States of Low Energy on Bianchi I spacetimes

States of Low Energy are a class of exact Hadamard states for free quantum fields on cosmological spacetimes whose structure is fixed at {\it all} scales by a minimization principle. The original construction was for Friedmann-Lema\^{i}tre geometries and is here generalized to anisotropic Bianchi I geometries relevant to primordial cosmology. In addition to proving the Hadamard property systematic series expansions in the infrared and ultraviolet are developed. The infrared expansion is convergent and induces in the massless case a leading spatial long distance decay that is always Minkowski-like but anisotropy modulated. For the ultraviolet expansion a non-recursive formula for the coefficients is presented.Comment: 44 page

Quantized Einstein-Rosen waves, AdS_2, and spontaneous symmetry breaking

4D cylindrical gravitational waves with aligned polarizations (Einstein-Rosen waves) are shown to be described by a weight 1/2 massive free field on the double cover of AdS_2. Thorn's C-energy is one of the sl(2,R) generators, the reconstruction from the (timelike) symmetry axis is the CFT_1 holography. Classically the phase space is also invariant under a O(1,1) group action on the metric coefficients that is a remnant of the original 4D diffeomorphism invariance. In the quantum theory this symmetry is found to be spontaneously broken while the AdS_2 conformal invariance remains intact.Comment: 13 pages, Latex, 2 Figures. v2: Figure on AdS added, minor change

The Quantum Spectrum of the Conserved Charges in Affine Toda Theories

The exact eigenvalues of the infinite set of conserved charges on the multi-particle states in affine Toda theories are determined. This is done by constructing a free field realization of the Zamolodchikov-Faddeev algebra in which the conserved charges are realized as derivative operators. The resulting eigenvalues are renormalization group (RG) invariant, have the correct classical limit and pass checks in first order perturbation theory. For $n=1$ one recovers the (RG invariant form of the) quantum masses of Destri and DeVega.Comment: 38p, 1 fig. included, MPI-Ph/93-92, LATE

Varying the Unruh Temperature in Integrable Quantum Field Theories

A computational scheme is developed to determine the response of a quantum field theory (QFT) with a factorized scattering operator under a variation of the Unruh temperature. To this end a new family of integrable systems is introduced, obtained by deforming such QFTs in a way that preserves the bootstrap S-matrix. The deformation parameter \beta plays the role of an inverse temperature for the thermal equilibrium states associated with the Rindler wedge, \beta = 2\pi being the QFT value. The form factor approach provides an explicit computational scheme for the \beta \neq 2\pi systems, enforcing in particular a modification of the underlying kinematical arena. As examples deformed counterparts of the Ising model and the Sinh-Gordon model are considered.Comment: 34 pages, Latex, 3 Figures, minor change

Form Factors, Thermal States and Modular Structures

Form factor sequences of an integrable QFT can be defined axiomatically as solutions of a system of recursive functional equations, known as ``form factor equations''. We show that their solution can be replaced with the study of the representation theory of a novel algebra F(S). It is associated with a given two-particle S-matrix and has the following features: (i) It contains a double TTS algebra as a subalgebra. (ii) Form factors arise as thermal vector states over F(S) of temperature 1/2\pi. The thermal ground states are in correspondence to the local operators of the QFT. (iii) The underlying `finite temperature structure' is indirectly related to the ``Unruh effect'' in Rindler spacetime. In F(S) it is manifest through modular structures (j,\delta) in the sense of algebraic QFT, which can be implemented explicitly in terms of the TTS generators.Comment: 40 pages, Latex. Simplification of the algebra and updat

An Algebraic Approach to Form Factors

An associative $*$-algebra is introduced (containing a $TTR$-algebra as a subalgebra) that implements the form factor axioms, and hence indirectly the Wightman axioms, in the following sense: Each $T$-invariant linear functional over the algebra automatically satisfies all the form factor axioms. It is argued that this answers the question (posed in the functional Bethe ansatz) how to select the dynamically correct representations of the $TTR$-algebra. Applied to the case of integrable QFTs with diagonal factorized scattering theory a universal formula for the eigenvalues of the conserved charges emerges.Comment: A simplified form of the algebra is used that allows one to dispense with the extra generator C. To appear in Nucl. Phys.

Dimensionally reduced gravity theories are asymptotically safe

4D Einstein gravity coupled to scalars and abelian gauge fields in its 2-Killing vector reduction is shown to be quasi-renormalizable to all loop orders at the expense of introducing infinitely many essential couplings. The latter can be combined into one or two functions of the `area radius' associated with the two Killing vectors. The renormalization flow of these couplings is governed by beta functionals expressible in closed form in terms of the (one coupling) beta function of a symmetric space sigma-model. Generically the matter coupled systems are asymptotically safe, that is the flow possesses a non-trivial UV stable fixed point at which the trace anomaly vanishes. The main exception is a minimal coupling of 4D Einstein gravity to massless free scalars, in which case the scalars decouple from gravity at the fixed point.Comment: 47 pages, Latex, 1 figur

Questionable and unquestionable in the perturbation theory of non-Abelian models

We show, by explicit computation, that bare lattice perturbation theory in the two-dimensional O(n) nonlinear $\sigma$ models with superinstanton boundary conditions is divergent in the limit of an infinite number of points $|\Lambda|$. This is the analogue of David's statement that renormalized perturbation theory of these models is infrared divergent in the limit where the physical size of the box tends to infinity. We also give arguments which support the validity of the bare perturbative expansion of short-distance quantities obtained by taking the limit $|\Lambda|\to\infty$ term by term in the theory with more conventional boundary conditions such as Dirichlet, periodic, and free.Comment: One reference added to the published version, 28 pages, 3 figure

Renormalization and asymptotic safety in truncated quantum Einstein gravity

A perturbative quantum theory of the 2-Killing vector reduction of general relativity is constructed. Although non-renormalizable in the standard sense, we show that to all orders of the loop expansion strict cut-off independence can be achieved in a space of Lagrangians differing only by a field dependent conformal factor. In particular the Noether currents and the quantum constraints can be defined as finite composite operators. The form of the field dependence in the conformal factor changes with the renormalization scale and a closed formula is obtained for the beta functional governing its flow. The flow possesses a unique fixed point at which the trace anomaly is shown to vanish. The approach to the fixed point adheres to Weinberg's ``asymptotic safety'' scenario, both in the gravitational wave/cosmological sector and in the stationary sector.Comment: 67 pages, Latex; v3: improved discussion of stationary sector; agrees with published versio

Comparison of the O(3) Bootstrap σ\sigma-Model with the Lattice Regularization at Low Energies

The renormalized coupling \gr defined through the connected 4-point function at zero external momentum in the non-linear O(3) sigma-model in two dimensions, is computed in the continuum form factor bootstrap approach with estimated error $\sim 0.3$. New high precision data are presented for \gr in the lattice regularized theory with standard action for nearly thermodynamic lattices $L/\xi\sim 7$ and correlation lengths $\xi$ up to $\sim 122$ and with the fixed point action for correlation lengths up to $\sim 12$. The agreement between the form factor and lattice results is within $\sim 1$. We also recompute the phase shifts at low energy by measuring the two-particle energies at finite volume, a task which was previously performed by L\"uscher and Wolff using the standard action, but this time using the fixed point action. Excellent agreement with the Zamolodchikov S-matrix is found.Comment: 23 pages, 4 figure