In this note, we investigate the homogeneous radial dynamics of (Dp, NS5) systems without and with one compactified transverse direction, in the framework of Dirac-Born-Infeld effective action. During the homogeneous evolution, the electric field on the D-brane is always conserved and the radial motion could be reduced to a one-dimension dynamical system with an effective potential. When the Dp-brane energy is not high, the brane moves in a restricted region, with the orbits depending on the conserved energy, angular momentum through the form of the effective potential. When the Dp-brane energy is high enough, it can escape to infinity. It turns out that the conserved angular momentum plays an interesting role in the dynamics. Moreover, we discuss the gauge dynamics around the tachyon vacuum and find that the dynamics is very reminiscent of the string fluid in the rolling tachyon case.

We construct models of rotating stars using the perturbative approach introduced by J. Hartle in 1967, and a set of equations of state proposed to model hadronic interactions in the inner core of neutron stars. We integrate the equations of stellar structure to third order in the angular velocity and show, comparing our results to those obtained with fully nonlinear codes, to what extent third order corrections are needed to accurately reproduce the moment of inertia of a star which rotates at rates comparable to that of the fastest isolated pulsars.

We study the possibility that dark matter is a baryon of a new strongly interacting gauge theory, which was introduced in the low energy theory of Cosmological SUSY Breaking (CSB). This particle can fit the observed dark matter density if an appropriate cosmological asymmetry is generated. The same mechanism can also explain the dark/baryonic matter ratio in the universe. The mass of the dark matter particle is in the multiple TeV range, and could be as high as 20 TeV.

The cosmic expansion history tests the dynamics of the global evolution of the universe and its energy density contents, while the cosmic growth history tests the evolution of the inhomogeneous part of the energy density. Precision comparison of the two histories can distinguish the nature of the physics responsible for the accelerating cosmic expansion: an additional smooth component—dark energy—or a modification of the gravitational field equations. With the aid of a new fitting formula for linear perturbation growth accurate to 0.05%–0.2%, we separate out the growth dependence on the expansion history and introduce a new growth index parameter $\gamma$ that quantifies the gravitational modification.

In the spacetime of n-dimensional static charged black hole we examine the mechanism by which the self-interacting scalar hair decay. It is turned out that the intermediate asymptotic behavior of the self-interacting scalar field is determined by an oscillatory inverse power law. We confirm our results by numerical calculations.

Nonperturbative studies of quantum gravity have recently suggested the possibility that the strength of gravitational interactions might slowly increase with distance. Here a set of generally covariant effective field equations are proposed, which are intended to incorporate the gravitational, vacuum-polarization induced, running of Newton’s constant $G$. One attractive feature of this approach is that, from an underlying quantum gravity perspective, the resulting long-distance (or large time) effective gravitational action inherits only one adjustable parameter $\xi$, having the units of a length, arising from dimensional transmutation in the gravitational sector. Assuming the above scenario to be correct, some simple predictions for the long-distance corrections to the classical standard model Robertson-Walker metric are worked out in detail, with the results formulated as much as possible in a model-independent framework. It is found that the theory, even in the limit of vanishing renormalized cosmological constant, generally predicts an accelerated power-law expansion at later times $t\sim \xi \sim 1/H$.

I construct initial data for equal-mass irrotational binary black holes using the conformal thin-sandwich puncture approach. I locate quasicircular orbits using the effective-potential method, and estimate the location of the innermost stable circular orbit (ISCO). The ISCO prediction is consistent with results for conformal thin-sandwich data produced using excision techniques. These results also show that the ISCOs predicted by the effective-potential and ADM-Komar mass-comparison methods agree for conformal thin-sandwich data, just as they did for Bowen-York data.

In the continuation of a preceding work, we derive a new expression for the metric in the near zone of an isolated matter system in post-Newtonian approximations of general relativity. The post-Newtonian metric, a solution of the field equations in harmonic coordinates, is formally valid up to any order, and is cast in the form of a particular solution of the wave equation, plus a specific homogeneous solution which ensures the asymptotic matching to the multipolar expansion of the gravitational field in the exterior of the system. The new form is suitable for practical computations of the gravitational radiation reaction forces in harmonic coordinates. It also provides some insights on the structure of the post-Newtonian expansion in general relativity and the radiation reaction terms therein.

Recently several models of traversable wormholes have been proposed which require only arbitrarily small amounts of negative energy to hold them open against self-collapse. If the exotic matter is assumed to be provided by quantum fields, then quantum inequalities can be used to place constraints on the negative energy densities required. In this paper, we introduce an alternative method for obtaining constraints on wormhole geometries, using a recently derived quantum inequality bound on the null-contracted stress-energy averaged over a timelike worldline. The bound allows us to perform a simplified analysis of general wormhole models, not just those with small quantities of exotic matter. We then use it to study, in particular, the models of Visser, Kar, and Dadhich (VKD) and the models of Kuhfittig. The VKD models are constrained to be either submicroscopic or to have a large discrepancy between throat size and curvature radius. A recent model of Kuhfittig is shown to be nontraversable. This is due to the fact that the throat of his wormhole flares outward so slowly that light rays and particles, starting from outside the throat, require an infinite lapse of affine parameter to reach the throat.

Based on the dynamical equivalence between higher order gravity and scalar-tensor gravity the parametrized post-Newtonian (PPN) limit of fourth order gravity is discussed. We exploit this analogy developing a fourth order gravity version of the Eddington PPN parameters. As a result, Solar System experiments can be reconciled with higher order gravity, if physical constraints descending from experiments are fulfilled.

