We study observational constraints on models that account for the accelerated expansion of the universe via infrared modifications to general relativity, namely, the Dvali-Gabadadze-Porrati braneworld model as well as the Dvali-Turner and Cardassian models. We find that significant constraints can be placed on the parameters of each model using type Ia supernovae data together with the baryon acoustic peak in the large-scale correlation function of the Sloan Digital Sky Survey of luminous red galaxies and the Cosmic Microwave Background Radiation shift parameter data. Moreover, by considering the Poincaré dodecahedral space as the circles-in-the-sky observable spatial topology, we show that the detection of a such a nontrivial topology would provide relevant additional constraints, particularly on the curvature parameter, for all models.

The production of pairs of doubly charged vector bileptons is studied at future $\gamma \gamma$ colliders. The unpolarized cross section for the $\gamma \gamma \to Y^{--}{Y}^{++}$ subprocess is analytically calculated and convoluted to predict the number of events in the complete $e^{+}{e}^{-}\to \gamma \gamma \to Y^{--}{Y}^{++}$ process. The gauge or nongauge character of the vector bilepton $Y^{\pm \pm }$ is discussed. It is found that, as a consequence of its spectacular signature, as it decays dominantly into two identical charged leptons, and also due to its charge contents, which significantly enhance the cross section, the detection of this class of particles with mass in the sub-TeV region can be at the reach of these colliders. The model-independent nature of our results is stressed.

If the lowest lying Kaluza-Klein states in Randall-Sundrum (RS1) models have masses in the 10–100 TeV range, direct production of these states at the LHC or ILC is impossible, and electroweak precision measurements may not be sufficiently sensitive. We address the possibility that high-precision measurements of top pair production at the ILC may provide the first evidence of these states. We consider RS1 models with fermions on and off the brane, with bulk left and right-handed mass terms, discuss brane kinetic terms and calculate corrections to top pair production in these models.

Perturbative expansions of several small Wilson loops are computed through next-to-next-to-leading order in unquenched lattice QCD, from Monte Carlo simulations at weak couplings. This approach provides a much simpler alternative to conventional diagrammatic perturbation theory, and is applied here for the first time to full QCD. Two different sets of lattice actions are considered: one set uses the unimproved plaquette gluon action together with the unimproved-staggered-quark action; the other set uses the one-loop-improved Symanzik gauge-field action together with the so-called asqtad improved-staggered-quark action. Simulations are also done with different numbers of dynamical fermions. An extensive study of the systematic uncertainties is presented, which demonstrates that the small third-order perturbative component of the observables can be reliably extracted from simulation data. We also investigate the use of the rational hybrid Monte Carlo algorithm for unquenched simulations with unimproved-staggered fermions. Our results are in excellent agreement with diagrammatic perturbation theory, and provide an important cross-check of the perturbation theory input to a recent determination of the strong coupling ${\alpha }_{\overline{\mathrm{MS}}}(M_Z)$ by the HPQCD collaboration.

We perform a study of the quark-gluon vertex function with a quenched Wilson gauge action and a variety of fermion actions. These include the domain wall fermion action (with exponentially accurate chiral symmetry) and the Wilson clover action both with the nonperturbatively improved clover coefficient as well as with a number of different values for this coefficient. We find that the domain wall vertex function behaves very well in the large-momentum-transfer region. The off-shell vertex function for the on-shell improved clover class of actions does not behave as well as the domain wall case and, surprisingly, shows only a weak dependence on the clover coefficient $c_{\mathrm{SW}}$ for all components of its Dirac decomposition and across all momenta. Including off-shell improvement rotations for the clover fields can make this action yield results consistent with those from the domain wall approach, as well as helping to determine the off-shell improved coefficient $c_q^{\prime }$.

We derive factorization relations for the transverse helicity amplitudes in $B\to K\pi {\ell }^{+}{\ell }^{-}$ at leading order in $\Lambda /m_b$, in the kinematical region with an energetic kaon and a soft pion. We identify and compute a new contribution of leading order in $\Lambda /m_b$ to the $B\to K\pi {\ell }^{+}{\ell }^{-}$ amplitude which is not present in the one-body decay $B\to K^{*}{\ell }^{+}{\ell }^{-}$. As an application we study the forward-backward asymmetry (FBA) of the lepton momentum angular distribution in $B\to K\pi {\ell }^{+}{\ell }^{-}$ decays on and off the $K^{*}$ resonance. The FBA in these decays has a zero at $q_0^2=q_0^2(M_{K\pi })$, which can be used, in principle, for determining the Wilson coefficients $C_{7,9}$ and testing the standard model. We point out that the slope of the $q_0^2(M_{K\pi }^2)$ curve contains the same information about the Wilson coefficients as the location of the zero, but is less sensitive to unknown nonperturbative dynamics. We estimate the location of the zero at leading order in factorization, and using a resonant model for the $B\to K\pi {\ell }^{+}{\ell }^{-}$ nonfactorizable amplitude.

