Lectures on conformal field theory and Kac-Moody algebras

This is an introduction to the basic ideas and to a few further selected topics in conformal quantum field theory and in the theory of Kac-Moody algebras.Comment: 59 pages, LaTeX2e, extended version of lectures given at the Graduate Course on Conformal Field Theory and Integrable Models (Budapest, August 1996), to appear in Springer Lecture Notes in Physic

Microwave radiometer experiment of soil moisture sensing at BARC test site during summer 1981

Soil moisture was measured by truck mounted microwave radiometers at the frequencies of 1.4 GHz, 5 GHz, and 10.7 GHz. The soil textures in the two test sites were different so that the soil type effect of microwave radiometric response could be studied. Several fields in each test site were prepared with different surface roughnesses and vegetation covers. Ground truth on the soil moisture, temperature, and the biomass of the vegetation was acquired in support of the microwave radiometric measurements. Soil bulk density for each of the fields in both test sites was sampled. The soils in both sites were measured mechanically and chemically. A tabulation of the measured data is presented and the sensors and operational problems associated with the measurements are discussed

Influence of an Internal Magnetar on Supernova Remnant Expansion

Most of the proposed associations between magnetars and supernova remnant suffer from age problems. Usually, supernova remnants ages are determined from an approximation of the Sedov-Taylor phase relation between radius and age, for a fixed energy of the explosion ~ 10^{51} erg. Those ages do not generally agree with the characteristic ages of the (proposed) associated magnetars. We show quantitatively that, by taking into account the energy injected on the supernova remnant by magnetar spin-down, a faster expansion results, improving matches between characteristic ages and supernova remnants ages. However, the magnetar velocities inferred from observations would inviabilize some associations. Since characteristic ages may not be good age estimators, their influence on the likelihood of the association may not be as important. In this work we present simple numerical simulations of supernova remnants expansion with internal magnetars, and apply it to the observed objects. A short initial spin period, thought to be important for the very generation of the magnetic field, is also relevant for the modified expansion of the remnant. We next analyze all proposed associations case-by-case, addressing the likelyhood of each one, according to this perspective. We consider a larger explosion energy and reasses the characteristic age issue, and conclude that about 50% of the associations can be true ones, provided SGRs and AXPs are magnetars.Comment: 30 pages, AAStex, 5 figures, format fixe

Topological defects for the free boson CFT

Two different conformal field theories can be joined together along a defect line. We study such defects for the case where the conformal field theories on either side are single free bosons compactified on a circle. We concentrate on topological defects for which the left- and right-moving Virasoro algebras are separately preserved, but not necessarily any additional symmetries. For the case where both radii are rational multiples of the self-dual radius we classify these topological defects. We also show that the isomorphism between two T-dual free boson conformal field theories can be described by the action of a topological defect, and hence that T-duality can be understood as a special type of order-disorder duality.Comment: 43 pages, 4 figure

Recent progress constraining the nuclear equation of state from astrophysics and heavy ion reactions

The quest for the nuclear equation of state (EoS) at high densities and/or extreme isospin is one of the longstanding problems of nuclear physics. Ab initio calculations for the nuclear many-body problem make predictions for the density and isospin dependence of the EoS far away from the saturation point of nuclear matter. On the other hand, in recent years substantial progress has been mode to constrain the EoS both, from the astrophysical side and from accelerator based experiments. Heavy ion experiments support a soft EoS at moderate densities while recent neutron star observations require a ``stiff'' high density behavior. Both constraints are discussed and shown to be in agreement with the predictions from many-body theory.Comment: Invited talk given at NPA III, Dresden, Germany, March 200

When flux standards go wild: white dwarfs in the age of Kepler

White dwarf stars have been used as flux standards for decades, thanks to their staid simplicity. We have empirically tested their photometric stability by analyzing the light curves of 398 high-probability candidates and spectroscopically confirmed white dwarfs observed during the original Kepler mission and later with K2 Campaigns 0-8. We find that the vast majority (>97 per cent) of non-pulsating and apparently isolated white dwarfs are stable to better than 1 per cent in the Kepler bandpass on 1-hr to 10-d timescales, confirming that these stellar remnants are useful flux standards. From the cases that do exhibit significant variability, we caution that binarity, magnetism, and pulsations are three important attributes to rule out when establishing white dwarfs as flux standards, especially those hotter than 30,000 K.Comment: Accepted for publication in MNRAS; 7 pages, 4 figures, 2 table

Axial, induced pseudoscalar, and pion-nucleon form factors in manifestly Lorentz-invariant chiral perturbation theory

We calculate the nucleon form factors G_A and G_P of the isovector axial-vector current and the pion-nucleon form factor G_piN in manifestly Lorentz-invariant baryon chiral perturbation theory up to and including order O(p^4). In addition to the standard treatment including the nucleon and pions, we also consider the axial-vector meson a_1 as an explicit degree of freedom. This is achieved by using the reformulated infrared renormalization scheme. We find that the inclusion of the axial-vector meson effectively results in one additional low-energy coupling constant that we determine by a fit to the data for G_A. The inclusion of the axial-vector meson results in an improved description of the experimental data for G_A, while the contribution to G_P is small.Comment: 21 pages, 9 figures, REVTeX

Marginal deformations in string field theory

We describe a method for obtaining analytic solutions corresponding to exact marginal deformations in open bosonic string field theory. For the photon marginal deformation we have an explicit analytic solution to all orders. Our construction is based on a pure gauge solution where the gauge field is not in the Hilbert space. We show that the solution itself is nevertheless perfectly regular. We study its gauge transformations and calculate some coefficients explicitly. Finally, we discuss how our method can be implemented for other marginal deformations.Comment: 23 pages. v2: Some paragraphs improved, typos corrected, ref adde