We construct exact solutions to five-dimensional Einstein-Maxwell theory based on Atiyah-Hitchin space. The solutions cannot be written explicitly in a closed form, so their properties are investigated numerically. The five-dimensional metric is regular everywhere except on the location of the original bolt in four-dimensional Atiyah-Hitchin base space. On each time-fixed slice, the metric asymptotically approaches a Euclidean Taub-NUT space.

Geodesic motion determines important features of spacetimes. Null unstable geodesics are closely related to the appearance of compact objects to external observers and have been associated with the characteristic modes of black holes. By computing the Lyapunov exponent, which is the inverse of the instability time scale associated with this geodesic motion, we show that, in the eikonal limit, quasinormal modes of black holes in any dimensions are determined by the parameters of the circular null geodesics. This result is independent of the field equations and only assumes a stationary, spherically symmetric and asymptotically flat line element, but it does not seem to be easily extendable to anti-de Sitter spacetimes. We further show that (i) in spacetime dimensions greater than four, equatorial circular timelike geodesics in a Myers-Perry black-hole background are unstable, and (ii) the instability time scale of equatorial null geodesics in Myers-Perry spacetimes has a local minimum for spacetimes of dimension $d\ge 6$.

Dark energy and dark matter are only indirectly measured via their gravitational effects. It is possible that there is an exchange of energy within the dark sector, and this offers an interesting alternative approach to the coincidence problem. We consider two broad classes of interacting models where the energy exchange is a linear combination of the dark sector densities. The first class has been previously investigated, but we define new variables and find a new exact solution, which allows for a more direct, transparent, and comprehensive analysis. The second class has not been investigated in general form before. We give general conditions on the parameters in both classes to avoid unphysical behavior (such as negative energy densities).

We prove that the anisotropic inflationary background of the Ackerman-Carroll-Wise model, characterized by a fixed-norm vector field, is unstable. We found the instability by explicitly solving the linearized equations for the most general set of perturbations around this background, and by noticing that the solutions diverge close to horizon crossing. This happens because one perturbation becomes a ghost at that moment. A simplified computation, with only the perturbations of the vector field included, shows the same instability, clarifying the origin of the problem. We then discuss several other models, with a particular emphasis on the case of a nonminimal coupling to the curvature, in which vector fields are used either to support an anisotropic expansion, or to generate cosmological perturbations on an isotropic background. In many cases, the mass squared of the vector needs to be negative; we show that, as a consequence, the longitudinal vector mode is a ghost (a field with negative kinetic term, and negative energy, and not simply a tachyon). We comment on problems that arise at the quantum level. In particular, the presence of a ghost can be a serious difficulty for the UV completion that such models require in the subhorizon regime.

We examine the accuracy of the growth equation $\ddot{\delta }+2H\dot{\delta }-4\pi G\rho \delta =0$, which is ubiquitous in the cosmological literature, in the context of the Newtonian gauge. By comparing the growth predicted by this equation to a numerical solution of the linearized Einstein equations in the $\Lambda \mathrm{CDM}$ scenario, we show that while this equation is a reliable approximation on small scales ($k\gtrsim h{\mathrm{Mpc}}^{-1}$), it can be disastrously inaccurate ($\sim {10}^4\%$) on larger scales in this gauge. We propose a modified version of the growth equation for the Newtonian gauge, which while preserving the simplicity of the original equation, provides considerably more accurate results. We examine the implications of the failure of the growth equation on a few recent studies, aimed at discriminating general relativity from modified gravity, which use this equation as a starting point. We show that while the results of these studies are valid on small scales, they are not reliable on large scales or high redshifts, if one works in the Newtonian gauge. Finally, we discuss the growth equation in the synchronous gauge and show that the corrections to the Poisson equation are exactly equivalent to the difference between the overdensities in the synchronous and Newtonian gauges.

We show that a class of bigravity theories contain solutions describing dark matter. A particular member of this class is also shown to be equivalent to the Eddington-Born-Infeld gravity, recently proposed as a candidate for dark matter. Bigravity theories also have cosmological de Sitter backgrounds and we find solutions interpolating between matter and acceleration eras.

The modified gravity with $F(R,G)$ Lagrangian, $G$ is the Gauss-Bonnet invariant, is considered. It is shown that the phantom-divide-line crossing and the deceleration to acceleration transition generally occur in these models. Our results coincide with the known results of $f(R)$-gravity and $f(G)$-gravity models. The contribution of quantum effects to these transitions is calculated, and it is shown that in some special cases where there are no transitions in classical level, quantum contributions can induce transitions. The quantum effects are described via the account of conformal anomaly.

