While the particle hypothesis for dark matter may be very soon investigated at the LHC, and as the PAMELA and GLAST satellites are currently taking new data on charged and gamma cosmic rays, the need of controlling the theoretical uncertainties affecting the possible indirect signatures of dark matter annihilation is of paramount importance. The uncertainties which originate from the dark matter distribution are difficult to estimate because current astrophysical observations provide rather weak dynamical constraints and because, according to cosmological N-body simulations, dark matter is neither smoothly nor spherically distributed in galactic halos. Some previous studies made use of N-body simulations to compute the $\gamma$-ray flux from dark matter annihilation, but such a work has never been performed for the antimatter (positron and antiproton) primary fluxes, for which transport processes complicate the calculations. We take advantage of the galaxylike 3D dark matter map extracted from the Horizon Project results to calculate the positron and antiproton fluxes from dark matter annihilation, in a model-independent approach as well as for dark matter particle benchmarks relevant at the LHC scale (from supersymmetric and extradimensional theories). We find that the flux uncertainties arise mainly from fluctuations of the local dark matter density, and are of $\sim 1$ order of magnitude. We compare our results to analytic descriptions of the dark matter halo, showing how the latter can well reproduce the former. The overall antimatter predictions associated with our benchmark models are shown to lie far below the existing measurements and, in particular, that of the positron fraction recently reported by PAMELA, and far below the background predictions as well. Finally, we stress the limits of the use of an N-body framework in this context.

The possibility of testing spatial noncommutativity by current experiments on normal quantum scales is investigated. In the case of both position-position and momentum-momentum noncommuting the spectra of ions in crossed electric and magnetic fields are studied in the formalism of noncommutative quantum mechanics. In a limit of the kinetic energy approaching its lowest eigenvalue, this system possesses nontrivial dynamics. Signals of spatial noncommutativity in the angular momentum are revealed. They are within limits of the measurable accuracy of current experiments. An experimental test of the predictions using a modified electron momentum spectrum is suggested. The related experimental sensitivity and subtle points are discussed. The results are the first step on a realizable way towards a conclusive test of spatial noncommutativity.

An analytic solution for the accretion of ultrahard perfect fluid onto a moving Kerr-Newman black hole is found. This solution is a generalization of the previously known solution by Petrich, Shapiro, and Teukolsky for a Kerr black hole. We show that the found solution is applicable for the case of a nonextreme black hole, however it cannot describe the accretion onto an extreme black hole due to violation of the test fluid approximation. We also present a stationary solution for a massless scalar field in the metric of a Kerr-Newman naked singularity.

We show that expanding or contracting Kasner universes are unstable due to the amplification of gravitational waves (GW). As an application of this general relativity effect, we consider a preinflationary anisotropic geometry characterized by a Kasner-like expansion, which is driven dynamically towards inflation by a scalar field. We investigate the evolution of linear metric fluctuations around this background, and calculate the amplification of the long-wavelength GW of a certain polarization during the anisotropic expansion (this effect is absent for another GW polarization, and for scalar fluctuations). These GW are superimposed to the usual tensor modes of quantum origin from inflation, and are potentially observable if the total number of inflationary $e$-folds exceeds the minimum required to homogenize the observable universe only by a small margin. Their contribution to the temperature anisotropy angular power spectrum decreases with the multipole $\ell$ as ${\ell }^{-p}$, where $p$ depends on the slope of the initial GW power spectrum. Constraints on the long-wavelength GW can be translated into limits on the total duration of inflation and the initial GW amplitude. The instability of classical GW (and zero-vacuum fluctuations of gravitons) during Kasner-like expansion (or contraction) may have other interesting applications. In particular, if GW become nonlinear, they can significantly alter the geometry before the onset of inflation.

