Supersymmetric Brane World Scenarios from Off-Shell Supergravity

Using N=2 off-shell supergravity in five dimensions, we supersymmetrize the brane world scenario of Randall and Sundrum. We extend their construction to include supersymmetric matter at the fixpoints.Comment: 15 pages, no figures, late

Vacuum energy for the supersymmetric twisted D-brane in constant electromagnetic field

We calculate vacuum energy for twisted SUSY D-brane on toroidal background with constant magnetic or constant electric field. Its behaviour for toroidal D-brane (p=2) in constant electric field shows the presence of stable minimum for twisted versions of the theory. That indicates such a background maybe reasonable groundstate.Comment: LaTeX, 10 page

Raman scattering in a two-dimensional electron gas: Boltzmann equation approach

The inelastic light scattering in a 2-d electron gas is studied theoretically using the Boltzmann equation techniques. Electron-hole excitations produce the Raman spectrum essentially different from the one predicted for the 3-d case. In the clean limit it has the form of a strong non-symmetric resonance due to the square root singularity at the electron-hole frequency $\omega = vk$ while in the opposite dirty limit the usual Lorentzian shape of the cross section is reestablished. The effects of electromagnetic field are considered self-consistently and the contribution from collective plasmon modes is found. It is shown that unlike 3-d metals where plasmon excitations are unobservable (because of very large required transfered frequencies), the two-dimensional electron system gives rise to a low-frequency ($\omega \propto k^{1/2}$) plasmon peak. A measurement of the width of this peak can provide data on the magnitude of the electron scattering rate.Comment: 4 pages, 3 figures. to appear in Phys. Rev. B 59 (1999

Improved photometry of SDSS crowded field images: Structure and dark matter content in the dwarf spheroidal galaxy Leo I

We explore how well crowded field point-source photometry can be accomplished with SDSS data: We present a photometric pipeline based on DoPhot, and tuned for analyzing crowded-field images from the SDSS. Using Monte Carlo simulations we show that the completeness of source extraction is above 80% to i < 21 (AB) and a stellar surface density of about 200 sq.amin. Hence, a specialized data pipeline can efficiently be used for e.g. nearby resolved galaxies in SDSS images, where the standard SDSS photometric package Photo, when applied in normal survey mode, gives poor results. We apply our pipeline to an area of about 3.55sq.deg. around the dwarf spheroidal galaxy (dSph) Leo I, and construct a high S/N star-count map of Leo I via an optimized filter in color-magnitude space (g,r,i). Although the radial surface-density profile of the dwarf deviates from the best fit empirical King model towards outer radii, we find no evidence for tidal debris out to a stellar surface-density of 4*10^(-3) of the central value. We determine the total luminosity of Leo I, and model its mass using the spherical and isotropic Jeans equation. Assuming that 'mass follows light' we constrain a lower limit of the total mass of the dSph to be (1.7+/-0.2)*10^7 Msol. Contrary, if the mass in Leo I is dominated by a constant density dark-matter (DM) halo, then the mass within the central 12' is (2+/-0.6)*10^8 Msol. This leads to a mass-to-light ratio of >>6 (Ic_sol), and possibly >75 if the DM halo dominates the mass and extends further out than 12'. In summary, our results show that Leo I is a symmetric, relaxed and bound system; this supports the idea that Leo I is a dark-matter dominated system.Comment: 13 pages, 11 figures; accepted for publication in A

Universal contributions to scalar masses from five dimensional supergravity

We compute the effective Kahler potential for matter fields in warped compactifications, starting from five dimensional gauged supergravity, as a function of the matter fields localization. We show that truncation to zero modes is inconsistent and the tree-level exchange of the massive gravitational multiplet is needed for consistency of the four-dimensional theory. In addition to the standard Kahler coming from dimensional reduction, we find the quartic correction coming from integrating out the gravity multiplet. We apply our result to the computation of scalar masses, by assuming that the SUSY breaking field is a bulk hypermultiplet. In the limit of extreme opposite localization of the matter and the spurion fields, we find zero scalar masses, consistent with sequestering arguments. Surprisingly enough, for all the other cases the scalar masses are tachyonic. This suggests the holographic interpretation that a CFT sector always generates operators contributing in a tachyonic way to scalar masses. Viability of warped su- persymmetric compactifications necessarily asks then for additional contributions. We discuss the case of additional bulk vector multiplets with mixed boundary conditions, which is a partic- ularly simple and attractive way to generate large positive scalar masses. We show that in this case successful fermion mass matrices implies highly degenerate scalar masses for the first two generations of squarks and sleptons.Comment: 23 pages. v2: References added, new section on effect of additional bulk vector multiplets and phenomenolog

On orbifold theory and N=2, D=5 gauged supergravity

We have studied the most general N=2 supergravity in five dimensions in context with the orbifold theory based on $M_4 \times S^1/Z_2$. Various ways to treat the supersymmetry with singular sources placed in orbifold fixed points were proposed in past. Supersymmetric branes were consistently introduced in a bulk where a gauged supergravity was present. In this paper we find that in the $N=2,D=5$ supergravity with general gauging, the possibility to obtain a supersymmetric brane world is constrained. Imposing the compatibility of supersymmetry transformation rules with the orbifold condition, we find the necessary and sufficient condition to obtain supersymmetric branes and bulk independently. We comment that the same condition guarantees naturally the presence of singular BPS solutions.Comment: 16 page

