We reexamine the projective light cone limit of the gauge-invariant Green-Schwarz action on five-dimensional anti–de Sitter $\otimes$ the five-sphere. It implies the usual holography for ${\mathrm{AdS}}_5,$ but also (a complex) one for ${\mathrm{S}}^5.$ The result is $N=4\mathrm{}$ projective superspace, which unlike $N=4\mathrm{}$ harmonic superspace can describe $N=4\mathrm{}$ super Yang-Mills theory off shell.

We study five dimensional brane physics induced by an O(2) texture formed in one extra dimension. The model contains two 3-branes of nonzero tension, and the extra dimension is compact. The symmetry-breaking scale of the texture controls the particle hierarchy between the two branes. The TeV-scale particles are confined to the negative-tension brane where the observer sees gravity as essentially four dimensional. The effect of massive Kaluza-Klein gravitons is suppressed.

We define the “maximally integrable” isotropic oscillator on ${\mathrm{CP}}^N$ and discuss its various properties, in particular, the behavior of the system with respect to a constant magnetic field. We show that the properties of the oscillator on ${\mathrm{CP}}^N$ qualitatively differ in the $N>\mathrm{}1\mathrm{}$ and $N=1\mathrm{}$ cases. In the former case we construct the “axially symmetric” system which is locally equivalent to the oscillator. We perform the Kustaanheimo-Stiefel transformation of the oscillator on ${\mathrm{CP}}^2$ and construct some generalized MIC-Kepler problem. We also define a $\mathcal{N}=2\mathrm{}$ superextension of the oscillator on ${\mathrm{CP}}^N$ and show that for $N>\mathrm{}1\mathrm{}$ the inclusion of a constant magnetic field preserves the supersymmetry of the system.

We construct lattices with alternating kinks and antikinks. The lattice is shown to be stable in certain models. We consider the forces between kinks and antikinks and find that the lattice dynamics is that of a Toda lattice. Such lattices are exotic metastable states in which the system can get trapped during a phase transition.

We study the exact renormalization group of the four dimensional ${\phi }^4$ theory perturbatively. We reformulate the differential renormalization group equations as integral equations that define the continuum limit of the theory directly with no need for a bare theory. We show how the self-consistency of the integral equations leads to the determination of the interaction vertices in the continuum limit. The inductive proof of the existence of a solution to the integral equations amounts to a proof of perturbative renormalizability, and it consists of nothing more than counting the scale dimensions of the interaction vertices. Universality is discussed within a context of the exact renormalization group.

In the framework of general relativity, a description of the matching conditions between two rotating perfect fluids spacetimes in terms of the kinematical properties of the fluids is introduced. The Einstein and Darmois equations are written using coordinates adapted to the boundary separating both spacetimes. The functions appearing in the equations have an immediate physical interpretation. The analysis is extended to the case of matching a perfect fluid spacetime (star interior) with a vacuum spacetime (gravitational field outside the star). By solving a boundary problem for a first order partial differential equation (“master equation”) we define an exterior tetrad such that the matching conditions and the Einstein equations, for this case, reproduce those of the two-fluid problem. The formalism is applied to a particular static spherically symmetric star and to the Kerr metric.

If the scale of quantum gravity is near a TeV, black holes will be copiously produced at the CERN LHC. In this work we study the main properties of the light descendants of these black holes. We show that the emitted partons are closely spaced outside the horizon, and hence they do not fragment into hadrons in vacuum but more likely into a kind of quark-gluon plasma. Consequently, the thermal emission occurs far from the horizon, at a temperature characteristic of the QCD scale. We analyze the energy spectrum of the particles emerging from the “chromosphere,” and find that the hard hadronic jets are almost entirely suppressed. They are replaced by an isotropic distribution of soft photons and hadrons, with hundreds of particles in the GeV range. This provides a new distinctive signature for black hole events at LHC.

We explore spherically symmetric stationary solutions, generated by “stars” with regular interiors, in purely massive gravity. We reexamine the claim that the resummation of nonlinear effects can cure, in a domain near the source, the discontinuity exhibited by the linearized theory as the mass m of the graviton tends to zero. First, we find analytical difficulties with this claim, which appears not to be robust under slight changes in the form of the mass term. Second, by numerically exploring the inward continuation of the class of asymptotically flat solutions, we find that, when m is “small,” they all end up in a singularity at a finite radius, well outside the source, instead of joining some conjectured “continuous” solution near the source. We reopen, however, the possibility of reconciling massive gravity with phenomenology by exhibiting a special class of solutions, with “spontaneous symmetry breaking” features, which are close, near the source, to general relativistic solutions and asymptote, for large radii, a de Sitter solution of curvature $\sim m^2.$

The so-called curvaton mechanism—a way to convert isocurvature perturbations into adiabatic ones—is investigated both analytically and numerically in a pre-big-bang scenario where the role of the curvaton is played by a sufficiently massive Kalb-Ramond axion of superstring theory. When combined with observations of CMBR anisotropies at large and moderate angular scales, the present analysis allows us to constrain quite considerably the parameter space of the model: in particular, the initial displacement of the axion from the minimum of its potential and the rate of evolution of the compactification volume during pre-big-bang inflation. The combination of theoretical and experimental constraints favors a slightly blue spectrum of scalar perturbations, and/or a value of the string scale in the vicinity of the SUSY GUT scale.

We discuss limits on the variation of ${(m}_q/{\Lambda }_{\mathrm{QCD}}).\mathrm{}$ The results are obtained by studying the $n-\alpha$ interaction during the big bang, Oklo natural nuclear reactor data, and limits on the variation of the proton g factor from quasar absorption spectra.

