We study the evolution of perturbations on a moving probe D3-brane coupled to a four-form field in an ${\mathrm{AdS}}_5$-Schwarzschild bulk. The unperturbed dynamics are parametrized by a conserved energy E and lead to a Friedmann-Robertson-Walker (FRW) “mirage” cosmology on the brane with a scale factor $a\left(\tau \right).\mathrm{}$ The fluctuations about the unperturbed worldsheet are then described by a scalar field $\phi (\tau ,\overrightarrow{x}).\mathrm{}$ We derive an equation of motion for $\phi ,$ and find that in certain regimes of a the effective mass squared is negative. On an expanding Bogomol’nyi-Prasad-Sommerfield (BPS) brane with $E=0\mathrm{}$ superhorizon modes grow as $a^4$ while subhorizon modes are stable. When the brane contracts, all modes grow. We also briefly discuss the case when $E>\mathrm{}0,$ BPS antibranes as well as non-BPS branes. Finally, the perturbed brane embedding gives rise to scalar perturbations in the FRW universe. We show that $\phi$ is proportional to the gauge invariant Bardeen potentials on the brane.

We construct a simple nonsingular cosmological model in which the currently observed expansion phase was preceded by a contraction. This is achieved, in the framework of pure general relativity, by means of a radiation fluid and a free scalar field having negative energy. We calculate the power spectrum of the scalar perturbations that are produced in such a bouncing model under the assumption of initial vacuum state for the quantum field associated with the hydrodynamical perturbation. The matching conditions applying to this bouncing model are derived and shown to be different from those in the case of a sharp transition. We show that if our bounce transition is smoothly connected to a slowly contracting phase, this provides a new way to generate a scale invariant power spectrum.

The double $J/\psi$ production in $p\overline{p}$ collisions is reexamined. It is found that the $J/\psi$ pair production rate obtained in the color-singlet model, at leading order in ${\alpha }_s$ and with transverse momentum $p_T>4\mathrm{}\mathrm{GeV},$ is similar in magnitude to what is derived from the color-octet mechanism. Although the double $J/\psi$ production process was proven to be observable with data yet collected at the Fermilab Tevatron detectors, our findings show that the analysis on this process using the accumulated data would be no help in the aim of clarifying the quarkonium production mechanisms, but can give information on the nature of the color-singlet prescription for charmonium production. Nevertheless, with more data to be collected in the future, the evidently different features of $J/\psi$ pair production in $p_T$ distribution in two different schemes enable experimental study to give a decisive conclusion on them.

The transverse lepton polarization asymmetry in ${\pi }_{l2\mathrm{}\gamma }$ decays may probe T-violating interactions beyond the Standard Model. Dalitz plot distributions of the expected effects are presented and compared to the contribution from the Standard Model final-state interactions. We give an example of a phenomenologically viable model, where a considerable contribution to the transverse lepton polarization asymmetry arises.

We discuss all contributions from Zweig-rule-satisfying SU(3)-symmetric inelastic final state interaction (FSI)-induced corrections in B decays to $\pi \pi ,$ $\pi K,$ $K\overline{K},$ $\pi \eta \left({\eta }^{\prime }\right),$ and $K\eta \left({\eta }^{\prime }\right).\mathrm{}$ We show how all of these FSI corrections lead to a simple redefinition of the amplitudes, permitting the use of a simple diagram-based description, in which, however, weak phases may enter in a modified way. The inclusion of FSI corrections admitted by the present data allows an arbitrary relative phase between the penguin and tree short-distance amplitudes. The FSI-induced error of the method, in which the value of the weak phase $\gamma$ is to be determined by combining future results from $B^{+}{,B}_d^0{,B}_s^0$ decays to $K\pi ,$ is estimated to be of the order of $5°$ for $\gamma \approx 50°-60°.$

Inspired by recent developments in particle physics, the so-called brane world cosmology seems to provide an alternative explanation for the present dark energy problem. In this paper we use the estimated age of high-$z$ objects to constrain the value of the cosmological parameters in some particular scenarios based on this large scale modification of gravity. We show that such models are compatible with these observations for values of the crossover distance between the 4 and 5 dimensions of the order of $r_c<~{1.67H}_o^{-1}.$