The next-to-leading order QCD corrections are calculated for the pair annihilation of spin-1 dark matter (DM) by dimensionally regularizing both ultraviolet and infrared singularities in the nonrelativistic ($v\ll 1$) limit. The complete $O({\alpha }_s)$ correction is about 8% due to the massless gluon contribution. An extra 5% will be added if there is a new interaction from a massive gluon of approximately the same mass as the DM particle. The next-to-leading order QCD correction could result in a sizable shift to the DM mass constrained by relic density measurements.

We investigate spherically symmetric, static matter configurations with polytropic equation of state for a class of $f(R)$ models in Palatini formalism and show that the surface singularities recently reported in the literature are not physical in the case of Planck scale modified Lagrangians. In such cases, they are just an artifact of the idealized equation of state used. In fact, we show that for the models $f(R)=R\pm \lambda R^2$, with $\lambda$ on the order of the Planck length squared, the presence of a single electron in the Universe would be enough to cure all stellar singularities of this type. From our analysis it also follows that the stellar structure derived from these Lagrangians is virtually undistinguishable from that corresponding to general relativity. For ultraviolet corrected models far from the Planck scale, however, the surface singularities may indeed arise in the region of validity of the polytropic equation of state. This fact can be used to place constraints on the parameters of particular models.

The annihilation of dark matter particles releases energy, ionizing some of the gas in the Universe. We investigate the effect of dark matter halos on reionization. We show that the effect depends on the assumed density profile, the particle mass, and the assumed minimum halo mass. For Navarro-Frenk-White halos and typical WIMPs, we find the effect to be quite small. However, light dark matter candidates in the MeV range can contribute significantly to reionization and can make an important contribution to the measured optical depth. This effect may be used to constrain light dark matter models. We also study the effect of varying the halo density profile on reionization.

We model the cosmic medium as the mixture of a generalized Chaplygin gas and a pressureless matter component. Within a neo-Newtonian approach (in which, different from standard Newtonian cosmology, the pressure enters the homogeneous and isotropic background dynamics) we compute the matter power spectrum. The 2dFGRS data are used to discriminate between unified models of the dark sector (a purely baryonic matter component of roughly 5% of the total energy content and roughly 95% generalized Chaplygin gas) and different models, for which there is separate dark matter, in addition to that accounted for by the generalized Chaplygin gas. Leaving the corresponding density parameters free, we find that the unified models are strongly disfavored. On the other hand, using unified model priors, the observational data are also well described, in particular, for small and large values of the generalized Chaplygin gas parameter $\alpha$. The latter result is in agreement with a recent, more qualitative but fully relativistic, perturbation analysis in [V. Gorini, A. Y. Kamenshchik, U. Moschella, O. F. Piatella, and A. A. Starobinsky, J. Cosmol. Astropart. Phys. 02 (2008) 016.].

We propose a conceptually and computationally simple method to evaluate the neutrinos emitted by supernova remnants using the observed $\gamma$ ray spectrum. The proposed method does not require any preliminary parametrization of the gamma ray flux; the gamma ray data can be used as an input. In this way, we are able to propagate easily the observational errors and to understand how well the neutrino flux and the signal in neutrino telescopes can be constrained by $\gamma$ ray data. We discuss the various possible sources of theoretical and systematical uncertainties (e.g., hadronic modeling, neutrino oscillation parameters, etc.), obtaining an estimate of the accuracy of our calculation. Furthermore, we apply our approach to the supernova remnant RX J1713.7-3946, showing that neutrino emission is very well constrained by the H.E.S.S. $\gamma$ ray data: indeed, the accuracy of our prediction is limited by theoretical uncertainties. The observation of neutrinos from RX J1713.7-3946 seems possible with an exposure of the order of few ${\mathrm{km}}^2\times \mathrm{year}$, provided that the detection threshold in future neutrino telescopes will be not higher than about 1 TeV.

We study the momentum and the quark mass dependence of the axial nucleon to $\Delta (1232)$ transition form factors in the framework of nonrelativistic chiral effective field theory to leading-one-loop order. The outcome of our analysis provides a theoretical guidance for chiral extrapolations of lattice QCD results with dynamical fermions.

