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What will we learn from the CMB?

Description: Within the next decade, experiments measuring the anisotropies in the cosmic microwave background (CMB) will add greatly to our knowledge of the universe. There are dozens of experiments scheduled to take data over the next several years, capped by the satellite missions of NASA (MAP) and ESA (PLANCK). What will we learn from these experiments? I argue that the potential pay-off is immense: We are quite likely to determine cosmological parameters to unprecedented accuracy. This will provide key information about the theory of structure formation and even about the physics behind inflation. If the experiments succeed, can anything spoil this pay-off? I focus on three possible spoilers - foregrounds, reionization, and defect models - and argue that we have every reason to be optimistic.
Date: October 1, 1997
Creator: Dodelson, S.
Partner: UNT Libraries Government Documents Department

Technicolor: status and prospects

Description: Technicolor models are briefly reviewed, and a number of promising signatures at hadron colliders are described. Low-scale technicolor should be discoverable in Run 11 of the Fermilab Tevatron; failing that, it would be hard to miss at the LHC. While technicolor models may be unfashionable, it is important to search for their signatures; we do not know how nature has chosen to break electroweak symmetry.
Date: September 1, 1997
Creator: Womersley, J.
Partner: UNT Libraries Government Documents Department

QSO color selection in the SDSS

Description: The Sloan Digital Sky Survey (SDSS) will image 10,000 square degrees in the north galactic cap in five filters. We hope to identify and obtain spectra for about 100,000 quasars brighter than 20th magnitude in this area. The selection will be primarily on the basis of point spread function and colors, but we will also identify quasars from a catalog of FIRST radio sources. The selection areas in color space must be determined during the testing period prior to the official start of the survey. This task may determine the length of the test period. In anticipation of this becoming the critical path, we have written a body of software that will allow us to quickly analyze a set of multicolor data and make a first cut at the selection limits.
Date: January 1, 1998
Creator: Newberg, H.J. & Yanny, B.
Partner: UNT Libraries Government Documents Department

Dealing with quantum weirdness: Holism and related issues

Description: Various issues are discussed in interpretation of quantum mechanics. All these explorations point toward the same conclusion, that some systems are holistically connected, i.e., some composite systems have properties that cannot, even in principle, be reduced to the properties of its subsystems. This is argued to be the central metaphysical lesson of quantum theory; this will remain pertinent even if quantum mechanics gets replaced by a superior theory. Chap. 2 discusses nonlocality and rules out hidden-variable theories that approximately reproduce the perfect correlations of quantum mechanics, as well as theories that obey locality conditions weaker than those needed to derive Bell`s inequality. Chap. 3 shows that SQUID experiments can rule out non-invasive measurability if not macrorealism. Chap. 4 looks at interpretational issues surrounding decoherence, the dissipative interaction between a system and its environment. Decoherence klcan help ``modal`` interpretations pick out the desired ``preferred`` basis. Chap. 5 explores what varieties of causation can and cannot ``explain`` EPR correlations. Instead of relying on ``watered down`` causal explanations, we should instead develop new, holistic explanatory frameworks.
Date: December 1, 1995
Creator: Elby, A.R.
Partner: UNT Libraries Government Documents Department

Gravitational microlensing results from MACHO

Description: The MACHO project is searching for dark qter inthe form of massive compact haio objects (Machos), by monitoring the brightness of millions of stars in the Magellanic Clouds to search for gravitational microlensing events. Analysis of our 1st 2.3 years of data for 8.5 million stars in the LMC yields 8 candidate microlensing events, well in excess of the {approx} 1 event expected from lensing by known low-mass stars. The event timescales range from 34 to 145 days, and the estimated optical depth is N 2x10{sup -7}, about half of that expected from a `standard` halo. Likelihood analysis indicates the typical lens mass is 0.5{sup +0.3}{sub -0.2}M{sub {circle_dot}}, suggesting they may be old white dwarfs.
Date: September 1, 1996
Creator: Alcock, C. & Collaboration, MACHO
Partner: UNT Libraries Government Documents Department

Universality and clustering in 1 + 1 dimensional superstring-bit models

Description: We construct a 1+1 dimensional superstring-bit model for D=3 Type IIB superstring. This low dimension model escapes the problem encountered in higher dimension models: (1) It possesses full Galilean supersymmetry; (2) For noninteracting Polymers of bits, the exactly soluble linear superpotential describing bit interactions is in a large universality class of superpotentials which includes ones bounded at spatial infinity; (3) The latter are used to construct a superstring-bit model with the clustering properties needed to define an S-matrix for closed polymers of superstring-bits.
Date: March 1, 1996
Creator: Bergman, O. & Thorn, C.B.
Partner: UNT Libraries Government Documents Department