Method of polarized semi-inclusive deep inelastic scattering (SIDIS) data analysis in the next to leading order (NLO) QCD is developed. Within the method one first directly extracts in NLO few first truncated (available to measurement) Mellin moments of the quark helicity distributions. Second, using these moments as an input to the proposed modification of the Jacobi polynomial expansion method (MJEM), one eventually reconstructs the local quark helicity distributions themselves. All numerical tests demonstrate that MJEM allows us to reproduce with the high precision the input local distributions even inside the narrow Bjorken $x$ region accessible for experiment. It is of importance that only four first input moments are sufficient to achieve a good quality of reconstruction. The application of the method to the simulated SIDIS data on the pion production is considered. The obtained results encourage one that the proposed NLO method can be successfully applied to the SIDIS data analysis. The analysis of HERMES data on pion production is performed. To this end the pion difference asymmetries are constructed from the measured by HERMES standard semi-inclusive spin asymmetries. The LO results of the valence distribution reconstruction are in a good accordance with the respective leading order SMC and HERMES results, while the NLO results are in agreement with the existing NLO parametrizations on these quantities.

The Coulomb problem for vector bosons $W^{\pm }$ incorporates a well-known difficulty; the charge of the boson localized in a close vicinity of the attractive Coulomb center proves to be infinite. The paradox is shown to be resolved by the QED vacuum polarization, which brings in a strong effective repulsion that eradicates the infinite charge of the boson on the Coulomb center. This property allows one to define the Coulomb problem for vector bosons properly.

If the lepton mixing angle ${\theta }_{23}$ is not maximal, there arises a problem of ambiguity in determining ${\theta }_{23}$ due to the existence of two degenerate solutions, one in the first and the other in the second octant. We discuss an experimental strategy for resolving the ${\theta }_{23}$ octant degeneracy by combining reactor measurement of ${\theta }_{13}$ with accelerator ${\nu }_{\mu }$ disappearance and ${\nu }_e$ appearance experiments. The robustness of the ${\theta }_{23}$ degeneracy and the difficulty in lifting it only by accelerator experiments with conventional ${\nu }_{\mu }$ (and ${\overline{\nu }}_{\mu }$) beams are demonstrated by analytical and numerical treatments. Our method offers a way to overcome the difficulty and can resolve the degeneracy between solutions ${sin}^2{\theta }_{23}=0.4$ and ${sin}^2{\theta }_{23}=0.6$ if ${sin}^{2}2{\theta }_{13}\gtrsim 0.05$ at 95% CL by assuming the T2K phase II experiment and a reactor measurement with an exposure of 10 GW·kt·yr. The dependence of the resolving power of the octant degeneracy on the systematic errors of reactor experiments is also examined.

We provide a simple mathematical description of the exchange of energy between two fluids in an expanding Friedmann universe with zero spatial curvature. The evolution can be reduced to a single nonlinear differential equation which we solve in physically relevant cases and provide an analysis of all the possible evolutions. Particular power-law solutions exist for the expansion scale factor and are attractors at late times under particular conditions. We show how a number of problems studied in the literature, such as cosmological vacuum-energy decay, particle annihilation, and the evolution of a population of evaporating black holes, correspond to simple particular cases of our model. In all cases we can determine the effects of the energy transfer on the expansion scale factor. We also consider the situation in the presence of “antidecaying” fluids and so-called “phantom” fluids which violate the dominant energy conditions.

The Collins fragmentation function is extracted from HERMES data on azimuthal single spin asymmetries in semi-inclusive deeply inelastic scattering, and BELLE data on azimuthal asymmetries in $e^{+}{e}^{-}$-annihilations. A Gaussian model is assumed for the distribution of transverse parton momenta and predictions are used from the chiral quark-soliton model for the transversity distribution function. We find that the HERMES and BELLE data yield a consistent picture of the Collins fragmentation function which is compatible with COMPASS data and the information previously obtained from an analysis of DELPHI data. Estimates for future experiments are made.

We construct M theory on the orbifold ${\mathbb{C}}^2/{\mathbb{Z}}_N$ by coupling 11-dimensional supergravity to a seven-dimensional Yang-Mills theory located on the orbifold fixed plane. It is shown that the resulting action is supersymmetric to leading nontrivial order in the 11-dimensional Newton constant. This action provides the starting point for a reduction of M theory on $G_2$ spaces with codimension four singularities.

The masses of several recently-constructed rotating black holes in gauged supergravities, including the general such solution in minimal gauged supergravity in five dimensions, have until now been calculated only by integrating the first law of thermodynamics. In some respects it is more satisfactory to have a calculation of the mass that is based directly upon the integration of a conserved quantity derived from a symmetry principal. In this paper, we evaluate the masses for the newly-discovered rotating black holes using the conformal definition of Ashtekar, Magnon and Das (AMD), and show that the results agree with the earlier thermodynamic calculations. We also consider the Abbott-Deser (AD) approach, and show that this yields an identical answer for the mass of the general rotating black hole in five-dimensional minimal gauged supergravity. In other cases we encounter discrepancies when applying the AD procedure, which can be resolved by including a contribution from the energy of the scalar fields. The AMD approach, involving no decomposition into background plus deviation, is not subject to such complications. Finally, we also calculate the Euclidean action for the five-dimensional solution in minimal gauged supergravity, showing that it is consistent with the quantum statistical relation.