We investigate the case of a homogeneous tachyon field coupled to gravity in a spatially flat Friedmann-Robertson-Walker spacetime. Assuming the field evolution to be exponentially decaying with time we solve the field equations and show that, under certain conditions, the scale factor represents an accelerating universe, following a phase of decelerated expansion. We make use of a model of dark energy (with $p=-\rho$) and dark matter ($p=0$) where a single scalar field (tachyon) governs the dynamics of both the dark components. We show that this model fits the current supernova data as well as the canonical $\Lambda \mathrm{CDM}$ model. We give the bounds on the parameters allowed by the current data.

We explore the properties of dark-energy models for which the equation of state, $w$, defined as the ratio of pressure to energy density, crosses the cosmological-constant boundary $w=-1$. We adopt an empirical approach, treating the dark energy as an uncoupled fluid or a generalized scalar field. We describe the requirements for a viable model, in terms of the equation of state and sound speed. A generalized scalar field cannot safely traverse $w=-1$, although a pair of scalars with $w>-1$ and $w<-1$ will work. A fluid description with a well-defined sound speed can also cross the boundary. Contrary to expectations, such a crossing model does not instantaneously resemble a cosmological constant at the moment $w=-1$ since the density and pressure perturbations do not necessarily vanish. But because a dark energy with $w<-1$ dominates only at very late times, and because the dark energy is not generally prone to gravitational clustering, then crossing the cosmological-constant boundary leaves no distinct imprint.

Nonlinear gravitational effects of large-scale local inhomogeneities on cosmic microwave background (CMB) anisotropies are studied, based on the relativistic second-order theory of perturbations in nonzero-$\Lambda$ flat cosmological models, which has been analytically derived by the present author, and on the second-order formula of CMB anisotropies derived by Mollerach and Matarrese. In this paper we derive the components of the CMB anisotropy power spectra in the range of $l=1\mathrm{\text{−}}22$ which are caused by asymmetric local inhomogeneities on scales of 300 Mpc. Using our results it is found that there is a possibility to explain the small north-south asymmetry of CMB anisotropies which has recently been observed.

The effective potential for radiatively broken electroweak symmetry in the single-Higgs-doublet standard model is explored to four sequentially subleading logarithm-summation levels (5-loops) in the dominant Higgs self-interaction couplant $\lambda$. We augment these results with all contributing leading logarithms in the remaining large but subdominant standard model couplants [$t$-quark, QCD and $SU(2)\otimes U(1)$ gauge couplants] as well as next to leading-logarithm contributions from the largest of these, the $t$-quark and QCD couplants. Order-by-order stability is demonstrated for earlier leading-logarithm predictions of an $\mathcal{O}$ (220 GeV) Higgs boson mass in conjunction with fivefold enhancement of the value for $\lambda$ over that anticipated from conventional spontaneous symmetry breaking.

We study $T$ violation in the three-body charmless baryonic decay of ${\overline{B}}^0\to \Lambda \overline{p}{\pi }^{+}$ through the $T$-odd triple product correlation in the standard model. We discuss the difference between $T$ violating triple product correlation and direct $CP$ violating rate asymmetries by showing the explicit strong and weak phase dependences. We find that the $T$ violating asymmetry is $10\%$, which is accessible to the current B factories at KEK and SLAC, while the $CP$ violating one $1.1\%$. We emphasize that this triple product correlation would be the first measurable direct $T$ violating effect predicted in the standard model, which provides a reliable test of the Cabbibo-Kobayashi-Maskawa mechanism of T violation.

We reconsider little-Higgs corrections to precision data. In five models with global symmetries SU(5), SU(6), SO(9) corrections are (although not explicitly) of “universal“ type. We get simple expressions for the $\widehat{S},\widehat{T},W,Y$ parameters, which summarize all effects. In all models $W,Y\ge 0$ and in almost all models $\widehat{S}>(W+Y)/2$. Results differ from previous analyses, which are sometimes incomplete, sometimes incorrect, and because we add LEP2 $e\overline{e}\to f\overline{f}$ cross sections to the data set. Depending on the model, the constraint on $f$ ranges between 2 and 20 TeV. We next study the simplest little-Higgs model (and propose a related model) which is not universal and affects precision data due to the presence of an extra $Z^{\prime }$ vector. By restricting the data set to the most accurate leptonic data we show how corrections to precision data generated by a generic $Z^{\prime }$ can be encoded in four effective $\widehat{S},\widehat{T},W,Y$ parameters, giving their expressions.

We analyze approaches to the partial or complete unification of gauge symmetries in theories with dynamical symmetry breaking. Several types of models are considered, including those that (i) involve sufficient unification to quantize electric charge, (ii) attempt to unify the three standard-model gauge interactions in a simple Lie group that forms a direct product with an extended technicolor group, and, most ambitiously, (iii) attempt to unify the standard-model gauge interactions with (extended) technicolor in a simple Lie group.

Using limits of large energy effective theory and heavy quark effective theory, we propose a simple parametrization of the heavy to light $H\to V$ semileptonic form factors. Then we reconsider $D\to V\ell {\nu }_{\ell }$ decays within a model which combines heavy meson and chiral symmetry. In our Lagrangians we include contributions coming from excited charm meson states, some of them recently observed. Within this framework we determine all parameters describing the shapes of the form factors and calculate branching ratios and helicity ratios for all $D\to V\ell {\nu }_{\ell }$ decays.

The merging procedure of tree-level matrix elements with the subsequent parton shower as implemented in SHERPA will be studied for the example of $W$ boson pair production at the Fermilab Tevatron. Comparisons with fixed order calculations at leading and next-to-leading order in the strong coupling constant and with other Monte Carlo simulations validate once more the impact and the quality of the merging algorithm and its implementation.