We present a measurement of the branching fraction for the Cabibbo- and color-suppressed $B^0\to {\chi }_{c1}{\pi }^0$ decay based on a data sample of $657\times {10}^{6}B\overline{B}$ events collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We observe a signal of $40\pm 9$ events with a significance of $4.7\sigma$ including systematic uncertainties. The measured branching fraction is $\mathcal{B}(B^0\to {\chi }_{c1}{\pi }^0)=(1.12\pm 0.25(\mathrm{stat})\pm 0.12(\mathrm{syst}.))\times {10}^{-5}$.

It is becoming increasingly clear that metastable vacua may play a prominent role in supersymmetry breaking. To date, however, this idea has been realized only in models where nonperturbative dynamics complicates the analysis of metastability. In this paper, we present a simple construction in which metastable vacua occur classically, i.e., at tree level, and in which supersymmetry breaking is sourced by both $D$ terms and $F$ terms. All relevant dynamics is perturbative, and hence calculations of vacuum energies and lifetimes can be performed explicitly. Moreover, we find that our construction can even give rise to multiple nonsupersymmetric vacua which are degenerate. The nontrivial vacuum structure of such models therefore suggests that they can provide a rich arena for future studies of vacuum metastability in supersymmetric field theories. Our results may also have important consequences for $Z^{\prime }$ phenomenology and the string landscape.

We investigate the high-temperature phase of a dilaton flow deformation of the anti-de Sitter/conformal field theory correspondence. We argue that these geometries should be interpreted as the $\mathcal{N}=4$ gauge theory perturbed by a SO(6) invariant scalar mass and that the high-temperature phase is just the well-known anti-de Sitter-Schwarzschild solution. We compute, within supergravity, the resulting Hawking-Page phase transition, which in this model can be interpreted as a deconfining transition in which the vacuum expectation value for the operator $\mathrm{Tr}{F}^2$ dissolves. In the presence of quarks the model also displays a simultaneous chiral symmetry restoring transition with the Goldstone mode and other quark bound states dissolving into the thermal bath.

Using the method of maximal cuts, we obtain a form of the three-loop four-point scattering amplitude of $\mathcal{N}=8$ supergravity in which all ultraviolet cancellations are made manifest. The Feynman loop integrals that appear have a graphical representation with only cubic vertices, and numerator factors that are quadratic in the loop momenta, rather than quartic as in the previous form. This quadratic behavior reflects cancellations beyond those required for finiteness, and matches the quadratic behavior of the three-loop four-point scattering amplitude in $\mathcal{N}=4$ super-Yang-Mills theory. By direct integration we confirm that no additional cancellations remain in the $\mathcal{N}=8$ supergravity amplitude, thus demonstrating that the critical dimension in which the first ultraviolet divergence occurs at three loops is $D_c=6$. We also give the values of the three-loop divergences in $D=7$, 9, 11. In addition, we present the explicitly color-dressed three-loop four-point amplitude of $\mathcal{N}=4$ super-Yang-Mills theory.

We consider the gravitational recoil due to nonreflection-symmetric gravitational wave emission in the context of axisymmetric Robinson-Trautman spacetimes. We show that regular initial data evolve generically into a final configuration corresponding to a Schwarzschild black hole moving with constant speed. For the case of (reflection-)symmetric initial configurations, the mass of the remnant black hole and the total energy radiated away are completely determined by the initial data, allowing us to obtain analytical expressions for some recent numerical results that have appeared in the literature. Moreover, by using the Galerkin spectral method to analyze the nonlinear regime of the Robinson-Trautman equations, we show that the recoil velocity can be estimated with good accuracy from some asymmetry measures (namely the first odd moments) of the initial data. The extension for the nonaxisymmetric case and the implications of our results for realistic situations involving head-on collision of two black holes are also discussed.