Cosmic horizons arise in general relativity in the context of black holes and in certain cosmologies. Classically, regions beyond a horizon are inaccessible to causal observers. However, quantum mechanical correlations may exist across horizons that may influence local observations. For the case of de Sitter space, we show how a single particle excitation behind the horizon changes the density matrix governing local observables. As compared to the vacuum state, we calculate the change in the average energy and entropy per unit volume. This illustrates what may be a generic property allowing some features of spacetime beyond a horizon to be inferred.

Current strategies of indirect dark matter detection with neutrino telescopes are based on the search for high-energy neutrinos from the solar core or from the center of the Earth. Here, we propose a new strategy based on the detection of neutrinos from dark matter annihilations in mini-spikes around intermediate mass black holes. Neutrino fluxes, in this case, depend on the annihilation cross-section of dark matter particles, whereas solar and terrestrial fluxes are sensitive to the scattering cross-section off nucleons, a circumstance that makes the proposed search complementary to the existing ones. We discuss the prospects for detection with upcoming underwater and under-ice experiments such as ANTARES and IceCube, and show that several, up to many, sources could be detected with both experiments. A kilometer-scale telescope in the Mediterranean appears to be ideally suited for the proposed search.

The bulk of the extragalactic background between 10 keV and 10 GeV is likely to be explained by the emission of Seyfert galaxies, type Ia supernovae, and blazars. However, as revealed by the INTEGRAL satellite, the bulge of our galaxy is an intense source of a 511 keV gamma-ray line, indicating the production of a large number of positrons that annihilate. The origin of the latter is debated, and they could be produced, in particular, by the ($S$- or $P$-wave) annihilation of light dark matter particles into $e^{+}{e}^{-}$. In any case, the cumulated effect of similar sources at all redshifts could lead to a new background of hard x-ray and soft gamma-ray photons. On the basis of the hierarchical model of galaxy formation, we compute analytically the SNIa contribution to the background, and add it to Seyfert and blazars emission models. Confronting these expected contributions to observation, we find that any extra contribution to this unresolved background around 511 keV should be lower than about $4\mathrm{keV}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}{\mathrm{sr}}^{-1}$. We also estimate analytically the extragalactic background due to dark matter annihilation, increasing the accuracy of the earlier computations. Indeed, we take into account the large positron escape fraction from low mass dark matter halos, unable to confine a dense and magnetized interstellar medium. Our new background estimate turns out to be 1 order of magnitude lower so that the hypothesis of a light dark matter candidate remains compatible with the observed extragalactic background for a wider range of particle masses and cross sections.

It is shown that in the large-$N_c$ limit radial, Regge trajectories give rise in a natural way to the presence of the dimension-2 gluon condensate $⟨A^2⟩$ in meson correlators. We match these models to QCD and provide estimates for $⟨A^2⟩$ in terms of other physical quantities. In particular, in the simplest strictly linear radial Regge model with equal residues $⟨A^2⟩$ is proportional to the pion decay constant squared. However, the linear model fails a consistency condition based on matching the short- and long-distance string tensions, nor does it reproduce the phenomenological values of the gluon condensates. On the contrary, in Regge models departing from strict linearity one may reproduce both the consistency condition and the signs of condensates. We demonstrate this in a simple explicit model.

The multiple point principle (MPP) is applied to the nonsupersymmetric two-Higgs doublet extension of the standard model (SM). The existence of a large set of degenerate vacua at some high energy scale caused by the MPP results in a few relations between Higgs self-coupling constants which can be examined at future colliders. The numerical analysis reveals that these MPP conditions constrain the mass of the SM-like Higgs boson to lie below 180 GeV for a wide set of MPP scales $\Lambda$ and $\tan \beta$.

We investigate nucleosynthesis in the supernova post-core bounce neutrino-driven wind environment in the presence of active-sterile neutrino transformation. We consider active-sterile neutrino oscillations for a range of mixing parameters: vacuum mass-squared differences of $0.1{\mathrm{eV}}^2\le \delta m^2\le 100{\mathrm{eV}}^2$, and vacuum mixing angles of ${sin}^{2}2{\theta }_v\ge {10}^{-4}$. We find a consistent $r$-process pattern for a large range of mixing parameters that is in rough agreement with the halo star CS 22892-052 abundances and the pattern shape is determined by fission cycling. We find that the allowed region for the formation of the $r$-process peaks overlaps the liquid scintillator neutron detector (LSND) and null-short baseline (NSBL) ($3+1$) allowed region.

We report on a search for the free-decay component of ${\pi }^{-}$ stopped in water and light materials. A nonzero value of this would be an indication of anomalous ${\overline{\nu }}_e$ contamination to the ${\nu }_e$ and ${\overline{\nu }}_{\mu }$ production at stopped-pion neutrino facilities. No free-decay component of ${\pi }^{-}$ was observed in water, Beryllium, and Aluminum, for which upper limits were established at $8.2\times {10}^{-4}$, $3.2\times {10}^{-3}$, and $7.7\times {10}^{-3}$, respectively.