Data samples corresponding to the isospin-violating decay $D_s^{*+}\to D_s^{+}{\pi }^0$ and the decays $D_s^{*+}\to D_s^{+}\gamma$, $D^{*0}\to D^0{\pi }^0$ and $D^{*0}\to D^0\gamma$ are reconstructed using $90.4$ ${\mathrm{fb}}^{-1}$ of data recorded by the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider. The following branching ratios are extracted: $\Gamma (D_s^{*+}\to D_s^{+}{\pi }^0)/\Gamma (D_s^{*+}\to D_s^{+}\gamma )=0.062\pm 0.005(\mathrm{stat}.)\pm 0.006(\mathrm{syst}.)$ and $\Gamma (D^{*0}\to D^0{\pi }^0)/\Gamma (D^{*0}\to D^0\gamma )=1.74\pm 0.02(\mathrm{stat}.)\pm 0.13(\mathrm{syst}.)$. Both measurements represent significant improvements over present world averages.

We reanalyze high-energy QCD scattering regimes from scattering in cutoff AdS space via gravity-gauge dualities (a la Polchinski-Strassler). We look at ’t Hooft scattering, Regge behavior, and black hole creation in AdS space. Black hole creation in the gravity dual is analyzed via gravitational shockwave collisions. We prove the saturation of the QCD Froissart unitarity bound, corresponding to the creation of black holes of AdS size, as suggested by Giddings.

We are developing a general, unified, and rigorous analytical framework for using gravitational lensing by compact objects to test different theories of gravity beyond the weak-deflection limit. In this paper we present the formalism for computing corrections to lensing observables for static, spherically symmetric gravity theories in which the corrections to the weak-deflection limit can be expanded as a Taylor series in one parameter, namely, the gravitational radius of the lens object. We take care to derive coordinate-independent expressions and compute quantities that are directly observable. We compute series expansions for the observables that are accurate to second order in the ratio $\epsilon ={\vartheta }_{•}/{\vartheta }_E$ of the angle subtended by the lens’s gravitational radius to the weak-deflection Einstein radius, which scales with mass as $\epsilon \propto M_{•}^{1/2}$. The positions, magnifications, and time delays of the individual images have corrections at both first and second order in $\epsilon$, as does the differential time delay between the two images. Interestingly, we find that the first-order corrections to the total magnification and centroid position vanish in all gravity theories that agree with general relativity in the weak-deflection limit, but they can remain nonzero in modified theories that disagree with general relativity in the weak-deflection limit. For the Reissner-Nordström metric and a related metric from heterotic string theory, our formalism reveals an intriguing connection between lensing observables and the condition for having a naked singularity, which could provide an observational method for testing the existence of such objects. We apply our formalism to the galactic black hole and predict that the corrections to the image positions are at the level of $10\mu \mathrm{arc}\mathrm{s}$ (microarcseconds), while the correction to the time delay is a few hundredths of a second. These corrections would be measurable today if a pulsar were found to be lensed by the galactic black hole, and they should be readily detectable with planned missions like MAXIM.

We study the gravitational field of a spinning radiation beam pulse (a gyraton) in a $D$-dimensional asymptotically AdS spacetime. It is shown that the Einstein equations for such a system reduce to a set of two linear equations in a $(D-2)$-dimensional space. By solving these equations we obtain a metric which is an exact solution of gravitational equations with the (negative) cosmological constant. The explicit metrics for $4D$ and $5D$ gyratons in asymptotically AdS spacetime are given and their properties are discussed.

We study static magnetic monopoles in the context of varying-$\alpha$ theories and show that there is a group of models for which the ’t Hooft-Polyakov solution is still valid. Nevertheless, in general static magnetic monopole solutions in varying-$\alpha$ theories depart from the classical ’t Hooft-Polyakov solution with the electromagnetic energy concentrated inside the core seeding spatial variations of the fine-structure constant. We show that Equivalence Principle constraints impose tight limits on the allowed variations of $\alpha$ induced by magnetic monopoles which confirms the difficulty to generate significant spatial variation of the fine-structure constant found in previous works. This is true even in the most favorable case where magnetic monopoles are the source for these variations.