Sleep Problems in Early Childhood and Early Onset of Alcohol and Other Drug Use in Adolescence

Background : No prospective studies exist on the relationship between sleep problems early in life and subsequent alcohol use. Stimulated by the adult literature linking sleep problems to the subsequent onset of alcohol use disorders in some adults, we examined whether sleep problems in early childhood predicted the onset of alcohol and other drug use in adolescence and whether such a relationship was mediated by other known predictors of this relationship, namely, attention problems, anxiety/depression, and aggression in late childhood. Methods : This study is part of an ongoing longitudinal study of the development of risk for alcohol and other substance use disorders. Study participants were 257 boys from a community-recruited sample of high-risk families. Results : Mothers’ ratings of their children's sleep problems at ages 3 to 5 years significantly predicted an early onset of any use of alcohol, marijuana, and illicit drugs, as well as an early onset of occasional or regular use of cigarettes by age 12 to 14. Additionally, although sleep problems in early childhood also predicted attention problems and anxiety/depression in later childhood, these problems did not mediate the relationship between sleep problems and onset of alcohol and other drug use. Conclusions : This is, to our knowledge, the first study that prospectively examines the relationship between sleep problems and early onset of alcohol use, a marker of increased risk for later alcohol problems and alcohol use disorders. Moreover, early childhood sleep problems seem to be a robust marker for use of drugs other than alcohol. Implications for the prevention of early alcohol and other drug use are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65934/1/01.ALC.0000121651.75952.39.pd

Reduced brain activation during inhibitory control in children with COMT Val/Val genotype

IntroductionBehavioral undercontrol is a well‐established risk factor for substance use disorder, identifiable at an early age well before the onset of substance use. However, the biological mechanistic structure underlying the behavioral undercontrol/substance use relationship is not well understood. The enzyme catechol O‐methyltransferase (COMT) catabolizes dopamine and norepinephrine in the prefrontal cortex and striatum, brain regions involved in behavioral control. The goal of this work was to investigate the association between genetic variation in COMT functioning and fronto‐striatal brain functioning during successful inhibitory control, a critical aspect of behavioral control.MethodsParticipants were 65 (22 female) 7–12 year olds who were genotyped for the functional COMT Val158Met (rs4680) single‐nucleotide polymorphism and underwent functional magnetic resonance imaging while performing a go/no‐go task. The majority of the sample (80%) had at least one parent with a history of alcohol use disorder and were thus at heightened risk for substance use disorders.ResultsThere was a significant main effect of genotype on brain activation in left and right putamen during successful versus failed inhibition and in right inferior frontal gyrus/insula during successful inhibition versus baseline. Follow‐up tests revealed that Met homozygotes had greater activation in each region relative to Val homozygotes.ConclusionsThese results are relevant for understanding how specific genes influence brain functioning related to underlying risk factors for substance use disorders and other disinhibitory psychopathologies.The goal of this work was to investigate the association between genetic variation in COMT functioning and fronto‐striatal brain functioning during inhibitory control, a critical aspect of behavioral control. Participants were 65 (22 female) 7–12 year olds who were genotyped for the functional COMT Val158Met (rs4680) single‐nucleotide polymorphism and underwent functional magnetic resonance imaging while performing a go/no‐go task. There was a significant main effect of genotype on brain activation in left and right putamen during successful versus failed inhibition and in right inferior frontal gyrus/insula during successful inhibition versus baseline; follow‐up tests revealed that Met homozygotes had greater activation in each region relative to Val homozygotes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135697/1/brb3577_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135697/2/brb3577.pd

Ultracompact, low-loss directional couplers on InP based on self-imaging by multimode interference

We report extremely compact (494-µm-long 3 dB splitters, including input/output bends), polarization-insensitive, zero-gap directional couplers on InP with a highly multimode interference region that are based on the self-imaging effect. We measured cross-state extinctions better than 28 dB and on-chip insertion losses of 0.5 dB/coupler plus 1 dB/cm guide propagation loss at 1523 nm wavelength

The Smallest Mass Ratio Young Star Spectroscopic Binaries

Using high resolution near-infrared spectroscopy with the Keck telescope, we have detected the radial velocity signatures of the cool secondary components in four optically identified pre-main-sequence, single-lined spectroscopic binaries. All are weak-lined T Tauri stars with well-defined center of mass velocities. The mass ratio for one young binary, NTTS 160905-1859, is M2/M1 = 0.18+/-0.01, the smallest yet measured dynamically for a pre-main-sequence spectroscopic binary. These new results demonstrate the power of infrared spectroscopy for the dynamical identification of cool secondaries. Visible light spectroscopy, to date, has not revealed any pre-main-sequence secondary stars with masses <0.5 M_sun, while two of the young systems reported here are in that range. We compare our targets with a compilation of the published young double-lined spectroscopic binaries and discuss our unique contribution to this sample.Comment: Accepted for publication in the April, 2002, ApJ; 6 figure