We consider a self-interacting scalar field whose mass saturates the Breitenlohner-Freedman bound, minimally coupled to Einstein gravity with a negative cosmological constant in $D>~3$ dimensions. It is shown that the asymptotic behavior of the metric has a slower fall-off than that of pure gravity with a localized distribution of matter, due to the back-reaction of the scalar field, which has a logarithmic branch decreasing as $r^{-\left(D-1\right)/2}\ln r$ for large radius r. We find the asymptotic conditions on the fields which are invariant under the same symmetry group as pure gravity with negative cosmological constant (conformal group in $D-1$ dimensions). The generators of the asymptotic symmetries are finite even when the logarithmic branch is considered but acquire, however, a contribution from the scalar field.

A code to evolve boson stars in 3D is presented as the starting point for the evolution of scalar field systems with arbitrary symmetries. It was possible to reproduce the known results related to perturbations discovered with 1D numerical codes in the past, which include evolution of stable and unstable equilibrium configurations. In addition, the apparent and event horizons masses of a collapsing boson star are shown for the first time. The present code is expected to be useful at evolving possible sources of gravitational waves related to scalar field objects and to handle toy models of systems perturbed with scalar fields in 3D.

We study the properties of cosmological density perturbations in a multi-component system consisting of a scalar field and a perfect fluid. We discuss the number of degrees of freedom completely describing the system, introduce a full set of dynamical gauge-invariant equations in terms of the curvature and entropy perturbations, and display an efficient formulation of these equations as a first-order system linked by a fairly sparse matrix. Our formalism includes spatial gradients, extending previous formulations restricted to the large-scale limit, and fully accounts for the evolution of an isocurvature mode intrinsic to the scalar field. We then address the issue of the adiabatic condition, in particular demonstrating its preservation on large scales. Finally, we apply our formalism to the quintessence scenario and clearly underline the importance of initial conditions when considering late-time perturbations. In particular, we show that entropy perturbations can still be present when the quintessence field energy density becomes non-negligible.

We study the expansion history of the universe up to a redshift of $\mathrm{z}=1.75\mathrm{}$ using the 194 recently published SnIa data by Tonry et al. and Barris et al. In particular we find the best fit forms of several cosmological models and $H\left(z\right)\mathrm{}$ ansatze, determine the best fit values of their parameters and rank them according to increasing value of ${\chi }_{\min }^2$ [the minimum value of ${\chi }^2$ for each $H\left(z\right)\mathrm{}$ ansatz]. We treat ${\Omega }_{0m}$ as a parameter using a reasonable prior and assume flat geometry of the universe. No prior assumptions are made about validity of energy conditions. The fitted models are fourteen and include standard cold dark matter (SCDM), cold dark matter with cosmological constant Λ (LCDM), dark energy with constant equation of state parameter w (quiessence), third order polynomial for $H(1+z),$ Chaplygin gas, Cardassian model, ${w\left(z\right)=w}_0{+w}_{1}z,$ ${w\left(z\right)=w}_0{+zw}_1/(1+z),$ an oscillating ansatz for $H\left(z\right),$ etc. All these models with the exception of SCDM are consistent with the present data. However, the quality of the fit differs significantly among them and so do the predicted forms of $w\left(z\right)\mathrm{}$ and $H\left(z\right)\mathrm{}$ at best fit. The worst fit among the data-consistent models considered corresponds to the simplest model LCDM $({\chi }_{\min }^2=198.7\mathrm{}$ for ${\Omega }_{0m}=0.34)$ while the best fit is achieved by the three parameter oscillating ansatz $({\chi }_{\min }^2=193.8).\mathrm{}$ Most of the best fit ansatze have an equation of state parameter $w\left(z\right)\mathrm{}$ that varies between $w\left(z\right)\mathrm{}\simeq -1$ for $z<\mathrm{}0.5\mathrm{}$ to $w\left(z\right)>0\mathrm{}$ for $z>\mathrm{}1.\mathrm{}$ This implies that the sign of the pressure of the dark energy may be alternating as the redshift increases. The goodness of fit of the oscillating $H\left(z\right)\mathrm{}$ ansatz lends further support to this possibility.

In loop quantum gravity, modifications to the geometrical density cause a self-interacting scalar field to accelerate away from a minimum of its potential. In principle, this mechanism can generate the conditions that subsequently lead to slow-roll inflation. The consequences for this mechanism of various quantization ambiguities arising within loop quantum cosmology are considered. For the case of a quadratic potential, it is found that some quantization procedures are more likely to generate a phase of slow-roll inflation. In general, however, loop quantum cosmology is robust to ambiguities in the quantization and extends the range of initial conditions for inflation.