Homoclinic orbits and chaos in a second-harmonic generating optical cavity

Description: We present two large families of Silnikov-type homoclinic orbits in a two mode-model that describes second-harmonic generation in a passive optical cavity. These families of homoclinic orbits give rise to chaotic dynamics in the model. 4 refs., 1 fig.
Date: April 1, 1997
Creator: Holm, D. & Kovacic, G., Timofeyev, I.
Partner: UNT Libraries Government Documents Department

Matrix membranes and integrability

Description: This is a pedagogical digest of results reported in Curtright, Fairlie, {ampersand} Zachos 1997, and an explicit implementation of Euler`s construction for the solution of the Poisson Bracket dual Nahm equation. But it does not cover 9 and 10-dimensional systems, and subsequent progress on them Fairlie 1997. Cubic interactions are considered in 3 and 7 space dimensions, respectively, for bosonic membranes in Poisson Bracket form. Their symmetries and vacuum configurations are explored. Their associated first order equations are transformed to Nahm`s equations, and are hence seen to be integrable, for the 3-dimensional case, by virtue of the explicit Lax pair provided. Most constructions introduced also apply to matrix commutator or Moyal Bracket analogs.
Date: June 1, 1997
Creator: Zachos, C.; Fairlie, D. & Curtright, T.
Partner: UNT Libraries Government Documents Department

A 2.14 ms candidate optical pulsar in SN1987A: Ten years after

Description: We have monitored Supernova 1987A in optical/near-infrared bands from a few weeks following its birth until the present time in order to search for a pulsar remnant. We have found an apparent pattern of emission near the frequency of 467.5 Hz - a 2.14 ms pulsar candidate, first detected in data taken on the remnant at the Las Campanas Observatory (LCO) 2.5-m Dupont telescope during 14-16 Feb. 1992 UT. We detected further signals near the 2.14 ms period on numerous occasions over the next four years in data taken with a variety of telescopes, data systems and detectors, at a number of ground- and space-based observatories. The sequence of detections of this signal from Feb. `92 through August `93, prior to its apparent subsequent fading, is highly improbable (< 10{sup -10} for any noise source). We also find evidence for modulation of the 2.14 ms period with a {approx}1,000 s period which, when taken with the high spindown of the source (2-3 x 10{sup -10} Hz/s), is consistent with precession and spindown via gravitational radiation of a neutron star with a non- axisymmetric oblateness of {approx}10{sup -6}, and an implied gravitational luminosity exceeding that of the Crab Nebula pulsar by an order of magnitude.
Date: September 1, 1997
Creator: Middleditch, J.; Kristian, J.A.; Kunkel, W.E.; Hill, K.M. & Watson, R.D.
Partner: UNT Libraries Government Documents Department

A Summary of the results obtained in the LDRD project "Interaction of a magnetized plasma with structured surfaces- from devices to spacecraft"

Description: Our work was directed towards developing a basic understanding of a new class of phenomena: effects of surface structure on the processes in a magnetized plasma near surfaces and at some distances for them. The surface structures can be of various kinds: topographic features ranging from smooth �waviness� to a coarse �roughness,� non-uniformities of the secondary emission coefficient, dielectric impregnations into conducting surface, etc. The expected effects are strongest when the magnetic field forms a shallow angle with the surface. The current and future applications of this new branch of plasma physics include fusion devices, gas-discharge and plasma-processing devices, large spacecraft, and physical phenomena in the vicinity of celestial bodies without atmospheres. We have developed a methodology that allows one to study in a unified way effects of rough surfaces with arbitrary scales of topographic features, from sizes exceeding the ion gyro-radius, to sizes much below the electron gyro-radius, in the most interesting case of a grazing magnetic field. The results can be presented in a dimensionless form, so that they would be equally applicable to the micrometer-scale roughness of the divertor plates of fusion devices, and to 10-km-scale structures of a Lunar surface. We have identified the following new effects: 1) the plasma is absorbed by only a small fraction of the total surface, near the �mountain tops� of the bumps; 2) regions inaccessible for one or both plasma species (�shadows�) are formed behind the bumps; the size of these inaccessible domains is, generally speaking, different for the electrons and ions; 3) this latter circumstance leads to formation of fine potential structure both near the surface and in the bulk plasma, leading to enhanced plasma transport. We have investigated the processes that may lead to plasma penetration into the shadows and concluded that most probable candidates are (depending on ...
Date: February 23, 1999
Creator: Cohen, R H; Porter, G D & Ryutov, D D
Partner: UNT Libraries Government Documents Department

