Exactly soluble model for self-gravitating D-particles with the wormhole

We consider D-particles coupled to the CGHS dilaton gravity and obtain the exact wormhole geometry and trajectories of D-particles by introducing the exotic matter. The initial static wormhole background is not stable after infalling D-particles due to the classical backreaction of the geometry so that the additional exotic matter source should be introduced for the stability. Then, the traversable wormhole geometry naturally appears and the D-particles can travel through it safely. Finally, we discuss the dynamical evolution of the wormhole throat and the massless limit of D-particles.Comment: 16 pages, 3 figures, revte

Quantum critical behavior induced by Mn impurity in CuGeO3

Results of high frequency (60-315 GHz) studies of ESR in CuGeO3 single crystals containing 0.9% of Mn impurity are reported. Quantitative EPR line shape analysis allowed concluding that low temperature magnetic susceptibility for T <40 K diverges following power law with the critical exponent 0.81 and therefore manifests onset of a quantum critical (QC) regime. We argue that transition into Griffiths phase occurs at TG~40 K and disorder produced by Mn impurity in quantum spin chains of CuGeO3 may lead to co-existence of the QC regime and spin-Peierls dimerisation.Comment: 2 pages, submitted to SCES05 proceeding

Accelerating Universes in String Theory via Field Redefinition

We study cosmological solutions in the effective heterotic string theory with $\alpha'$-correction terms in string frame. It is pointed out that the effective theory has an ambiguity via field redefinition and we analyze generalized effective theories due to this ambiguity. We restrict our analysis to the effective theories which give equations of motion of second order in the derivatives, just as "Galileon" field theory. This class of effective actions contains two free coupling constants. We find de Sitter solutions as well as the power-law expanding universes in our four-dimensional Einstein frame. The accelerated expanding universes are always the attractors in the present dynamical system.Comment: 22 pages, 3 figures, some additional formulae adde

Spinning and rotating strings for N=1 SYM theory and brane constructions

We obtain spinning and rotating closed string solutions in AdS_5 \times T^{1,1} background, and show how these solutions can be mapped onto rotating closed strings embedded in configurations of intersecting branes in type IIA string theory. Then, we discuss spinning closed string solutions in the UV limit of the Klebanov-Tseytlin background, and also properties of classical solutions in the related intersecting brane constructions in the UV limit. We comment on extensions of this analysis to the deformed conifold background, and in the corresponding intersecting brane construction, as well as its relation to the deep IR limit of the Klebanov-Strassler solution. We briefly discuss on the relation between type IIA brane constructions and their related M-theory descriptions, and how solitonic solutions are related in both descriptions.Comment: 35 pages. Dedicated to the memory of Ian I. Kogan. References adde

Abelian and nonabelian vector field effective actions from string field theory

The leading terms in the tree-level effective action for the massless fields of the bosonic open string are calculated by integrating out all massive fields in Witten's cubic string field theory. In both the abelian and nonabelian theories, field redefinitions make it possible to express the effective action in terms of the conventional field strength. The resulting actions reproduce the leading terms in the abelian and nonabelian Born-Infeld theories, and include (covariant) derivative corrections.Comment: 49 pages, 1 eps figur

Disorder driven quantum critical behavior in CuGeO3 doped with magnetic impurity

For the CuGeO3 doped with 1% of Fe the quantum critical behavior in a wide temperature range 1-40 K is reported. The critical exponents for susceptibility along different crystallographic axes are determined: a=0.34 (B//a and B//c) and a=0.31 (B//b). New effect of the frequency dependence of the critical exponent is discussed.Comment: Submitted to SCES0

Antiferromagnetic and van Hove Scenarios for the Cuprates: Taking the Best of Both Worlds

A theory for the high temperature superconductors is proposed. Holes are spin-1/2, charge e, quasiparticles strongly dressed by spin fluctuations. Based on their dispersion, it is claimed that the experimentally observed van Hove singularities of the cuprates are likely originated by antiferromagnetic (AF) correlations. From the two carriers problem in the 2D t-J model, an effective Hamiltonian for holes is defined with %no free parameters. This effective model has superconductivity in the ${\rm d_{x^2-y^2}}$ channel, a critical temperature ${\rm T_c \sim 100K}$ at the optimal hole density, ${\rm x=0.15}$, and a quasiparticle lifetime linearly dependent with energy. Other experimental results are also $quantitatively$ reproduced by the theory.Comment: 12 pages, 4 figures (on request), RevTeX (version 3.0), preprint NHMF

Continuous-distribution puddle model for conduction in trilayer graphene

An insulator-to-metal transition is observed in trilayer graphene based on the temperature dependence of the resistance under different applied gate voltages. At small gate voltages the resistance decreases with increasing temperature due to the increase in carrier concentration resulting from thermal excitation of electron-hole pairs. At large gate voltages excitation of electron-hole pairs is suppressed, and the resistance increases with increasing temperature because of the enhanced electron-phonon scattering. We find that the simple model with overlapping conduction and valence bands, each with quadratic dispersion relations, is unsatisfactory. Instead, we conclude that impurities in the substrate that create local puddles of higher electron or hole densities are responsible for the residual conductivity at low temperatures. The best fit is obtained using a continuous distribution of puddles. From the fit the average of the electron and hole effective masses can be determined.Comment: 18 pages, 5 figure

Time Evolution via S-branes

Using S(pacelike)-branes defined through rolling tachyon solutions, we show how the dynamical formation of D(irichlet)-branes and strings in tachyon condensation can be understood. Specifically we present solutions of S-brane actions illustrating the classical confinement of electric and magnetic flux into fundamental strings and D-branes. The role of S-branes in string theory is further clarified and their RR charges are discussed. In addition, by examining ``boosted'' S-branes, we find what appears to be a surprising dual S-brane description of strings and D-branes, which also indicates that the critical electric field can be considered as a self-dual point in string theory. We also introduce new tachyonic S-branes as Euclidean counterparts to non-BPS branes.Comment: 62 pages, 10 figures. v2 references adde

Inflationary Attractor from Tachyonic Matter

We study the complete evolution of a flat and homogeneous universe dominated by tachyonic matter. We demonstrate the attractor behaviour of the tachyonic inflation using the Hamilton-Jacobi formalism. We else obtain analytical approximations to the trajectories of the tachyon field in different regions. The numerical calculation shows that an initial non-vanishing momentum does not prevent the onset of inflation. The slow-rolling solution is an attractor.Comment: 4 pages, 2 figures, RevTe