Ultra-high energy cosmic rays accelerated in astrophysical objects produce secondary electromagnetic cascades during propagation in the cosmic microwave and infrared backgrounds. We show that if the primary cosmic rays are dominated by protons, such cascades can contribute between $\simeq 1\%$ and $\simeq 50\%$ of the GeV-TeV diffuse photon flux measured by the EGRET experiment. The Fermi Gamma-ray Space Telescope (GLAST) should have a good chance to discover this flux. If most ultra-high energy cosmic rays consist of heavy nuclei, the secondary GeV-TeV diffuse photon flux can be lower by factors of several compared to pure proton primaries from the same sources. The diffuse photon flux then depends on the unknown composition of accelerated particles, their maximum energy, and the source distribution.

We present a search for point sources of high energy neutrinos using 3.8 yr of data recorded by AMANDA-II during 2000–2006. After reconstructing muon tracks and applying selection criteria designed to optimally retain neutrino-induced events originating in the northern sky, we arrive at a sample of 6595 candidate events, predominantly from atmospheric neutrinos with primary energy 100 GeV to 8 TeV. Our search of this sample reveals no indications of a neutrino point source. We place the most stringent limits to date on $E^{-2}$ neutrino fluxes from points in the northern sky, with an average upper limit of $E^2{\Phi }_{{\nu }_{\mu }+{\nu }_{\tau }}\le 5.2\times {10}^{-11}\mathrm{TeV}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ on the sum of ${\nu }_{\mu }$ and ${\nu }_{\tau }$ fluxes, assumed equal, over the energy range from 1.9 TeV to 2.5 PeV.

We propose a dark matter (DM) scenario in an extension of a left-right symmetric model with a gauge-singlet scalar field. The gauge-singlet scalar can automatically become a DM candidate, provided that both $P$ and $CP$ symmetries are only broken spontaneously. Thus no extra discrete symmetries are needed to make the DM candidate stable. After constraining the model parameters from the observed relic DM density we make predictions for direct detection experiments. We show that for some parameter range, the predicted weakly interacting massive particle-nucleon elastic scattering cross section can reach the current experimental upper bound, which can be tested by the experiments in the near future.

The next-to-minimal supersymmetric model with a light doubletlike $CP$-odd Higgs boson and small $\tan \beta$ can satisfy all experimental limits on Higgs bosons even with light superpartners. In these scenarios, the two lightest $CP$-even Higgs bosons, $h_1$ and $h_2$, and the charged Higgs boson, $h^{+}$, can all be light enough to be produced at CERN LEP and yet have decays that have not been looked for or are poorly constrained by existing collider experiments. The channel $h_1\to a_1{a}_1$ with $a_1\to {\tau }^{+}{\tau }^{-}$ or $2j$ is still awaiting LEP constraints for $m_{h_1}>86$ or 82 GeV, respectively. LEP data may also contain $e^{+}{e}^{-}\to h_2{a}_1$ events where $h_2\to Z{a}_1$ is the dominant decay, a channel that was never examined. Decays of the charged Higgs bosons are often dominated by $H^{\pm }\to W^{\pm (\star )}{a}_1$ with $a_1\to gg$, $c\overline{c}$, and ${\tau }^{+}{\tau }^{-}$. This is a channel that has so far been ignored in the search for $t\to h^{+}b$ decays at the Tevatron. A specialized analysis might reveal a signal. The light $a_1$ might be within the reach of $B$ factories via ${\rm Y}\to \gamma a_1$ decays. We study typical mass ranges and branching ratios of Higgs bosons in this scenario and compare these scenarios where the $a_1$ has a large doublet component to the more general scenarios with arbitrary singlet component for the $a_1$.

We study the Higgs boson decays and production via gluon fusion at the LHC as a probe of two typical littlest Higgs models which introduce a top quark partner with different (even and odd) $T$ parity to cancel the Higgs mass quadratic divergence contributed by the top quark. For each model, we consider two different choices for the down-type quark Yukawa couplings. We first examine the branching ratios of the Higgs boson decays and then study the production via gluon fusion followed by the decay into two photons or two weak gauge bosons. We find that the predictions can be quite different for different models or different choices of down-type quark Yukawa couplings, and all these predictions can sizably deviate from the standard model predictions. So the Higgs boson processes at the LHC can be a sensitive probe for these littlest Higgs models.

The Sivers distributions recently extracted from semi-inclusive deep inelastic scattering data [M. Anselmino et al., Eur. Phys. J. A 39, 89 (2009)] are used to compute estimates for Sivers asymmetries in Drell-Yan processes which are being planned at several facilities (RHIC, COMPASS, J-PARC, PAX, PANDA, NICA (JINR) and SPASCHARM (IHEP)). Most of these asymmetries turn out to be large and could allow a clear test of the predicted sign change of the Sivers distributions when active in SIDIS and Drell-Yan processes. This is regarded as a fundamental test of our understanding, within QCD and the factorization scheme, of single spin asymmetries.