MACHO RR lyrae stars in the galactic bulge: the spatial distribution

Description: We have analyzed a sample of 1150 type ab, and 550 type c RR Lyrae stars found in 24 bulge fields of the MACHO database. These fields cover a range in Galactocentric distances from 0.3 to 1.6 kpc. In combination with the data on the outer bulge fields of Alard (1997) and Wesselink (1987), here we present the surface density distribution of bulge RR Lyrae between 0.3 and 3 kpc. The distribution along the line of sight of the bulge RR Lyrae population was examined on the basis of the mean magnitudes, and it was shown that the bulk of the RR Lyrae population is not barred (Alcock et al. 1998). There is a hint of a bar only in the RR Lyrae of the inner fields closer to the Galactic center. The red giant clump stars in the MACHO fields, however, clearly show a barred distribution, confirming the results of previous studies (e.g. Dwek et al. 1995, Stanek et al. 1996). In the MACHO fields studied there are about 550 clump giants per RR Lyrae star. The RR Lyrae trace metal-poor stars, which are a minor component of the bulge population. The clump giants, however, should trace the bulk of the metal-rich population, foUowing underlying mass of the bulge more closely. Given the different spatial distribution, we concluded that the RR Lyrae and the clump giants trace two dif+erent populations (Alcock et al. 1998). The RR Lyrae would represent the inner extension of the Galactic halo in these fields (Minniti 1996). The observed surface distribution of RR Lyrae in the bulge fields was computed after discarding background RR Lyrae that belong to the Sgr dwarf galaxy (Alard 1996, Alcock et al. 1997). This distribution yields a power law density distribution. There is no turnover or flattening of this distribution ...
Date: August 1, 1997
Creator: Minniti, D.; Alcock, C. & Alves, D.
Partner: UNT Libraries Government Documents Department

Anisotropies in the cosmic microwave background: Theory

Description: Anisotropies in the Cosmic Microwave Background (CMB) contain a wealth of information about the past history of the universe and the present values of cosmological parameters. I online some of the theoretical advances of the last few years. In particular, I emphasize that for a wide class of cosmological models, theorists can accurately calculate the spectrum to better than a percent. The spectrum of anisotropies today is directly related to the pattern of inhomogeneities present at the time of recombination. This recognition leads to a powerful argument that will enable us to distinguish inflationary models from other models of structure formation. If the inflationary models turn out to be correct, the free parameters in these models will be determined to unprecedented accuracy by the upcoming satellite missions.
Date: February 1, 1998
Creator: Dodelson, S.
Partner: UNT Libraries Government Documents Department


Description: We review a class of dynamical models in which top condensation occurs at the weak scale, giving rise to the large top quark mass and other phenomena. This typically requires a color embedding, SU(3){sub c} {yields} SU(3){sub 1} x SU(3){sub 2}, ergo ``Topcolor.`` Topcolor suggests a novel route to technicolor models in which sequential quarks condense under the Topcolor interaction to break electroweak symmetries.
Date: November 1, 1996
Partner: UNT Libraries Government Documents Department

The CMBR spectrum

Description: Here we give an introduction to the observed spectrum of the Cosmic Microwave Background Radiation (CMBR) and discuss what can be learned about it. Particular attention will be given to how Compton scattering can distort the spectrum of the CMBR. An incomplete bibliography of relevant papers is also provided.
Date: May 1, 1997
Creator: Stebbins, A.
Partner: UNT Libraries Government Documents Department

Bayesian analysis of the solar neutrino anomaly

Description: We present an analysis of the recent solar neutrino data from the five experiments using Bayesian approach. We extract quantitative and easily understandable information pertaining to the solar neutrino problem. The probability distributions for the individual neutrino fluxes and, discrepancy distribution for B and Be fluxes, which include theoretical and experimental uncertainties have been extracted. The analysis carried out assuming that the neutrinos are unaltered during their passage from the sun to earth, clearly indicate that the observed PP flux is consistent with the 1995 standard solar model predictions of Bahcall and Pinsonneault within 2{sigma} (standard deviation), whereas the {sup 8}B flux is down by more than 12{sigma} and the {sup 7}Be flux is maximally suppressed. We also deduce the experimental survival probability for the solar neutrinos as a function of their energy in a model-independent way. We find that the shape of that distribution is in qualitative agreement with the MSW oscillation predictions.
Date: February 1, 1998
Creator: Bhat, C.M.
Partner: UNT Libraries Government Documents Department