Low energy effective field theories motivated by string theory will likely contain several scalar moduli fields which will be relevant to early Universe cosmology. Some of these fields are expected to couple with nonstandard kinetic terms to other fields. In this paper, we study the splitting into adiabatic and isocurvature perturbations for a model with two scalar fields, one of which has a nonstandard kinetic term in the Einstein-frame action. Such actions can arise, e.g., in the pre-big-bang and ekpyrotic scenarios. The presence of a coupling through a nonstandard kinetic term induces a novel coupling between adiabatic and isocurvature perturbations which is nonvanishing when the potential for the matter fields is nonzero. This coupling is unsuppressed in the long wavelength limit and thus can lead to an important transfer of power from the entropy to the adiabatic mode on super-Hubble scales. We apply the formalism to the case of a previously found exact solution with an exponential potential and study the resulting mixing of adiabatic and isocurvature fluctuations in this example. We also discuss the possible relevance of the extra coupling in the perturbation equations for the process of generating an adiabatic component of the fluctuation spectrum from isocurvature perturbations without considering a later decay of the isocurvature component.

We consider cosmological inflation driven by the rolling tachyon in the context of the braneworld scenario. We show that sufficient inflation consistent with the observational constraints can be achieved for well defined upper limits on the five-dimensional mass scale, string mass scale and the string coupling for the bosonic string.

We reinvestigate the evolution of strongly degenerate neutrinos in the early universe. With the larger degeneracy, the neutrino number freezes at higher temperatures because the neutrino annihilation rate decreases. We consider a very large degeneracy, so large that the neutrino number freezes before the events in which the particle degrees of freedom in the universe decrease (e.g., the muon annihilation and the quark-hadron phase transition). In such a case, the degeneracy by the time of nucleosynthesis becomes smaller than the initial degeneracy. We calculate how much it decreases from the initial value on the basis of the conservation of the neutrino number and the total entropy. We find a large drop in the degeneracy, but it is not large enough to affect the current constraints on the neutrino degeneracy from big bang nucleosynthesis and cosmic microwave background.

In this paper two cosmological models representing the flat Friedmann universe filled with a Chaplygin fluid, with or without dust, are analyzed in terms of the recently proposed “statefinder” parameters. Trajectories of both models in the parameter plane are shown to be significantly different with respect to the “quiessence” and “tracker” models. The generalized Chaplygin gas model with an equation of state of the form $p=-A/{\rho }^{\alpha }$ is also analyzed in terms of the statefinder parameters.

We analyze the impact of certain modifications to short distance physics on the inflationary perturbation spectrum. For the specific case of power-law inflation, we find distinctive—and possibly observable—effects on the spectrum of density perturbations.

We carry out a covariant calculation of the measurable relativistic effects in an orbiting gyroscope experiment. The experiment, currently known as Gravity Probe B, compares the spin directions of an array of spinning gyroscopes with the optical axis of a telescope, all housed in a spacecraft that rolls about the optical axis. The spacecraft is steered so that the telescope always points toward a known guide star. We calculate the variation in the spin directions relative to readout loops rigidly fixed in the spacecraft, and express the variations in terms of quantities that can be measured, to sufficient accuracy, using an Earth-centered coordinate system. The measurable effects include the aberration of starlight, the geodetic precession caused by space curvature, the frame-dragging effect caused by the rotation of the Earth and the deflection of light by the Sun.

By mapping the signal-recycling (SR) optical configuration to a three-mirror cavity, and then to a single detuned cavity, we express the SR optomechanical dynamics, input–output relation, and noise spectral density in terms of only three characteristic parameters: the (free) optical resonant frequency and decay time of the entire interferometer, and the laser power circulating in the arm cavities. These parameters, and therefore the properties of the interferometer, are invariant under an appropriate scaling of SR-mirror reflectivity, SR detuning, arm-cavity storage time, and input power at the beam splitter. Moreover, so far the quantum-mechanical description of laser-interferometer gravitational-wave detectors, including radiation-pressure effects, has been obtained only at linear order in the transmissivity of arm-cavity internal mirrors. We relax this assumption and discuss how the noise spectral densities change.

Using $\mathrm{SU}{\mathrm{}\left(3\right)\mathrm{}}_c$ lattice QCD with the Kogut-Susskind fermion at the quenched level, we study the quark-gluon mixed condensate $g〈\overline{q}{\sigma }_{\mu \nu }{G}_{\mu \nu }q〉,$ which is another chiral order parameter. For each current quark mass, $m_q=21,36\mathrm{}$ and 52 MeV, we generate 100 gauge configurations in the ${16}^4$ lattice with $\beta =6.0,$ and perform the measurement of $g〈\overline{q}{\sigma }_{\mu \nu }{G}_{\mu \nu }q〉$ at 16 points in each gauge configuration. Using the 1600 data for each $m_q,$ we find $m_0^2\equiv g〈\overline{q}{\sigma }_{\mu \nu }{G}_{\mu \nu }q〉/〈\overline{q}q〉\simeq 2.5{\mathrm{GeV}}^2$ at the lattice scale in the chiral limit. The large value of $g〈\overline{q}{\sigma }_{\mu \nu }{G}_{\mu \nu }q〉$ suggests its importance in the operator product expansion in QCD.

We demonstrate that the Nambu-Goto string spectroscopy with massless quarks is replicated in highly excited states of the linear vector confinement potential. For deep radial excitations we observe that the Regge slope, spacing between daughter trajectories, and absolute state energies agree with those of the QCD string.