We reanalyze the neutrino events from SN1987A in IMB and Kamiokande-II (KII) detectors, and compare them with the expectations from simple theoretical models of the neutrino emission. In both detectors the angular distributions are peaked in the forward direction, and the average cosines are 2 sigma above the expected values. Furthermore, the average energy in KII is low if compared with the expectations; but, as we show, the assumption that a few (probably one) events at KII have been caused by elastic scattering is not in contrast with the “standard” picture of the collapse and yields more satisfactory distributions in angle and (marginally) in energy. The observations give useful information on the astrophysical parameters of the collapse. We find that the mean energy of electron antineutrinos is $〈E〉=12\mathrm{}–15\mathrm{MeV},$ the total energy radiated around $(2\mathrm{}–5)\times {10}^{53}\mathrm{erg},$ and there is a hint for a relatively large radiation of nonelectronic neutrino species. These properties of the neutrino burst are not in disagreement with those suggested by the current theoretical paradigm, but the data leave wide space to nonstandard pictures, especially when neutrino oscillations are included.

The dynamics of a minimally coupled scalar field in the expanding universe is discussed with special reference to phantom cosmology. The evolution of the universe with a phantom field vis-à-vis a quintessence field is compared. Phantom cosmologies are found to have two special features: (i) occurrence of a singularity where the scale factor, the energy density, and Ricci curvature scalar diverge to infinity (this singularity occurs at a finite time, depending on the value of w during cosmic evolution), and (ii) degeneracy in the determination of ${w(z}_m)$ for a given transition redshift $z_m$ which seems to impart similar observational properties to corresponding phantom and quintessence models and makes both of them compatible with the cosmological observations. Although due to the uncertainties in the measurement of the Hubble constant $H_0,$ the Hubble dependent observational parameters yield only loose constraints over the range of w, the duality in the determination of w with respect to transition redshift may be used to constrain w. An observational test, based upon the observations of low redshift galactic clusters, is suggested to discriminate between the quintessence and phantom dark energy.

We study the corrections to the determination of $\sin \left(2\mathrm{}\beta \right)$ from the time dependent CP asymmetry of $B^0\to J/\Psi K_S$ which arise in the standard model. Although a precise prediction of these corrections is not possible we find that they are indeed extremely small, of the order of less than a per mil of the observed value. This means in turn that any deviation visible at the B factories will be a clear signal for new physics.

Strong mixing between right-handed strange and beauty squarks is a possible solution to the CP violation discrepancy in $\overrightarrow{B}\phi K_S$ decay as recently suggested by the Belle data. In this scenario, thanks to the strong mixing one of the strange-beauty squarks can be as light as 200 GeV, even though the generic supersymmetry scale is at TeV. In this work, we study the production of this light right-handed strange-beauty squark at hadronic colliders and discuss the detection in various decay scenarios. Detection prospect at the Tevatron run II is good for the strange-beauty squark mass up to about 300 GeV.

We calculate the decay distributions for inclusive $\overrightarrow{B}{X}_s\gamma$ and $\overrightarrow{B}{X}_u\mathcal{l}\overline{\nu }$ decays in the endpoint region, where radiative corrections are large. The computation is done using effective field theory methods. The matching coefficients are computed to $\mathcal{O}\left({\alpha }_s\right)$ and the anomalous dimensions to next-to-leading order. The final expressions for the differential decay spectra include the complete $\mathcal{O}\left({\alpha }_s\right)$ corrections and sum the leading and next-to-leading Sudakov series. We present results for regions of phase space where the shape function can be expanded in local operators and give the matching coefficients of the resulting enhanced non-perturbative effects to order ${\alpha }_s.$ We show that moments of the shape function are not given by moments of local operators once perturbative effects are included, explain why the shape function and its moments satisfy different renormalization group equations, and contrast this with the situation for deep inelastic scattering. We show that there are large perturbative corrections in the usual definition of the shape function. This renders incorrect previous prescriptions for combining radiative corrections with the shape function.

We construct finite size, supersymmetric, tubular D-brane configurations with three charges, two angular momenta and several brane dipole moments. In type IIA string theory these are tubular configurations with D0, D4 and F1 charge, as well as D2, D6 and NS5 dipole moments. These multicharge generalizations of supertubes might have interesting consequences for the physics of the D1-D5-P black hole. We study the relation of the tubes to the spinning Breckenridge-Myers-Peet-Vafa black hole, and find that they have properties consistent with describing some of the hair of this black hole.

