Finite Black Hole Entropy and String Theory

An accelerating observer sees a thermal bath of radiation at the Hawking temperature which is proportional to the acceleration. Also, in string theory there is a Hagedorn temperature beyond which one cannot go without an infinite amount of energy. Several authors have shown that in the context of Hawking radiation a limiting temperature for string theory leads to a limiting acceleration, which for a black hole implies a minimum distance from the horizon for an observer to remain stationary. We argue that this effectively introduces a cutoff in Rindler space or the Schwarzschild geometry inside of which accelerations would exceed this maximum value. Furthermore, this natural cutoff in turn allows one to define a finite entropy for Rindler space or a black hole as all divergences were occurring on the horizon. In all cases if a particular relationship exists between Newton's constant and the string tension then the entropy of the string modes agrees with the Bekenstein-Hawking formula.Comment: 17 pages, 1 figure, Florida Preprint UFIFT-HEP-94-0

Bethe Ansatz solution of the open XXZ chain with nondiagonal boundary terms

We propose a set of conventional Bethe Ansatz equations and a corresponding expression for the eigenvalues of the transfer matrix for the open spin-1/2 XXZ quantum spin chain with nondiagonal boundary terms, provided that the boundary parameters obey a certain linear relation.Comment: 11 pages, LaTeX; amssymb, amsmath, no figures; v2: citation adde

On the spin-liquid phase of one dimensional spin-1 bosons

We consider a model of one dimensional spin-1 bosons with repulsive density-density interactions and antiferromagnetic exchange. We show that the low energy effective field theory is given by a spin-charge separated theory of a Tomonaga-Luttinger Hamiltonian and the O(3) nonlinear sigma model describing collective charge and spin excitations respectively. At a particular ratio of the density-density to spin-spin interaction the model is integrable, and we use the exact solutions to provide an independent derivation of the low energy effective theory. The system is in a superfluid phase made of singlet pairs of bosons, and we calculate the long-distance asymptotics of certain correlation functions.Comment: 17 page

Neutrino Zero Modes on Electroweak Strings

Zero modes of massive standard model fermions have been found on electroweak Z-strings. A zero mode solution for a massless left-handed neutrino is also known, but was thought to be non-normalizable. Here we show that although this mode is not discretely normalizable, it is delta-function normalizable and the correct interpretation of this solution is within the framework of the continuum spectrum. We also analyze an extension of the standard model including right-handed neutrinos in which neutrinos have Dirac masses, arising from a Yukawa coupling to the usual SU(2) Higgs doublet, and right-handed Majorana masses. The Majorana mass terms are taken to be spatially homogeneous and are presumed to arise from the vacuum expectation value of some field acquired in a phase transition well above the electroweak phase transition. The resulting zero energy equations have a discrete zero mode.Comment: 5 pages, 1 figures, version to appear in Phys. Rev.

Exact Spectral Gaps of the Asymmetric Exclusion Process with Open Boundaries

We derive the Bethe ansatz equations describing the complete spectrum of the transition matrix of the partially asymmetric exclusion process with the most general open boundary conditions. By analysing these equations in detail for the cases of totally asymmetric and symmetric diffusion, we calculate the finite-size scaling of the spectral gap, which characterizes the approach to stationarity at large times. In the totally asymmetric case we observe boundary induced crossovers between massive, diffusive and KPZ scaling regimes. We further study higher excitations, and demonstrate the absence of oscillatory behaviour at large times on the ``coexistence line'', which separates the massive low and high density phases. In the maximum current phase, oscillations are present on the KPZ scale $t\propto L^{-3/2}$. While independent of the boundary parameters, the spectral gap as well as the oscillation frequency in the maximum current phase have different values compared to the totally asymmetric exclusion process with periodic boundary conditions. We discuss a possible interpretation of our results in terms of an effective domain wall theory.Comment: 42 pages, 25 figures; added appendix and minor correction

Sigma models as perturbed conformal field theories

We show that two-dimensional sigma models are equivalent to certain perturbed conformal field theories. When the fields in the sigma model take values in a space G/H for a group G and a maximal subgroup H, the corresponding conformal field theory is the $k\to\infty$ limit of the coset model $(G/H)_k$, and the perturbation is related to the current of G. This correspondence allows us for example to find the free energy for the "O(n)" (=O(n)/O(n-1)) sigma model at non-zero temperature. It also results in a new approach to the CP^{n} model.Comment: 4 pages. v2: corrects typos (including several in the published version

Integrable Ladder t-J Model with Staggered Shift of the Spectral Parameter

The generalization of the Yang-Baxter equations (YBE) in the presence of Z_2 grading along both chain and time directions is presented and an integrable model of t-J type with staggered disposition along a chain of shifts of the spectral parameter is constructed. The Hamiltonian of the model is computed in fermionic formulation. It involves three neighbour site interactions and therefore can be considered as a zig-zag ladder model. The Algebraic Bethe Ansatz technique is applied and the eigenstates, along with eigenvalues of the transfer matrix of the model are found. In the thermodynamic limit, the lowest energy of the model is formed by the quarter filling of the states by fermions instead of usual half filling.Comment: Latex2e with amsfonts package; 16 page