Universal Bounds in Even-Spin CFTs

We prove using invariance under the modular $S$- and $ST$-transformations that every unitary two-dimensional conformal field theory (CFT) of only even-spin operators (with no extended chiral algebra and with central charges $c,\tilde{c}>1$) contains a primary operator with dimension $\Delta_1$ satisfying $0 < \Delta_1 < (c+\tilde{c})/24 + 0.09280...$ After deriving both analytical and numerical bounds, we discuss how to extend our methods to bound higher conformal dimensions before deriving lower and upper bounds on the number of primary operators in a given energy range. Using the AdS$_3$/CFT$_2$ dictionary, the bound on $\Delta_1$ proves the lightest massive excitation in appropriate theories of 3D matter and gravity with cosmological constant $\Lambda < 0$ can be no heavier than $1/(8G_N)+O(\sqrt{-\Lambda})$; the bounds on the number operators are related via AdS/CFT to the entropy of states in the dual gravitational theory. In the flat-space approximation, the limiting mass is exactly that of the lightest BTZ black hole.Comment: arXiv admin note: text overlap with arXiv:0902.2790 by other authors; author note: this work is an extension of arXiv:0902.2790, please refer to it for additional details..new version has corrected typos and reference

Bounds on Operator Dimensions in 2D Conformal Field Theories

We extend the work of Hellerman (arxiv:0902.2790) to derive an upper bound on the conformal dimension $\Delta_2$ of the next-to-lowest nontrival primary operator in unitary two-dimensional conformal field theories without chiral primary operators. The bound we find is of the same form as found for $\Delta_1$: $\Delta_2 \leq c_{tot}/12 + O(1)$. We find a similar bound on the conformal dimension $\Delta_3$, and present a method for deriving bounds on $\Delta_n$ for any $n$, under slightly modified assumptions. For asymptotically large $c_{tot}$ and fixed $n$, we show that $\Delta_n \leq \frac{c_{tot}}{12}+O(1)$. We conclude with a brief discussion of the gravitational implications of these results.Comment: Corrected typos; revised arguments (adding detail) for clarity, results unchange

Violation of Kohler's rule by the magnetoresistance of a quasi-two-dimensional organic metal

The interlayer magnetoresistance of the quasi-two-dimensional metal $\alpha$-(BEDT-TTF)$_2$KHg(SCN)$_4$ is considered. In the temperature range from 0.5 to 10 K and for fields up to 10 tesla the magnetoresistance has a stronger temperature dependence than the zero-field resistance. Consequently Kohler's rule is not obeyed for any range of temperatures or fields. This means that the magnetoresistance cannot be described in terms of semiclassical transport on a single Fermi surface with a single scattering time. Possible explanations for the violations of Kohler's rule are considered, both within the framework of semi-classical transport theory and involving incoherent interlayer transport. The issues considered are similar to those raised by the magnetotransport of the cuprate superconductors.Comment: 5 pages, RevTeX + epsf, 2 figures. Slightly revised version to appear in Physical Review B, May 15, 199

Low-frequency method for magnetothermopower and Nernst effect measurements on single crystal samples at low temperatures and high magnetic fields

We describe an AC method for the measurement of the longitudinal (Sxx) and transverse (Sxy, i.e. Nernst) thermopower of mm-size single crystal samples at low temperatures (T30 T). A low-frequency (33 mHz) heating method is used to increase the resolution, and to determine the temperature gradient reliably in high magnetic fields. Samples are mounted between two thermal blocks which are heated by a sinusoidal frequency f0 with a p/2 phase difference. The phase difference between two heater currents gives a temperature gradient at 2f0. The corresponding thermopower and Nernst effect signals are extracted by using a digital signal processing method due. An important component of the method involves a superconducting link, YBa2Cu3O7+d (YBCO), which is mounted in parallel with sample to remove the background magnetothermopower of the lead wires. The method is demonstrated for the quasi two-dimensional organic conductor a-(BEDT-TTF)2KHg(SCN)4, which exhibits a complex, magnetic field dependent ground state above 22.5 T at low temperatures.Comment: 11 pages, 6 figures, 15 reference

Josephson plasma resonance in k-(BEDT-TTF)2Cu(NCS)2

A cavity perturbation technique is used to study the microwave response of the organic superconductor k-(BEDT-TTF)2Cu(NCS)2. Observation of a Josephson plasma resonance, below Tc (approx. 10 K), enables investigation of the vortex structure within the mixed state of this highly anisotropic, type-II, superconductor. Contrary to previous assumptions, frequency dependent studies (28 - 153 GHz) indicate that the squared plasma frequency depends exponentially on the magnetic field strength. Such behavior has been predicted for a weakly pinned quasi-two-dimensional vortex lattice [Bulaevskii et al. Phys. Rev. Lett. 74, 801 (1995)], but has not so far been observed experimentally. Our data also suggests a transition in the vortex structure near the irreversibility line not previously reported for an organic superconductor using this technique.Comment: 20 pages, including 5 figures. Revised version, accepted for publication in Phys. Rev.

Stardust Entry Reconstruction

An overview of the reconstruction analyses performed for the Stardust capsule entry is described. The results indicate that the actual entry was very close to the pre-entry predictions. The capsule landed 8.1 km north-northwest of the desired target at Utah Test and Training Range. Analyses of infrared video footage and radar range data (obtained from tracking stations) during the descent show that drogue parachute deployment was 4.8 s later than the pre-entry prediction, while main parachute deployment was 19.3 s earlier than the pre-set timer indicating that main deployment was actually triggered by the backup baroswitch. Reconstruction of a best estimated trajectory revealed that the aerodynamic drag experienced by the capsule during hypersonic flight was within 1% of pre-entry predications. Observations of the heatshield support the pre-entry estimates of small hypersonic angles of attack, since there was very little, if any, charring of the shoulder region or the aftbody. Through this investigation, an overall assertion can be made that all the data gathered from the Stardust capsule entry were consistent with flight performance close to nominal pre-entry predictions. Consequently, the design principles and methodologies utilized for the flight dynamics, aerodynamics, and aerothermodynamics analyses have been corroborated