Recently H. Georgi has introduced the concept of unparticles in order to describe the low energy physics of a nontrivial scale invariant sector of an effective theory. We investigate its physical effects on the neutrino flux to be detected in a kilometer cubic neutrino telescope such as IceCube. We study the effects, on different observables, of the survival neutrino flux after through the Earth, and the regeneration originated in the neutral currents. We calculate the contribution of unparticle physics to the neutrino-nucleon interaction and, then, to the observables in order to evaluate detectable effects in IceCUbe. Our results are compared with the bounds obtained by other nonunderground experiments. Finally, the results are presented as an exclusion plot in the relevant parameters of the new physics stuff.

A search for new physics using three-lepton (trilepton) data collected with the CDF II detector and corresponding to an integrated luminosity of 976 ${\mathrm{pb}}^{-1}$ is presented. The standard model predicts a low rate of trilepton events, which makes some supersymmetric processes, such as chargino-neutralino production, measurable in this channel. The $\mu \mu +\ell$ signature is investigated, where $\ell$ is an electron or a muon, with the additional requirement of large missing transverse energy. In this analysis, the lepton transverse momenta with respect to the beam direction ($p_T$) are as low as $5\mathrm{GeV}/c$, a selection that improves the sensitivity to particles that are light as well as to ones that result in leptonically decaying tau leptons. At the same time, this low-$p_T$ selection presents additional challenges due to the non-negligible heavy-quark background at low lepton momenta. This background is measured with an innovative technique using experimental data. Several dimuon and trilepton control regions are investigated, and good agreement between experimental results and standard-model predictions is observed. In the signal region, we observe one three-muon event and expect $0.4\pm 0.1\mu \mu +\ell$ events from standard-model processes.

The decay $B^0\to D{K}^{*0}$ is well known to provide excellent potential for a precise measurement of the unitarity triangle angle $\gamma$ in future experiments. It is noted that the sensitivity can be significantly enhanced by studying the amplitudes relative to those of the flavor-specific decay $B^0\to D_2^{*-}{K}^{+}$, which can be achieved by analyzing the $B^0\to D{\pi }^{-}{K}^{+}$ Dalitz plot.

We propose a method for determining ultraviolet divergences in the vacuum energy for systems whose spectrum of perturbations is defined through a nonlinear spectrum problem, i.e., when the fluctuation operator itself depends on the frequency. The method is applied to the plasma shell model, which describes some properties of the interaction of electromagnetic field with fullerenes. We formulate a scalar model, which simplifies the matrix structure, but keeps the frequency dependence of the plasma shell, and calculate the ultraviolet divergences in the case when the plasma sheet is slightly curved. The divergent terms are expressed in terms of surface integrals of corresponding invariants.

Exact consistent gravitational anomalies for chiral bosons in two dimensions are treated both with the Schwinger-DeWitt regularization and independently through a cohomological procedure. The diffeomorphism transformations are described by a single ghost which allows one to climb the cohomological chain in a unique way.

In this paper, we compute the mass and the temperature of the uncharged black holes of third order Lovelock gravity as well as the entropy using the first law of thermodynamics. We perform a stability analysis by studying the curves of the temperature versus the mass parameter, and find that an intermediate thermodynamically unstable phase exists for black holes with a hyperbolic horizon. This unstable phase for the uncharged topological black holes of third order Lovelock gravity does not exist in lower order Lovelock gravity. We also perform a stability analysis for a spherical, seven-dimensional black hole of Lovelock gravity and find that, while these kinds of black holes for small values of Lovelock coefficients have an intermediate unstable phase, they are stable for large values of Lovelock coefficients. We also find that an intermediate unstable phase exists for these black holes in higher dimensions. This analysis shows that the thermodynamic stability of black holes with curved horizons is not a robust feature of all the generalized theories of gravity.

This is a study of a monochromatic planar perturbation impinging upon a canonical acoustic hole. We show that acoustic hole scattering shares key features with black hole scattering. The interference of wave fronts passing in opposite senses around the hole creates regular oscillations in the scattered intensity. We examine this effect by applying a partial wave method to compute the differential scattering cross section for a range of incident wavelengths. We demonstrate the existence of a scattering peak in the backward direction, known as the glory. We show that the glory created by the canonical acoustic hole is approximately 170 times less intense than the glory created by the Schwarzschild black hole, for equivalent horizon-to-wavelength ratios. We hope that direct experimental observations of such effects may be possible in the near future.