Spontaneous formation of optically induced surface relief gratings

A model based on Fick's law of diffusion as a phenomenological description of the molecular motion, and on the coupled mode theory, is developped to describe single-beam surface relief grating formation in azopolymers thin films. It allows to explain the mechanism of spontaneous patterning, and self-organization. It allows also to compute the surface relief profile and its evolution in time with good agreement with experiments

Comments on Supergravity Description of S-branes

This is a note on the coupled supergravity-tachyon matter system, which has been earlier proposed as a candidate for the effective space-time description of S-branes. In particular, we study an ansatz with the maximal ISO(p+1)xSO(8-p,1) symmetry, for general brane dimensionality p and homogeneous brane distribution in transverse space \rho_\perp. A simple application of singularity theorems shows that (for p \le 7) the most general solution with these symmetries is always singular. (This invalidates a recent claim in the literature.) We include a few general comments about the possibility of describing the decay of unstable D-branes in purely gravitational terms.Comment: 19 pages, refs adde

Scalar Kaluza-Klein modes in a multiply warped braneworld

The Kaluza-Klein (KK) modes of a massive scalar field on a 3-brane embedded in six dimensional multiply warped spacetime are determined. Due to the presence of warping along both the extra dimensions the KK mass spectrum splits into two closely spaced branches which is a distinct feature of this model compared to the five dimensional Randall-Sundrum model. This new cluster of the KK mode spectrum is expected to have interesting phenomenological implications for the upcoming collider experiments. Such a scenario may also be extended for even larger number of orbifolded extra dimensions.Comment: 10 pages, Revte

Towards SDp-brane Quantization

The quantum mechanical analysis of the canonical hamiltonian description of the effective action of a SDp-brane in bosonic ten dimensional Type II supergravity in a homogeneous background is given. We find exact solutions for the corresponding quantum theory by solving the Wheeler-deWitt equation in the late-time limit of the rolling tachyon. The probability densities for several values of p are shown and their possible interpretation is discussed. In the process the effects of electromagnetic fields are also incorporated and it is shown that in this case the interpretation of tachyon regarded as ``matter clock'' is modified.Comment: 15 pages, 3 eps figures, revtex

Testing Hall-Post Inequalities With Exactly Solvable N-Body Problems

The Hall--Post inequalities provide lower bounds on $N$-body energies in terms of $N'$-body energies with $N'<N$. They are rewritten and generalized to be tested with exactly-solvable models of Calogero-Sutherland type in one and higher dimensions. The bound for $N$ spinless fermions in one dimension is better saturated at large coupling than for noninteracting fermions in an oscillatorComment: 7 pages, Latex2e, 2 .eps figure

Scattering of slow-light gap solitons with charges in a two-level medium

The Maxwell-Bloch system describes a quantum two-level medium interacting with a classical electromagnetic field by mediation of the the population density. This population density variation is a purely quantum effect which is actually at the very origin of nonlinearity. The resulting nonlinear coupling possesses particularly interesting consequences at the resonance (when the frequency of the excitation is close to the transition frequency of the two-level medium) as e.g. slow-light gap solitons that result from the nonlinear instability of the evanescent wave at the boundary. As nonlinearity couples the different polarizations of the electromagnetic field, the slow-light gap soliton is shown to experience effective scattering whith charges in the medium, allowing it for instance to be trapped or reflected. This scattering process is understood qualitatively as being governed by a nonlinear Schroedinger model in an external potential related to the charges (the electrostatic permanent background component of the field).Comment: RevTex, 14 pages with 5 figures, to appear in J. Phys. A: Math. Theo

No-Go Theorem for Horizon-Shielded Self-Tuning Singularities

We derive a simple no-go theorem relating to self-tuning solutions to the cosmological constant for observers on a brane, which rely on a singularity in an extra dimension. The theorem shows that it is impossible to shield the singularity from the brane by a horizon, unless the positive energy condition (rho+p >= 0) is violated in the bulk or on the brane. The result holds regardless of the kinds of fields which are introduced in the bulk or on the brane, whether Z_2 symmetry is imposed at the brane, or whether higher derivative terms of the Gauss-Bonnet form are added to the gravitational part of the action. However, the no-go theorem can be evaded if the three-brane has spatial curvature. We discuss explicit realizations of such solutions which have both self-tuning and a horizon shielding the singularity.Comment: 7 pages, 4 figures, revtex; added reference and minor correction

Tachyon Tunnelling in D-brane-anti-D-brane

Using the tachyon DBI action proposal for the effective theory of non-coincident D$_p$-brane-anti-D$_p$-brane system, we study the decay of this system in the tachyon channel. We assume that the branes separation is held fixed, i.e. no throat formation, and then find the bounce solution which describe the decay of the system from false to the true vacuum of the tachyon potential. We shall show that due to the non-standard form of the kinetic term in the effective action, the thin wall approximation for calculating the bubble nucleation rate gives a result which is independent of the branes separation. This unusual result might indicate that the true decay of this metastable system should be via a solution that represents a throat formation as well as the tachyon tunneling.Comment: 15 pages, 4 figures, Latex file, minor changes, reference adde

On the Relationship of Quantum Mechanics to Classical Electromagnetism and Classical Relativistic Mechanics

Some connections between quantum mechanics and classical physics are explored. The Planck-Einstein and De Broglie relations, the wavefunction and its probabilistic interpretation, the Canonical Commutation Relations and the Maxwell--Lorentz Equation may be understood in a simple way by comparing classical electromagnetism and the photonic description of light provided by classical relativistic kinematics. The method used may be described as `inverse correspondence' since quantum phenomena become apparent on considering the low photon number density limit of classical electromagnetism. Generalisation to massive particles leads to the Klein--Gordon and Schr\"{o}dinger Equations. The difference between the quantum wavefunction of the photon and a classical electromagnetic wave is discussed in some detail.Comment: 14 pages, no figures, no table