arXiv subjects

G. A. Diamandis

Publications and source records attributed to G. A. Diamandis.

25 records · Page 2Linked to original sources

arXiv1999

On `Graceful Exit' from inflationary phase in two-dimensional Liouville String Cosmology

Within the context of a super-critical (Liouville) string, we discuss (target-space) two-dimensional string cosmology. A numerical analysis indicates that the identification of time with the Liouville mode results in an expanding universe with matter which exhibits an inflationary phase, and `graceful exit' from it, tending asymptotically to a flat-metric fixed point.This fixed point is characterized by a dilaton configuration which, depending on the initial conditions, either decreases linearly with the cosmic time, or is a finite constant. This implies that, in contrast to the critical string case, the string coupling remains bounded during the exit from the inflationary phase, and, thus, the pertinent dynamics can be reliably described in terms of a tree-level string effective action. The rôle of matter in inducing such phenomena is emphasized. It is also interesting to note that the asymptotic value of the vacuum energy, which in the $σ$-model framework is identified with the `running' central charge deficit, depends crucially on the set of initial conditions. Thus, although preliminary, this toy model seems to share all the features expected to characterize a phenomenologically acceptable cosmological string model.

hep-th↗

arXiv1997

Irreversible Time Flow in a Two-Dimensional Dilaton Black Hole with Matter

We show that an exact solution of two-dimensional dilaton gravity with matter discovered previously exhibits an irreversible temporal flow towards flat space with a vanishing cosmological constant. This time flow is induced by the back reaction of matter on the space-time geometry. We demonstrate that the system is not in equilibrium if the cosmological constant is non-zero, whereas the solution with zero cosmological constant is stable. The flow of the system towards this stable end-point is derived from the renormalization-group flow of the Zamolodchikov function. This behaviour is interpreted in terms of non-critical Liouville string, with the Liouville field identified as the target time.

gr-qc↗

arXiv1997

N=1 Supersymmetric Spin-Charge Separation in effective gauge theories of planar magnetic superconductors

We present a N=1 Supersymmetric extension of a spin-charge separated effective $SU(2)\times U_S(1)$ `particle-hole' gauge theory of excitations about the nodes of the gap of a d-wave planar magnetic superconductor. The supersymmetry is achieved without introducing extra degrees of freedom, as compared to the non-supersymmetric models. The only exception, the introduction of gaugino fieds, finds a natural physical interpretation as describing interlayer coupling in the statistical model. The low-energy continuum theory is described by a relativistic (2+1)-dimensional supersymmetric $CP^1$ $σ$-model with Gross-Neveu-Thirring-type four-fermion interactions. We emphasize the crucial rôle of the $CP^1$ constraint in inducing a non-trivial dynamical mass generation for fermions (and thus superconductivity), in a way compatible with manifest N=1 supersymmetry. We also give a preliminary discussion of non-perturbative effects. We argue that supersymmetry suppresses the dangerous for superconductivity instanton contributions to the mass of the perturbatively massless gauge boson of the unbroken U(1) subgroup of SU(2). Finally, we point out the possibility of applying these ideas to effective gauge models of spin-charge separation in one-space dimensional superconducting chains of holons, which, for example, have recently been claimed to be important in the stripe phase of underdoped cuprates.

cond-mat↗

arXiv1996

Backreaction Effects in the Two-Dimensional Dilaton Gravity

In this work we find static black hole solutions in the context of the two-dimensional dilaton gravity, which is modified by the addition of an $R^2$ term. This term arises from the one-loop effective action of a massive scalar field in its large mass expansion. The basic feature of this term is that it does not contribute to the Hawking radiation of the classical black hole backgrounds of the model. From this point of view a class of the solutions derived are interpreted as describing backreaction effects. In particular it is argued that evolution of a black hole via non-thermal signals is possible. Nevertheless this evolution seems to be 'soft', in the sense that it does not lead to the evaporation of a black hole, leaving the Hawking radiation as the dominant mechanism for this process.

hep-th↗

arXiv1995

Tachyon Field Quantization and Hawking Radiation

We quantize the tachyon field in a static two dimensional dilaton gravity black hole background,and we calculate the Hawking radiation rate. We find that the thermal radiation flux, due to the tachyon field, is larger than the conformal matter one. We also find that massive scalar fields which do not couple to the dilaton, do not give any contribution to the thermal radiation, up to terms quadratic in the scalar curvature.

hep-th↗

arXiv1994

Tachyon Effects on the 2-Dim Black Hole Geometry

We study solutions of the tree level string effective action in the presence of the tachyon mode.We find that the 2-dim. static black hole is stable against tachyonic perturbations.For a particular ansatz for the tachyon field we find an exact solution of the equations of motion which exhibits a naked singularity.In the case of static fields we find numerically that the full system has a black hole solution,with the tachyon regular at the horizon.

hep-th↗

arXiv1992

Time-dependent perturbations in two-dimensional String Black Holes

We discuss time-dependent perturbations (induced by matter fields) of a black-hole background in tree-level two-dimensional string theory. We analyse the linearized case and show the possibility of having black-hole solutions with time-dependent horizons. The latter exist only in the presence of time-dependent `tachyon' matter fields, which constitute the only propagating degrees of freedom in two-dimensional string theory. For real tachyon field configurations it is not possible to obtain solutions with horizons shrinking to a point. On the other hand, such a possibility seems to be realized in the case of string black-hole models formulated on higher world-sheet genera. We connect this latter result with black hole evaporation/decay at a quantum level.}

hep-th↗