The dark energy component of the Universe is often interpreted either in terms of a cosmological constant or as a scalar field. A generic feature of the scalar field models is that the equation of state parameter $w\equiv P/\rho$ for the dark energy need not satisfy $w=-1$ and, in general, it can be a function of time. Using the Markov chain Monte Carlo method we perform a critical analysis of the cosmological parameter space, allowing for a varying $w$. We use constraints on $w(z)$ from the observations of high redshift supernovae (SN), the Wilkinson Microwave Anisotropy Probe (WMAP) observations of cosmic microwave background (CMB) anisotropies, and abundance of rich clusters of galaxies. For models with a constant $w$, the $\Lambda \mathrm{CDM}$(cold dark matter) model is allowed with a probability of about 6% by the SN observations while it is allowed with a probability of 98.9% by WMAP observations. The $\Lambda \mathrm{CDM}$ model is allowed even within the context of models with variable $w$: WMAP observations allow it with a probability of 99.1% whereas SN data allows it with 23% probability. The SN data, on its own, favors phantom-like equation of state ($w<-1$) and high values for ${\Omega }_{\mathrm{NR}}$. It does not distinguish between constant $w$ (with $w<-1$) models and those with varying $w(z)$ in a statistically significant manner. The SN data allows a very wide range for variation of dark energy density, e.g., a variation by factor ten in the dark energy density between $z=0$ and $z=1$ is allowed at 95% confidence level. WMAP observations provide a better constraint and the corresponding allowed variation is less than a factor of 3. Allowing for variation in $w$ has an impact on the values for other cosmological parameters in that the allowed range often becomes larger. There is significant tension between SN and WMAP observations; the best fit model for one is often ruled out by the other at a very high confidence limit. Hence results based on only one of these can lead to unreliable conclusions. Given the divergence in models favored by individual observations, and the fact that the best fit models are ruled out in the combined analysis, there is a distinct possibility of the existence of systematic errors which are not understood.

The prospects for indirect detection of dark matter at the galactic center with $\gamma$-ray experiments like the space telescope GLAST, and air Cherenkov telescopes like HESS, CANGAROO, MAGIC and VERITAS depend sensitively on the mass profile within the inner parsec. We calculate the distribution of dark matter on subparsec scales by integrating the time-dependent Fokker-Planck equation, including the effects of self-annihilations, scattering of dark matter particles by stars, and capture in the supermassive black hole. We consider a variety of initial dark matter distributions, including models with very high densities (“spikes”) near the black hole, and models with “adiabatic compression” of the baryons. The annihilation signal after ${10}^{10}\mathrm{yr}$ is found to be substantially reduced from its initial value, but in dark matter models with an initial spike, order-of-magnitude enhancements can persist compared with the rate in spike-free models.

Purely baryonic dark matter dominated models like modified Newtonian dynamics (MOND) based on modification of Newtonian gravity have been successful in reproducing some dynamical properties of galaxies. More recently, a relativistic formulation of MOND proposed by Bekenstein seems to agree with cosmological large scale structure formation. In this work, we revise the agreement of MOND with observations in light of the new results on the cosmic microwave anisotropies provided by the $2003$ flight of Boomerang. The measurements of the height of the third acoustic peak, provided by several small scale CMB experiments have reached enough sensitivity to severely constrain models without cold dark matter. Assuming that acoustic peak structure in the CMB is unchanged and that local measurements of the Hubble constant can be applied, we find that the cold dark matter is strongly favored with Bayesian probability ratio of about one in two hundred.