We consider the (1+1)-dimensional $\mathcal{N}=(2,2)\mathrm{}$ super Yang-Mills theory which is obtained by dimensionally reducing $\mathcal{N}=1\mathrm{}$ super Yang-Mills theory in four dimensions to two dimensions. We do our calculations in the large-$N_c$ approximation using supersymmetric discrete light cone quantization. The objective is to calculate quantities that might be investigated by researchers using other numerical methods. We present a precision study of the low-mass spectrum and the stress-energy correlator $〈T^{++}{\mathrm{}\left(r\right)T}^{++}\mathrm{}\left(0\right)\mathrm{}〉.$ We find that the mass gap of this theory closes as the numerical resolution goes to infinity and that the correlator in the intermediate r region behaves like $r^{-4.75}.$

A gauge-invariant field is found which describes physical configurations, i.e., gauge orbits, of non-Abelian gauge theories. This is accomplished with non-Abelian generalizations of the Poincaré-Hodge decomposition formula for one-forms. In a particular sense, the new field is dual to the gauge field. Using this field as a coordinate, the metric and intrinsic curvature are discussed for Yang-Mills orbit space for the (2+1)- and (3+1)-dimensional cases. The sectional, Ricci, and scalar curvatures are all formally non-negative. An expression for the new field in terms of the Yang-Mills connection is found in 2+1 dimensions. The measure on Schrödinger wave functionals is found in both 2+1 and 3+1 dimensions; in the former case, it resembles the Karabali, Kim, and Nair measure. We briefly discuss the form of the Hamiltonian in terms of the dual field and comment on how this is relevant to the mass gap for both the (2+1)- and (3+1)-dimensional cases.

We present two families of first-order in time and second-order in space formulations of the Einstein equations (variants of the Arnowitt-Deser-Misner formulation) that admit a complete set of characteristic variables and a conserved energy that can be expressed in terms of the characteristic variables. The associated constraint system is also symmetric hyperbolic in this sense, and all characteristic speeds are physical. We propose a family of constraint-preserving boundary conditions that is applicable if the boundary is smooth with tangential shift. We conjecture that the resulting initial-boundary value problem is well-posed.

Motivated by the initial-boundary value problem for the Einstein equations, we propose a definition of symmetric hyperbolicity for systems of evolution equations that are first order in time but second order in space. This can be used to impose constraint-preserving boundary conditions. The general methods are illustrated in detail in the toy model of electromagnetism.

The issue concerning rigorous methods recently developed in deriving the asymptotics of quasinormal modes is revisited and applied to a generic nonrotating multihorizon black holes solution. Some examples are illustrated and the single horizon cases are also considered. As a result, the asymptotics for large angular momentum parameter is shown to depend on the difference between the maximal or Nariai black hole mass and the ordinary black hole mass. The extremal limit is also discussed and the exact evaluation of the quasinormal frequencies related to the Nariai space-time is presented, as a consistent check of the general asymptotic formula.

Second-order formulations of the 3+1 Einstein equations obtained by eliminating the extrinsic curvature in terms of the time derivative of the metric are examined with the aim of establishing whether they are well posed, in cases of somewhat wide interest, such as ADM, BSSN and generalized Einstein-Christoffel. The criterion for well-posedness of second-order systems employed is due to Kreiss and Ortiz. By this criterion, none of the three cases are strongly hyperbolic, but some of them are weakly hyperbolic, which means that they may yet be well posed but only under very restrictive conditions for the terms of order lower than second in the equations (which are not studied here). As a result, intuitive transferences of the property of well-posedness from first-order reductions of the Einstein equations to their originating second-order versions are unwarranted if not false.

We study the dynamics of phantom model and give the conditions for potentials to admit tracking attractors, de Sitter attractors, and big rip attractors. In particular, we show that phantom models with exponential and inverse power law potentials do not admit the tracking attractor solution. The “tachyonic” stability of the system at/near the attractors as well as the quantum stability have been studied.

We show that cosmic acceleration can arise due to very tiny corrections to the usual gravitational action of general relativity, of the form $R^{-n}$ with $n>\mathrm{}0.\mathrm{}$ This model eliminates the need for a nonzero cosmological constant or any other form of dark energy, attributing a purely gravitational origin to the acceleration of the universe.

We compare the standard single scalar field inflationary predictions with those of an inflationary phase driven by a tachyon field. A slow-roll formalism is defined for tachyon inflation, and we derive the spectra of scalar and tensor perturbations as well as the consistency relations. At lowest order the predictions of standard and tachyon inflation are shown to be the same. Higher order deviations are present and their observational relevance is discussed. We then study some typical inflationary tachyon potentials, discuss their observational consequences and compare them with recent data. All the models predict a negative and very small running of the scalar spectral index, and they consistently lie within the $1\sigma$ contour of the data set. However, the regime of blue scalar spectral index and large gravity waves cannot be explored by these models. Finally, a new exact solution of the unperturbed and perturbed coupled gravity and tachyon equations is also presented.