On the Canonical Formalism for a Higher-Curvature Gravity

Following the method of Buchbinder and Lyahovich, we carry out a canonical formalism for a higher-curvature gravity in which the Lagrangian density ${\cal L}$ is given in terms of a function of the salar curvature $R$ as ${\cal L}=\sqrt{-\det g_{\mu\nu}}f(R)$. The local Hamiltonian is obtained by a canonical transformation which interchanges a pair of the generalized coordinate and its canonical momentum coming from the higher derivative of the metric.Comment: 11 pages, no figures, Latex fil

Direct observation of the washboard noise of a driven vortex lattice in a high-temperature superconductor, Bi2Sr2CaCu2Oy

We studied the conduction noise spectrum in the vortex state of a high-temperature superconductor, Bi2Sr2CaCu2Oy, subject to a uniform driving force. Two characteristic features, a broadband noise (BBN) and a narrow-band noise (NBN), were observed in the vortex-solid phase. The origin of the large BBN was determined to be plastic motion of the vortices, whereas the NBN was found to originate from the washboard modulation of the translational velocity of the driven vortices. We believe this to be the first observation ofComment: 4 pages, 4 figures, to appear in Phys. Rev. Let

Direct perturbation theory on the shift of Electron Spin Resonance

We formulate a direct and systematic perturbation theory on the shift of the main paramagnetic peak in Electron Spin Resonance, and derive a general expression up to second order. It is applied to one-dimensional XXZ and transverse Ising models in the high field limit, to obtain explicit results including the polarization dependence for arbitrary temperature.Comment: 5 pages (no figures) in REVTE

A physical interpretation of the jet-like X-ray emission from supernova remnant W49B

In the framework of the study of supernova remnants and their complex interaction with the interstellar medium and the circumstellar material, we focus on the galactic supernova remnant W49B. Its morphology exhibits an X-ray bright elongated nebula, terminated on its eastern end by a sharp perpendicular structure aligned with the radio shell. The X-ray spectrum of W49B is characterized by strong K emission lines from Si, S, Ar, Ca, and Fe. There is a variation of the temperature in the remnant with the highest temperature found in the eastern side and the lowest one in the western side. The analysis of the recent observations of W49B indicates that the remnant may be the result of an asymmetric bipolar explosion where the ejecta are collimated along a jet-like structure and the eastern jet is hotter and more Fe-rich than the western one. Another possible scenario associates the X-ray emission with a spherical explosion where parts of the ejecta are interacting with a dense belt of ambient material. To overcome this ambiguity we present new results of the analysis of an XMM-Newton observation and we perform estimates of the mass and energy of the remnant. We conclude that the scenario of an anisotropic jet-like explosion explains quite naturally our observation results, but the association of W49B with a hypernova and a gamma-ray burst, although still possible, is not directly supported by any evidence.Comment: 7 pages, 5 figures, accepted for publication in Advances in Space Researc

Gravitational collapse in braneworld models with curvature corrections

We study the collapse of a homogeneous braneworld dust cloud in the context of the various curvature correction scenarios, namely, the induced-gravity, the Gauss-Bonnet, and the combined induced-gravity and Gauss-Bonnet. In accordance to the Randall-Sundrum model, and contrary to four-dimensional general relativity, we show in all cases that the exterior spacetime on the brane is non-static.Comment: References adde

Restrictions on dilatonic brane-world models

We consider dilatonic brane-world models with a non-minimal coupling between a dilaton and usual matter on a brane. We demonstrate that variation of the fundamental constants on the brane due to such interaction leads to strong restrictions on parameters of models. In particular, the experimental bounds on variation of the fine structure constant rule out non-minimal dilatonic models with a Liouville-type coupling potential f(varphi) = exp (b varphi) where b is order of 1.Comment: MiKTeX2-LaTeX2e, 10 pages, minor changes, improved references, to appear in IJMP

Optical studies of SN 2009jf: A type Ib supernova with an extremely slow decline and aspherical signature

