We investigate a flat Friedmann-Robertson-Walker spacetime filled with k essence and find the set of functions F that generate three different families of extended tachyon fields and Chaplygin gases. They lead to accelerated and superaccelerated expanding scenarios. For any function F, we find the first integral of the k-field equation when the k field is driven by an inverse square potential or by a constant one. In the former, we obtain the general solution of the coupled Einstein–k-field equations for a linear function F. This model shares the same kinematics of the background geometry with the ordinary scalar field one driven by an exponential potential. However, they are dynamically different. For a constant potential, we introduce a k-field model that exhibits a transition from a power-law phase to a de Sitter stage, inducing a modified Chaplygin gas.

We investigate cosmologies where dark matter (DM) is coupled to dark energy (DE), through N-body simulations. The dark-dark coupling introduces two novel effects in particle dynamics: (i) DM particle masses vary with time; (ii) gravity between DM particles is ruled by a constant $G^{*},$ greater than Newton’s constant G, holding in other two-body interactions. Hence, DM particle dynamics violates the equivalence principle and, as a consequence, baryons and DM particle distributions develop a large scale bias. Here we focus on DE models with Ratra-Peebles (RP) potentials. The dark-dark coupling is set in a parametric range compatible with background and linear dynamics. We find that nonlinear dynamics puts additional constraints on the coupling parameter. They mostly arise from cluster density profiles that we find to yield higher concentrations in coupled RP models, with respect to (uncoupled) dynamical DE cosmologies. Such an enhancement, although being a strong effect in some coupling parameter range, leads to acceptable observables for a significant range of values of the coupling parameter. We also analyze the expected cluster mass function and the DM-baryon bias in nonlinear conditions, finding them compatible with data. With the above restrictions, coupled DE models with a RP potential are therefore consistent with cosmological nonlinear observables. As a general conclusion, we confirm that cosmologies with a suitable dark-dark coupling are viable theories.

We combine the most recent observations of large-scale structure (2dF and SDSS galaxy surveys) and cosmic microwave anisotropies (WMAP and ACBAR) to put constraints on flat cosmological models where the number of massive neutrinos and of massless relativistic relics are both left arbitrary. We discuss the impact of each data set and of various priors on our bounds. For the standard case of three thermalized neutrinos, we find $\sum m_{\nu }<1.0\mathrm{}$ (respectively, 0.6) eV (at $2\sigma ),$ using only CMB and LSS data (respectively, including priors from supernova data and the HST Key Project), a bound that is quite insensitive to the splitting of the total mass between the three species. When the total number of neutrinos or relativistic relics, $N_{\mathrm{eff}},$ is left free, the upper bound on $\sum m_{\nu }$ (at $2\sigma ,$ including all priors) ranges from 1.0 to 1.5 eV depending on the mass splitting. We provide an explanation of the parameter degeneracy that allows larger values of the masses when $N_{\mathrm{eff}}$ increases. Finally, we show that the limit on the total neutrino mass is not significantly modified in the presence of primordial gravitational waves, because current data provide a clear distinction between the corresponding effects.

Applying the microcanonical definition of entropy to a weakly interacting and self-gravitating neutralino gas, we evaluate the change in the local entropy per particle of this gas between the freeze-out era and present day virialized halo structures. An “entropy consistency” criterion emerges by comparing theoretical and empirical estimates of this entropy. We apply this criterion to the cases when neutralinos are mostly B-inos and mostly Higgsinos, in conjunction with the usual “abundance” criterion requiring that present neutralino relic density complies with $0.2<\mathrm{}{\Omega }_{{\tilde{\chi }}_1^0}<0.4\mathrm{}$ for $h\simeq \mathrm{0.65.}$ The joint application of both criteria reveals that a much better fitting occurs for the B-ino than for the Higgsino channels, so that the former seems to be a favored channel in the mass range of $155\mathrm{GeV}<m_{{\tilde{\chi }}_1^0}<230\mathrm{}\mathrm{GeV}.$ These results are consistent with neutralino annihilation patterns that emerge from recent theoretical analysis on cosmic ray positron excess data reported by the HEAT Collaboration. The suggested methodology can be applied to test other annihilation channels of the neutralino, as well as other particle candidates for thermal weakly interacting massive particle gas relics.