In the context of gauge-gravity duality, we try to understand better the proposed duality between the fractional D2-brane supergravity solutions of Cvetič, Gibbons, Lü, and Pope [Nucl. Phys. $\mathbf{B}606\mathrm{},$ 18 (2001)] and a confining $\mathrm{}(2+1)\mathrm{}$-dimensional gauge theory. Based on the similarities between this fractional D2-brane solution and D3-brane supergravity solutions with more firmly established gauge theory duals, we conjecture that a confining q string in the $\mathrm{}(2+1)\mathrm{}$-dimensional gauge theory is dual to a wrapped D4-brane. In particular, the D4-brane looks like a string in the gauge theory directions but wraps an ${\mathbf{S}}^3\subset {\mathbf{S}}^4$ in the transverse geometry. For one of the supergravity solutions, we find a near quadratic scaling law for the tension: $T\sim q\left(N-q\right).\mathrm{}$ Based on the tension, we conjecture that the gauge theory dual is $\mathrm{SU}\left(N\right)\mathrm{}$ far in the infrared. We also conjecture that a quadratic or near quadratic scaling is a generic feature of confining $\mathrm{}(2+1)\mathrm{}$-dimensional $\mathrm{SU}\left(N\right)\mathrm{}$ gauge theories.

We have reanalyzed constraints on the equation of state parameter, $w_Q\equiv P/\rho ,$ of the dark energy, using several cosmological data sets and relaxing the usual constraint $w_Q>~-1.$ We find that combining cosmic microwave background, large scale structure, and type Ia supernova data yields a nontrivial lower bound on $w_Q.$ At 95.4% confidence we find, assuming a flat geometry of the universe, a bound of $-2.68<\mathrm{}{w}_Q<-0.78$ if $w_Q$ is taken to be a completely free parameter. Reassuringly we also find that the constraint $w_Q>~-1$ does not significantly bias the overall allowed region for $w_Q.$ When this constraint is imposed the 95.4% confidence bound is $-1<~w_Q<-\mathrm{0.71.}$ Also, a pure cosmological constant $(w=-1)$ is an excellent fit to all available data. Based on simulations of future data from the Planck CMB experiment and the SNAP and SNfactory supernova experiments we estimate that it will be possible to constrain $w_Q$ at the 5% level in the future.

The possible effects of noncommutative geometry on weak $\mathrm{CP}$ violation and unitarity triangles are discussed by taking into account a simple version of the momentum-dependent quark mixing matrix in the noncommutative standard model. In particular, we calculate nine rephasing invariants of $\mathrm{CP}$ violation and illustrate the noncommutative $\mathrm{CP}$-violating effect in a couple of charged D-meson decays. We also show how inner angles of the deformed unitarity triangles are related to $\mathrm{CP}$-violating asymmetries in some typical $B_d$ and $B_s$ transitions into $\mathrm{CP}$ eigenstates. B-meson factories are expected to help probe or constrain noncommutative geometry at low energies in the near future.

We extend chiral perturbation theory to include linear dependence on the lattice spacing a for the Wilson action. The perturbation theory is written as a double expansion in the small quark mass $m_q$ and lattice spacing a. We present formulas for the mass and decay constant of a flavor-nonsinglet meson in this scheme to order a and $m_q^2.$ The extension to the partially quenched theory is also described.

We investigate de Sitter/conformal field theory (dS/CFT) correspondence in two dimensions. We define the conserved mass of de Sitter spacetime and formulate the correspondence along the lines of the anti–de Sitter/conformal field theory duality. The asymptotic symmetry group, mass, and central charge of de Sitter spacetime are equal to those of anti–de Sitter spacetime. The entropy of two-dimensional de Sitter spacetime is evaluated by applying the Cardy formula. We calculate the boundary correlators induced by the propagation of the dilaton in two-dimensional de Sitter space. Although the dilaton is a tachyonic perturbation in the bulk, boundary conformal correlators have a positive dimension.

We suggest a new method for the calculation of the nonlocal part of the effective action. It is based on the resummation of the perturbation series for the heat kernel and its functional trace at large values of the proper time parameter. We derive a new, essentially nonperturbative, nonlocal contribution to the effective action in spacetimes with dimensions $d>\mathrm{}2.\mathrm{}$

We compute the overlap function between post-Newtonian (PN) templates and gravitational signals emitted by binary systems composed of one neutron star and one point mass, obtained by a perturbative approach. The calculations are performed for different stellar models and for different detectors, to estimate how effectual and faithful the PN templates are, and to establish whether effects related to the internal structure of neutron stars may possibly be extracted by the matched filtering technique.

