_2$ defined by the Stokes parameters of individual GW burst signals. We also evaluate sensitivities of specific detector networks to these parameters.

Dark matter candidates are natural in technicolor theories. We introduce a general framework allowing to predict signals of technicolor dark matter at colliders and set constraints from Earth-based experiments such as CDMS and XENON. We show that the associate production of the composite Higgs can lead to relevant signals at the Large Hadron Collider.