By cooling of equilibrium lattice fields at finite temperature in $\mathrm{SU}\left(2\right)\mathrm{}$ gauge theory it has been shown that topological objects (calorons) observed on the lattice in the confined phase possess a dyonic substructure which becomes visible under certain circumstances. Here we show that with the increasing temporal lattice extent the distribution in the caloron parameter space is modified such that the calorons appear nondissociated into constituent dyons. Still the calorons have nontrivial holonomy which is demonstrated by the Polyakov line behavior for these configurations. At vanishing temperature (on a symmetric lattice) topological lumps obtained by cooling show rotational symmetry in 4D for the action density, but a characteristic internal double-peak structure of Polyakov lines with respect to all (temporal and spatial) directions.

We consider the spin polarization of leptons produced in neutrino and antineutrino nucleon deep inelastic scattering, via charged currents, and we study the positivity constraints on the spin components in a model independent way. These results are very important, in particular in the case of ${\tau }^{\pm }$ leptons, because the polarization information is crucial for all future neutrino oscillation experiments.

We investigate a model in which the Yukawa coupling form is constructed using two kinds of matrix ${(M}_0$ and $M_1).\mathrm{}$ For example, in the SO(10) grand unified theory model, $M_0$ and $M_1$ are Yukawa couplings generated by the 10 and 126 Higgs scalars. We study how this model can give the observed mass and mixings of quarks and leptons. Parameter fitting is fully scanned by assuming all the input data to be normally distributed around the center value.

We report measurements of the radiative decay $\overrightarrow{B}{K}^{*}\gamma .$ The analysis is based on a data sample containing $85.0\times {10}^6$ B meson pairs collected by the Belle detector at the KEKB storage ring. We measure branching fractions of $\mathcal{B}{(B}^0\to K^{*0}\gamma )=(4.01\mathrm{}\pm 0.21\pm 0.17)\times {10}^{-5}$ and $\mathcal{B}{(B}^{+}\to K^{*+}\gamma )=(4.25\mathrm{}\pm 0.31\pm 0.24)\times {10}^{-5},$ where the first and second errors are statistical and systematic, respectively. The isospin asymmetry between $B^0$ and $B^{+}$ decay widths is measured to be ${\Delta }_{0+}=+0.012\mathrm{}\pm 0.044\pm 0.026,$ assuming an equal production rate for $B^0{B}^0$ and $B^{+}{B}^{-}$ pairs from the ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}$ resonance. We search for a partial rate asymmetry between $\mathrm{CP}$ conjugate modes, and find $A_{\mathrm{CP}}\left(\overrightarrow{B}{K}^{*}\gamma \right)=-0.015\pm 0.044\pm \mathrm{0.012.}$

We explore the potential of the CERN Axion Solar Telescope (CAST) for testing the presence of large extra dimensions. The CAST experiment has originally been proposed to search for solar axions with a sensitivity supposed to provide a limit on the axion-photon coupling $g_{a\gamma \gamma }\lesssim 5\times {10}^{-11}{\mathrm{GeV}}^{-1\mathrm{}}$ or even lower. The expected bound on the coupling constant is by a factor of ten more stringent than the current experimental results. This bound extends for the first time beyond the limit dictated by astrophysical considerations. As a tuning experiment planning to explore the axion mass region up to about 1 eV, CAST would also be sensitive to the existence of Kaluza-Klein massive states. Therefore, the detection of x rays at least at two pressures may be the signature of large extra dimensions. From this requirement we find that CAST may test (two) large extra dimensions with a (common) compactification radius R down to around 250 nm if $m_{\mathrm{PQ}}<1/\left(2R\right),$ and down to around 370 nm if $1/\left(2R\right)<m_{\mathrm{PQ}},$ where $m_{\mathrm{PQ}}$ is the Peccei-Quinn mass.

Nonrelativistic charged particles and strings coupled with Abelian gauge fields are quantized in a geometric representation that generalizes the loop representation. We consider three models: the string in self-interaction through a Kalb-Ramond field in four dimensions, the topological interaction of two particles due to a BF term in $2+1$ dimensions, and the string-particle interaction mediated by a BF term in $3+1$ dimensions. In the first case one finds that a consistent “surface representation” can be built provided that the coupling constant is quantized. The geometrical setting that arises corresponds to a generalized picture of the lines of Faraday: quantum states are labeled by the shape of the string, from which emanate “Faraday’s surfaces.” In the other models, the topological interaction can also be described by geometrical means. It is shown that the open-path (or open-surface) dependence carried by the wave functional in these models can be eliminated through a unitary transformation, except by the remaining dependence on the boundary of the path (or surface). This feature is closely related to the presence of anomalous statistics in the $2+1$ model, and to a generalized “anyonic behavior” of the string in the other case.

