15,187 research outputs found
Non-supersymmetric Orientifolds of Gepner Models
Starting from a previously collected set of tachyon-free closed strings, we
search for N=2 minimal model orientifold spectra which contain the standard
model and are free of tachyons and tadpoles at lowest order. For each class of
tachyon-free closed strings -- bulk supersymmetry, automorphism invariants or
Klein bottle projection -- we do indeed find non-supersymmetric and tachyon
free chiral brane configurations that contain the standard model. However, a
tadpole-cancelling hidden sector could only be found in the case of bulk
supersymmetry. Although about half of the examples we have found make use of
branes that break the bulk space-time supersymmetry, the resulting massless
open string spectra are nevertheless supersymmetric in all cases. Dropping the
requirement that the standard model be contained in the spectrum, we find
chiral tachyon and tadpole-free solutions in all three cases, although in the
case of bulk supersymmetry all massless spectra are supersymmetric. In the
other two cases we find truly non-supersymmetric spectra, but a large fraction
of them are nevertheless partly or fully supersymmetric at the massless level.Comment: 13 pages, 4 figure
Classification of Simple Current Invariants
We summarize recent work on the classification of modular invariant partition
functions that can be obtained with simple currents in theories with a center
(Z_p)^k with p prime. New empirical results for other centers are also
presented. Our observation that the total number of invariants is
monodromy-independent for (Z_p)^k appears to be true in general as well. (Talk
presented in the parallel session on string theory of the Lepton-Photon/EPS
Conference, Geneva, 1991.)Comment: 8 page
Minimal Models from W-Constrained Hierarchies via the Kontsevich-Miwa Transform
A direct relation between the conformal formalism for 2d-quantum gravity and
the W-constrained KP hierarchy is found, without the need to invoke
intermediate matrix model technology. The Kontsevich-Miwa transform of the KP
hierarchy is used to establish an identification between W constraints on the
KP tau function and decoupling equations corresponding to Virasoro null
vectors. The Kontsevich-Miwa transform maps the -constrained KP
hierarchy to the minimal model, with the tau function being
given by the correlator of a product of (dressed) (or )
operators, provided the Miwa parameter and the free parameter (an
abstract spin) present in the constraints are expressed through the ratio
and the level .Comment: 11 pp REVISED (minor changes in the presentation, easier to read
The Adapted Ordering Method for Lie Algebras and Superalgebras and their Generalizations
In 1998 the Adapted Ordering Method was developed for the representation
theory of the superconformal algebras in two dimensions. It allows: to
determine maximal dimensions for a given type of space of singular vectors, to
identify all singular vectors by only a few coefficients, to spot subsingular
vectors and to set the basis for constructing embedding diagrams. In this
article we present the Adapted Ordering Method for general Lie algebras and
superalgebras, and their generalizations, provided they can be triangulated. We
also review briefly the results obtained for the Virasoro algebra and for the
N=2 and Ramond N=1 superconformal algebras.Comment: Many improvements in the redaction for pedagogical purposes. Latex,
11 page
The Impact of Insurance on the Law of Torts
An experimental study of "Model-on-Demand" (MoD) identification is made on a pilot-scale brine-water mixing tank. MoD estimation is compared against semi-physical modeling techniques using identification data generated from a systematically designed m-level Pseudo Random Sequence (PRS) input. The estimated models are the basis for evaluating the usefulness of MoD-based Model Predictive Control (MPC). For this application, MoD-MPC is shown to provide better performance at high bandwidths compared to a linear MPC controller
Constraints on extra dimensions from precision molecular spectroscopy
Accurate investigations of quantum level energies in molecular systems are
shown to provide a test ground to constrain the size of compactified extra
dimensions. This is made possible by the recent progress in precision metrology
with ultrastable lasers on energy levels in neutral molecular hydrogen (H,
HD and D) and the molecular hydrogen ions (H, HD and D).
Comparisons between experiment and quantum electrodynamics calculations for
these molecular systems can be interpreted in terms of probing large extra
dimensions, under which conditions gravity will become much stronger. Molecules
are a probe of space-time geometry at typical distances where chemical bonds
are effective, i.e. at length scales of an \AA. Constraints on compactification
radii for extra dimensions are derived within the Arkani-Hamed-Dimopoulos-Dvali
framework, while constraints for curvature or brane separation are derived
within the Randall-Sundrum framework. Based on the molecular spectroscopy of
D molecules and HD ions, the compactification size for seven extra
dimensions (in connection to M-theory defined in 11 dimensions) of equal size
is shown to be limited to m. While limits on compactification
sizes of extra dimensions based on other branches of physics are compared, the
prospect of further tightening constraints from the molecular method is
discussed
Investigation and Prosecution of Sexual Assault, Domestic Violence, and Stalking
This project examined sexual assault, domestic violence, and stalking cases reported to the Alaska State Troopers. More specifically, we examined all sexual assault and sexual abuse of minor incidents reported to Alaska State Troopers in 2003 and 2004, all assaults in domestic violence incidents reported to Alaska State Troopers in 2004, and all stalking incidents reported to Alaska State Troopers from 1994 to 2005. In addition, we examined whether cases were referred to the Alaska Department of Law for prosecution, were accepted for prosecution, and resulted in a conviction. This report provides a thorough overview of key characteristics on reports, suspects, victims, incidents, witnesses, and legal resolutions. This report also examines the predictors of legal resolutions. Finally, this report examines whether rural cases are less likely to have successful legal resolutions. Results clearly show that what Alaska State Troopers do when investigating reported offenses can increase rates of referral, acceptance, and conviction. In addition, we found no evidence of under-enforcement in rural areas. Contrary to allegations that the provision of criminal justice services is diminished in rural areas, we found that geographic isolation does not hinder case processing. These results are important for other rural jurisdictions. Most importantly, we found that cases first reported to local first responders had better legal resolutions. This finding suggests that the resources provided by these first responders (i.e., reduced response time and enhanced investigation) increase the rates of prosecutions and convictions. This finding is important not just in Alaska, but in other jurisdictions where official responders are not immediately available.National Institute of Justice, Office of Justice Programs, U.S. Department of Justice.
Grant No. 2005-WG-BX-0011I. Index of Tables and Figures / II. Acknowledgments / III. Executive Summary / IV. Goals and Background for this Study / V. State of Alaska / VI. Sexual Assault / VII. Domestic Violence / VIII. Stalking / IX. References / X. Appendice
Risk premium: insights over the threshold
The aim of this paper is twofold: First to test the adequacy of Pareto distributions to describe the tail of financial returns in emerging and developed markets, and second to study the possible correlation between stock market indices observed returns and return's extreme distributional characteristics measured by Value at Risk and Expected Shortfall. We test the empirical model using daily data from 41 countries, in the period from 1995 to 2005. The findings support the adequacy of Pareto distributions and the use of a log linear regression estimation of their parameters, as an alternative for the usually employed Hill's estimator. We also report a significant relationship between extreme distributional characteristics and observed returns, especially for developed countries
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