Optical $UBVRI$ photometry and medium resolution spectroscopy of the type Ib supernova SN 2009jf, during the period $\sim -15$ to +250days with respect to the $B$ maximum are reported. The light curves are broad, with an extremely slow decline. The early post-maximum decline rate in the $V$ band is similar to SN 2008D, however, the late phase decline rate is slower than other studied type Ib supernovae. With an absolute magnitude of $M_{V} = -17.96\pm0.19$ magnitude at peak, SN 2009jf is a normally bright supernova. The peak bolometric luminosity and the energy deposition rate via $^{56}$Ni $\rightarrow$ $^{56}$Co chain indicate that $\sim {0.17}^{+0.03}_{-0.03}$ M$_{\odot}$ of $^{56}$Ni was ejected during the explosion. He\,I 5876 \AA\ line is clearly identified in the first spectrum of day $\sim -15$, at a velocity of $\sim 16000$ km sec$^{-1}$. The [O\,I] 6300-6364 \AA\ line seen in the nebular spectrum has a multi-peaked and asymmetric emission profile, with the blue peak being stronger. The estimated flux in this line implies \ga 1.34 M$_\odot$ oxygen was ejected. The slow evolution of the light curves of SN 2009jf indicates the presence of a massive ejecta. The high expansion velocity in the early phase and broader emission lines during the nebular phase suggest it to be an explosion with a large kinetic energy. A simple qualitative estimate leads to the ejecta mass of M$_{\rm ej} = 4-9$ M$_\odot$, and kinetic energy E$_{\rm K} = 3-8 \times 10^{51}$ erg. The ejected mass estimate is indicative of an initial main-sequence mass of \ga 20- 25 M$_\odot$.Comment: 14 pages, 13 figures; accepted for publication in MNRA

Magnetic von-Neumann lattice for two-dimensional electrons in the magnetic field

One-particle eigenstates and eigenvalues of two-dimensional electrons in the strong magnetic field with short range impurity and impurities, cosine potential, boundary potential, and periodic array of short range potentials are obtained by magnetic von-Neumann lattice in which Landau level wave functions have minimum spatial extensions. We find that there is a dual correspondence between cosine potential and lattice kinetic term and that the representation based on the von-Neumann lattice is quite useful for solving the system's dynamics.Comment: 21pages, figures not included, EPHOU-94-00

Nonlinear multidimensional cosmological models with form fields: stabilization of extra dimensions and the cosmological constant problem

We consider multidimensional gravitational models with a nonlinear scalar curvature term and form fields in the action functional. In our scenario it is assumed that the higher dimensional spacetime undergoes a spontaneous compactification to a warped product manifold. Particular attention is paid to models with quadratic scalar curvature terms and a Freund-Rubin-like ansatz for solitonic form fields. It is shown that for certain parameter ranges the extra dimensions are stabilized. In particular, stabilization is possible for any sign of the internal space curvature, the bulk cosmological constant and of the effective four-dimensional cosmological constant. Moreover, the effective cosmological constant can satisfy the observable limit on the dark energy density. Finally, we discuss the restrictions on the parameters of the considered nonlinear models and how they follow from the connection between the D-dimensional and the four-dimensional fundamental mass scales.Comment: 21 pages, LaTeX2e, minor changes, improved references, fonts include

Dynamical generation of a nontrivial index on the fuzzy 2-sphere

In the previous paper hep-th/0312199 we studied the 't Hooft-Polyakov (TP) monopole configuration in the U(2) gauge theory on the fuzzy 2-sphere and showed that it has a nonzero topological charge in the formalism based on the Ginsparg-Wilson relation. In this paper, by showing that the TP monopole configuration is stabler than the U(2) gauge theory without any condensation in the Yang-Mills-Chern-Simons matrix model, we will present a mechanism for dynamical generation of a nontrivial index. We further analyze the instability and decay processes of the U(2) gauge theory and the TP monopole configuration.Comment: Latex2e, 30 pages, 4 figures, the topological charge for a monopole configuration is corrected, reference added, the final version to appear in Physical Review D (the typos mentioned in the erratum are corrected