We show how the use of the normal projection of the Einstein tensor as a set of boundary conditions relates to the propagation of the constraints, for two representations of the Einstein equations with vanishing shift vector: the Arnowitt-Deser-Misner formulation, which is ill posed, and the Einstein-Christoffel formulation, which is symmetric hyperbolic. Essentially, the components of the normal projection of the Einstein tensor that act as nontrivial boundary conditions are linear combinations of the evolution equations with the constraints that are not preserved at the boundary, in both cases. In the process, the relationship of the normal projection of the Einstein tensor to the recently introduced “constraint-preserving” boundary conditions becomes apparent.

Hawking’s argument for information loss in black hole evaporation rests on the assumption of independent Hilbert spaces for the interior and exterior of a black hole. We argue that such independence cannot be established without incorporating strong gravitational effects that undermine locality and invalidate the use of quantum field theory in a semiclassical background geometry. These considerations should also play a role in a deeper understanding of horizon complementarity.

We study the anisotropies of the galactic confusion noise background and its effects on LISA data analysis. LISA has two data streams of gravitational wave signals relevant for the low frequency regime. Because of the anisotropies of the background, the matrix for their confusion noises has off-diagonal components and depends strongly on the orientation of the detector plane. We find that the sky-averaged confusion noise level $\sqrt{S\left(f\right)\mathrm{}}$ could change by a factor of 2 in 3 months and would be minimum when the orbital position of LISA is around either the spring or autumn equinox.

We study the properties of the light pseudoscalar mesons in a three-flavor chiral quark model with nonlocal separable interactions. We concentrate on the evaluation of meson masses and decay constants, considering both the cases of Gaussian and Lorentzian nonlocal regulators. The results are found to be in quite good agreement with the empirical values, in particular in the case of the ratio $f_K{/f}_{\pi }$ and the anomalous decay ${\pi }^0\to \gamma \gamma .$ In addition, the model leads to a reasonable description of the observed phenomenology in the $\eta -{\eta }^{\prime }$ sector, even though it implies the existence of two significantly different state mixing angles.

It is shown that the addition of a nonlinear term to the Lagrangian of the electromagnetic field yields a fluid with an asymptotically super-negative equation of state, causing an accelerated expansion of the Universe. Some general properties of nonlinear electromagnetism in cosmology are also discussed.

We present the first examples of cosmological solutions to four-dimensional heterotic models which include an evolving bundle modulus. The particular bundle modulus we consider corresponds to the width of a gauge five brane. As such our solutions can be used to describe the evolution in one of these models after a small instanton transition. We find that certain properties are generic to these solutions, regardless of initial conditions. This enables us to make some definite statements about the dynamics subsequent to a small instanton transition despite the fact that we cannot microscopically describe the process itself. We also show that an effective description of the small instanton transition by a continuous matching of fields and their first derivatives is precluded by the form of the respective low-energy theories before and after the transition.

We compute for the first time very highly damped quasinormal modes of the (rotating) Kerr black hole. Our numerical technique is based on a decoupling of the radial and angular equations, performed using a large-frequency expansion for the angular separation constant ${}_s{A}_{\mathrm{lm}}.$ This allows us to go much further in overtone number than ever before. We find that the real part of the quasinormal frequencies approaches a nonzero constant value which does not depend on the spin s of the perturbing field or on the angular index l: ${\omega }_R=m\varpi \mathrm{}\left(a\right).$ We numerically compute $\varpi \mathrm{}\left(a\right).$ Leading-order corrections to the asymptotic frequency are likely to be $\sim 1/{\omega }_I.$ The imaginary part grows without bound, the spacing between consecutive modes being a monotonic function of a.

We consider stochastically quantized self-interacting scalar fields as suitable models to generate dark energy in the Universe. Second quantization effects lead to new and unexpected phenomena if the self-interaction strength is strong. The stochastically quantized dynamics can degenerate to a chaotic dynamics conjugated to a Bernoulli shift in fictitious time, and the right amount of vacuum energy density can be generated without fine-tuning. It is numerically observed that the scalar field dynamics distinguishes fundamental parameters such as the electroweak and strong coupling constants as corresponding to local minima in the dark energy landscape. Chaotic fields can offer possible solutions to the cosmological coincidence problem, as well as to the problem of uniqueness of vacua.

Theoretical considerations prompted by the discovery of the exotic ${\Theta }^{+}\left(uudd\overline{s}\right)$ led us to propose a dynamical picture emphasizing the role of diquark correlations, which are also useful in elucidating other aspects of low-energy QCD. A notable prediction of this picture is the existence of new exotic and nonexotic $S=-2$ “cascade” baryons with specific, characteristic properties. We argue here that recent observations by the NA49 Collaboration are broadly consistent with our predictions, and propose further tests.