A family of wormhole instanton solutions is obtained in the non-Abelian Born-Infeld theory in the presence of a positive cosmological constant. These wormholes have a closed Friedmann-Robertson-Walker geometry and a nontrivial SO(4)-symmetric gauge sector. It is found that when the matter sector in the action is dominated by Born-Infeld terms inducing a string gas behavior, then no wormhole solutions are admissible. However, when the gauge fields asymptotically lead to a radiation scenario, wormhole solutions become possible. The presence of Born-Infeld perturbations in this stage determines specific modifications for the wormhole dynamics. Some of these physical implications are consequently discussed. In particular, we comment on how they can modify the quantization in energy levels of the wormhole solution. We also mention how this may affect the quantization of topological charges and conservation of fermion number.

We compute primordial light-element abundances for cases with a fine structure constant $\alpha$ different from the present value, including many sources of $\alpha$ dependence neglected in previous calculations. Specifically, we consider contributions arising from Coulomb barrier penetration, photon coupling to nuclear currents, and the electromagnetic components of nuclear masses. We find the primordial abundances to depend more weakly on $\alpha$ than previously estimated, by up to a factor of 2 in the case of ${}^7\mathrm{Li}.$ We discuss the constraints on variations in $\alpha$ from the individual abundance measurements and the uncertainties affecting these constraints. While the present best measurements of primordial D/H, ${}^4\mathrm{He}/\mathrm{H},$ and ${}^7\mathrm{Li}/\mathrm{H}$ may be reconciled pairwise by adjusting $\alpha$ and the universal baryon density, no value of $\alpha$ allows all three to be accommodated simultaneously without consideration of systematic error. The combination of measured abundances with observations of acoustic peaks in the cosmic microwave background favors no change in $\alpha$ within the uncertainties.

We present a new, model-independent approach for measuring non-Gaussianity of the cosmic microwave background (CMB) anisotropy pattern. Our approach is based on the empirical distribution function of the normalized spherical harmonic expansion coefficients $a_{\mathcal{l}m}$ of a nearly full-sky CMB map, like the ones expected from forthcoming satellite experiments. Using a set of Kolmogorov-Smirnov type tests, we check for Gaussianity and independency of the $a_{\mathcal{l}m}.$ We test the method on two non-Gaussian toy models of the CMB, one generated in spherical harmonic space and one in pixel (real) space. We also provide some rigorous results, possibly of independent interest, on the exact distribution of the spherical harmonic coefficients normalized by an estimated angular power spectrum.

A recently proposed scheme is used to saturate the spectral side of the QCD sum rules derived from the thermal, two-point correlation functions of the vector and the axial-vector currents. At low temperature, it constructs the spectral representation from all the one-loop Feynman diagrams for the two-point functions. The old saturation scheme treats incorrectly some of these contributions. We end up with the familiar QCD sum rules obtained from the difference of the two corresponding vacuum correlation functions. The possibility of obtaining new sum rules in other media is discussed.

Infrared properties of the triangle anomaly and the “anomaly pole” are elaborated and applied to the study of high-energy scattering in QCD, when the gauge symmetry is partially broken to SU(2). It is shown that the chiral flavor anomaly provides a wee-gluon component for Goldstone bosons that combines with interactions due to the U(1) anomaly to produce an infrared transverse momentum scaling divergence in scattering amplitudes. After the divergence is factorized out, as a wee-gluon condensate in the infinite momentum pion, the remaining physical amplitudes have confinement and chiral symmetry breaking. A lowest-order contribution to the pion scattering amplitude is calculated in detail. Although originating from very complicated diagrams, the amplitude has a remarkable (semi)perturbative simplicity. The momentum structure is that of single gluon exchange but zero transverse momentum quarks inject additional spin and color structure via anomaly interactions.

We define a minimal model with universal extra dimensions, and begin to study its phenomenology. The collider signals of the first Kaluza-Klein (KK) level are surprisingly similar to those of a supersymmetric model with a nearly degenerate superpartner spectrum. The lightest KK particle (LKP) is neutral and stable because of KK parity. KK excitations cascade decay to the LKP yielding missing energy signatures with relatively soft jets and leptons. Level 2 KK modes may also be probed via their KK number violating decays to standard model particles. In either case we provide initial estimates for the discovery potential of the Fermilab Tevatron and the CERN Large Hadron Collider.