The impact of particle production during inflation on the primordial curvature perturbation spectrum is investigated both analytically and numerically. We obtain an oscillatory behavior on small scales, while on large scales the spectrum is unaffected. The amplitude of the oscillations is proportional to the number of coupled fields, their mass, and the square of the coupling constant. The oscillations are due to a discontinuity in the second time derivative of the inflaton, arising from a temporary violation of the slow-roll conditions. A similar effect on the power spectrum should be produced also in other inflationary models where the slow-roll conditions are temporarily violated.

We introduce the concept of multipoint propagators between linear cosmic fields and their nonlinear counterparts in the context of cosmological perturbation theory. Such functions express how a nonlinearly evolved Fourier mode depends on the full ensemble of modes in the initial density field. We identify and resum the dominant diagrams in the large-$k$ limit, showing explicitly that multipoint propagators decay into the nonlinear regime at the same rate as the two-point propagator. These analytic results generalize the large-$k$ limit behavior of the two-point propagator to arbitrary order. We measure the three-point propagator as a function of triangle shape in numerical simulations and confirm the results of our high-$k$ resummation. We show that any $n$-point spectrum can be reconstructed from multipoint propagators, which leads to a physical connection between nonlinear corrections to the power spectrum at small scales and higher-order correlations at large scales. As a first application of these results, we calculate the reduced bispectrum at one loop in renormalized perturbation theory and show that we can predict the decrease in its dependence on triangle shape at redshift zero, when standard perturbation theory is least successful.

The space-borne antimatter experiment PAMELA has recently reported a surprising rise in the positron to electron ratio at high energies. It has also recently been found that electromagnetic radiative corrections in some cases may boost the gamma-ray yield from supersymmetric dark-matter annihilations in the galactic halo by up to 3 or 4 orders of magnitude, providing distinct spectral signatures for indirect dark matter searches to look for. Here, we investigate whether the same type of corrections can also lead to sizeable enhancements in the positron yield. We find that this is indeed the case, albeit for a smaller region of parameter space than for gamma rays; selecting models with a small mass difference between the neutralino and sleptons, like in the stau-coannihilation region in mSUGRA, the effect becomes more pronounced. The resulting, rather hard positron spectrum with a relatively sharp cutoff may potentially fit the rising positron ratio measured by the PAMELA satellite. To do so, however, very large “boost factors” have to be invoked that are not expected in current models of halo structure. If the predicted cutoff would also be confirmed by later PAMELA data or upcoming experiments, one could either assume nonthermal production in the early universe or nonstandard halo formation to explain such a spectral feature as an effect of dark-matter annihilation. At the end of the paper, we briefly comment on the impact of radiative corrections on other annihilation channels, in particular, antiprotons and neutrinos.

Single-field models of inflation are analyzed in light of the WMAP five-year data. Assuming instantaneous reheating, we find that modular/new inflation models with small powers in the effective inflaton self-interaction are more strongly constrained than previously. The model with a cubic power lies outside the $2\sigma$ regime when the number of e-folds is $\mathcal{N}\le 60$. We also find that the predictions for the intermediate model of inflation do not overlap the $1\sigma$ region regardless of the power of the monomial potential. We analyze a number of ultraviolet, Dirac-Born-Infeld braneworld scenarios involving both wrapped and multiple-brane configurations, where the inflaton kinetic energy is close to the maximum allowed by the warped geometry. In all cases, we find that the parameters of the warped throat are strongly constrained by observations.

A number of positive and null results on the time variation of fundamental constants have been reported. It is difficult to judge whether or not these claims are mutually consistent, since the observable quantities depend on several parameters, namely, the coupling strengths and masses of particles. The evolution of these coupling-parameters over cosmological history is also a priori unknown. A direct comparison requires a relation between the couplings. We explore several distinct scenarios based on unification of gauge couplings, providing a representative (though not exhaustive) sample of such relations. For each scenario we obtain a characteristic time dependence and discuss whether a monotonic time evolution is allowed. For all scenarios, some contradictions between different observations appear. We show how a clear observational determination of nonzero variations would test the dominant mechanism of varying couplings within unified theories.