The fact that muon neutrinos ${\nu }_{\mu }$ oscillating into the mixture of tau neutrinos ${\nu }_{\tau }$ and sterile neutrinos ${\nu }_s$ has been studied to explain the atmospheric ${\nu }_{\mu }$ disappearance. In this scenario, the effect of Earth matter is a key in determining the fraction of ${\nu }_s$. Considering that the Earth matter density has uncertainty and this uncertainty has significant effects in some neutrino oscillation cases, such as the $CP$ violation in very long baseline neutrino oscillations and the day-night asymmetry for solar neutrinos, we study the effects caused by this uncertainty in the above atmospheric ${\nu }_{\mu }$ oscillation scenario. We find that this uncertainty seems to have no significant effects and that the previous fitting results need not be modified.

A partial wave analysis of ${\chi }_{c0}\to {\pi }^{+}{\pi }^{-}{K}^{+}{K}^{-}$ in $\psi (2S)\to \gamma {\chi }_{c0}$ decay is presented using a sample of $14\times {10}^6$ $\psi (2S)$ events accumulated by the BES II detector. The data are fitted to the sum of relativistic covariant tensor amplitudes for intermediate resonant decay modes. From the fit, significant contributions to ${\chi }_{c0}$ decays from the channels $f_0(980)f_0(980)$, $f_0(980)f_0(2200)$, $f_0(1370)f_0(1710)$, $K^{*}(892{)}^0{\overline{K}}^{*}(892{)}^0$, $K_0^{*}(1430){\overline{K}}_0^{*}(1430)$, $K_0^{*}(1430){\overline{K}}_2^{*}(1430)+\mathrm{c}.\mathrm{c}.$, and $K_1(1270)K$ are found. Flavor-SU(3)-violating $K_1(1270)-K_1(1400)$ asymmetry is observed. Values obtained for the masses and widths of the resonances $f_0(1710)$, $f_0(2200)$, $f_0(1370)$, and $K_0^{*}(1430)$ are presented.

The possible existence of light sterile neutrinos is of great interest in many areas of particle physics, astrophysics, and cosmology. Furthermore, should the MiniBooNE experiment at Fermilab confirm the Liquid Scintillating Neutrino Detector (LSND) oscillation signal, then new measurements are required to identify the mechanism responsible for these oscillations. Possibilities include sterile neutrinos, $CP$ or $CPT$ violation, variable mass neutrinos, Lorentz violation, and extra dimensions. In this paper, we consider an experiment at a stopped pion neutrino source to determine if active-sterile neutrino oscillations with $\Delta m^2$ greater than $0.1{\mathrm{eV}}^2$ can account for the signal. By exploiting stopped ${\pi }^{+}$ decay to produce a monoenergetic ${\nu }_{\mu }$ source, and measuring the rate of the neutral current reaction ${\nu }_x{}^{12}\mathrm{C}\to {\nu }_x{}^{12}\mathrm{C}^{*}(15.11)$ as a function of distance from the source, we show that a convincing test for active-sterile neutrino oscillations can be performed.

We show how to do semiclassical nonperturbative computations within the worldline approach to quantum field theory using “worldline instantons.” These worldline instantons are classical solutions to the Euclidean worldline loop equations of motion, and are closed spacetime loops parametrized by the proper time. Specifically, we compute the imaginary part of the one-loop effective action in scalar QED using “worldline instantons” for a wide class of inhomogeneous electric field backgrounds. We treat both time-dependent and space-dependent electric fields and note that temporal inhomogeneities tend to shrink the instanton loops, while spatial inhomogeneities tend to expand them. This corresponds to temporal inhomogeneities tending to enhance local pair production, with spatial inhomogeneities tending to suppress local pair production. We also show how the worldline instanton technique extends to spinor QED.

The issue of domain walls in the recently extended Veneziano-Yankielowicz theory is investigated and we show that they have an interesting substructure. We also demonstrate the presence of a noncompact modulus. The associated family of degenerate solutions is physically due to the presence of a valley of vacua in the enlarged space of fields. This is a feature of the extended Veneziano-Yankielowicz theory. Unfortunately the above properties do not match the ones expected for the domain walls of $\mathcal{N}=1$ super Yang-Mills.