Particle physics: Themes and challenges

Description: I will devote this lecture to seven themes that express the essence of our understanding and our possibilities. These themes are: elementarity, symmetry, consistency, unity, identity, opportunity, and relevance.
Date: November 1, 1995
Creator: Quigg, C.
Partner: UNT Libraries Government Documents Department

Science of consciousness and the hard problem

Description: Quantum theory is essentially a rationally coherent theory of the interaction of mind and matter, and it allows our conscious thoughts to play a causally efficacious and necessary role in brain dynamics. It therefore provides a natural basis, created by scientists, for the science of consciousness. As an illustration it is explained how the interaction of brain and consciousness can speed up brain processing, and thereby enhance the survival prospects of conscious organisms, as compared to similar organisms that lack consciousness. As a second illustration it is explained how, within the quantum framework, the consciously experienced {open_quotes}I{close_quotes} directs the actions of a human being. It is concluded that contemporary science already has an adequate framework for incorporating causally efficacious experimential events into the physical universe in a manner that: (1) puts the neural correlates of consciousness into the theory in a well defined way, (2) explains in principle how the effects of consciousness, per se, can enhance the survival prospects of organisms that possess it, (3) allows this survival effect to feed into phylogenetic development, and (4) explains how the consciously experienced {open_quotes}I{close_quotes} can direct human behaviour.
Date: May 22, 1996
Creator: Stapp, H.P.
Partner: UNT Libraries Government Documents Department

Large-scale mass power spectrum from peculiar velocities

Description: The power spectrum of mass density fluctuations is estimated from the Mark III and the SFI catalogs of peculiar velocities by applying a maximum likelihood analysis, using parametric models for the power spectrum and for the errors. Generalized CDM models with and without COBE normalization are used. The applications to the two different data sets give consistent results. The general result is a relatively high amplitude of the power spectrum, e.g., at k=0.1hMpc{sup -1} we find P(k){Omega}{sup 1.2}=(4.5{+-}2.0)x10{sup 3}(h{sup -1}Mpc){sup 3}, corresponding to {sigma}{sub 8}{Omega}{sup 0.6}=0.85{+-}0.2. Model-dependent constraints on combinations of cosmological parameters are obtained for families of COBE-normalized CDM models. these can roughly be approximated by {Omega}h{sub 60}{sup {mu}}n{sup {nu}}=0.6{+-}0.2, where {mu}=1.3 and {nu}=3.7, 2.0 for flat {Lambda}CDM models with and without tensor fluctuations respectively. For open CDM, without tensor fluctuations, the powers are {mu}=0.9 and {nu}=1.4. the quoted error-bars reflect the 90% formal likelihood uncertainty for each model and the variance among different models and between catalogs. This is a brief review of a collaborative project (for more details, see Zaroubi et al. 1997, Freudling et al. 1998). Preliminary constraints in the {Omega}-{Omega}{sub {Lambda}} plane are presented as well.
Date: October 1, 1998
Creator: Zehavi, Idit
Partner: UNT Libraries Government Documents Department

Error analysis for fast scintillator-based ICF burn history measurements

Description: Plastic scintillator material acts as a neutron-to-light converter in instruments that make ICF burn history measurements. Light output for a detected neutron has a fast rise time (420 ps) and a relatively long decay constant (1.2 ns). For a burst of neutrons whose duration is much shorter than the decay constant, instantaneous light output is approximately proportional to the integral of the neutron interaction rate with the scintillator material. Burn history is obtained by deconvolving the exponential decay from the recorded signal.
Date: July 6, 1998
Creator: Lerche, R A & Ognibene, T J
Partner: UNT Libraries Government Documents Department

An investigation of resonant photoemission in Gd with x-ray linear dichroism

Description: The constructive summing of direct and indirect channels above the absorption threshold of a core level can cause a massive increase in the emission cross section, leading to a phenomenon called "resonant photoemission". Using novel magnetic linear dichroism in angular distribution photoelectron spectroscopy experiments and theoretical simulations, we have probed the nature of the resonant photoemission process in Gd metal. It now appears that temporal matching as well as energy matching is a requirement for true resonant photoemission.
Date: July 1, 1998
Creator: Tobin, J G
Partner: UNT Libraries Government Documents Department