In this work we derive nonsingular BPS string solutions from an action that captures the essential features of a $D$-brane–anti-$D$-brane system compactified to four dimensions. The model we consider is a supersymmetric Abelian Higgs model with a $D$-term potential coupled to an axion-dilaton multiplet. The strings in question are axionic $D$-term strings which we identify with the $D$-strings of type II string theory. In this picture the Higgs field represents the open string tachyon of the $D-\overline{D}$ pair and the axion is dual to a Ramond-Ramond form. The crucial term allowing the existence of nonsingular BPS strings is the Fayet-Iliopoulos term, which is related to the tensions of the $D$-string and of the parent branes. Despite the presence of the axion, the strings are BPS and carry finite energy, due to the fact that the space gets very slowly decompactified away from the core, screening the long range axion field (or equivalently the theory approaches an infinitely weak $4D$ coupling). Within our $4D$ effective action we also identify another class of BPS string solutions ($s$-strings) which have no ten-dimensional analog, and can only exist after compactification.

In this paper we review a model based on loop quantum cosmology that arises from a symmetry reduction of the self-dual Plebanski action. In this formulation the symmetry reduction leads to a very simple Hamiltonian constraint that can be quantized explicitly in the framework of loop quantum cosmology. We investigate the phenomenological implications of this model in the semiclassical regime and compare those with the known results of the standard Loop Quantum Cosmology.

We consider a deformation of five-dimensional warped gravity with bulk and boundary mass terms to quadratic order in the action. We show that massless zero modes occur for special choices of the masses. The tensor zero mode is a smooth deformation of the Randall-Sundrum graviton wave function and can be localized anywhere in the bulk. There is also a vector zero mode with similar localization properties, which is decoupled from conserved sources at tree level. Interestingly, there are no scalar modes, and the model is ghost-free at the linearized level. When the tensor zero mode is localized near the IR brane, the dual interpretation is a composite graviton describing an emergent (induced) theory of gravity at the IR scale. In this case Newton’s law of gravity changes to a new power law below the millimeter scale, with an exponent that can even be irrational.

There exist a number of models in the literature in which the weak interactions are derived from a chiral gauge theory based on a larger group than $SU(2{)}_L\times U(1{)}_Y$. Such theories can be constructed so as to be anomaly free and consistent with precision electroweak measurements, and may be interpreted as a deconstruction of an extra dimension. They also provide interesting insights into the issues of flavor and dynamical electroweak symmetry breaking, and can help to raise the mass of the Higgs boson in supersymmetric theories. In this work we show that these theories can also give rise to baryon and lepton number violating processes, such as nucleon decay and spectacular multijet events at colliders, via the instanton transitions associated with the extended gauge group. For a particular model based on $SU(2{)}_1\times SU(2{)}_2$, we find that the $B+L$ violating scattering cross sections are too small to be observed at the LHC, but that the lower limit on the lifetime of the proton implies an upper bound on the gauge couplings.

The most general Higgs potential of the two-Higgs-doublet model (2HDM) contains three squared-mass parameters and seven quartic self-coupling parameters. Among these, one squared-mass parameter and three quartic coupling parameters are potentially complex. The Higgs potential explicitly violates $CP$ symmetry if and only if no choice of basis exists in the two-dimensional Higgs flavor space in which all the Higgs potential parameters are real. We exhibit four independent potentially complex invariant (basis-independent) combinations of mass and coupling parameters and show that the reality of all four invariants provides the necessary and sufficient conditions for an explicitly $CP$-conserving 2HDM scalar potential. Additional potentially complex invariants can be constructed that depend on the Higgs field vacuum expectation values (vevs). We demonstrate how these can be used together with the vev-independent invariants to distinguish between explicit and spontaneous $CP$ violation in the Higgs sector.

Proton stability seems to constrain rather strongly any baryon number violating process. We investigate the possibility of baryon number violating processes involving right-handed dynamics or higher generation quarks. Our results strongly suggest that there will be no possibility to observe baryon number violation in $\tau$ or higher generation quark decays, at any future machine.