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Heterotic orbifolds

Description: A review of orbifold geometry is given, followed by a review of the construction of four-dimensional heterotic string models by compactification on a six-dimensional Z{sub 3} orbifold. Particular attention is given to the details of the transition from a classical theory to a first-quantized theory. Subsequently, a discussion is given of the systematic enumeration of all standard-like three generation models subject to certain limiting conditions. it is found that the complete set is described by 192 models, with only five possibilities for the hidden sector gauge group. It is argued that only four of the hidden sector gauge groups are viable for dynamical supersymmetry breaking, leaving only 175 promising models in the class. General features of the spectra of matter states in all 175 models are discussed. Twenty patterns of representations are found to occur. Accommodation of the Minimal Supersymmetric Standard Model (MSSM) spectrum is addressed. States beyond those contains in the MSSM and nonstandard hypercharge normalization are shown to be generic, though some models do allow for the usual hypercharge normalization found in SU(5) embeddings of the Standard Model gauge group. Only one of the twenty patterns of representations, comprising seven of the 175 models, is found to be without an anomalous U(1). Various quantities of interest in effective supergravity model building are tabulated for the set of 175 models. String scale gauge coupling unification is shown to be possible, albeit contrived, in an example model.
Date: April 1, 2002
Creator: Giedt, Joel
Partner: UNT Libraries Government Documents Department

Modified fragmentation function and jet quenching at RHIC

Description: Medium modification of jet fragmentation functions and parton energy loss in cold and hot matter are reviewed. The predicted nuclear modification of the jet fragmentation function agrees well with the recent HERMES data with a resultant energy loss dE/dx {approx} 0.5 GeV/fm. From the recent PHENIX data of high p{sub T} pi{sub 0} spectra in central Au+Au collisions at {radical}s=130 GeV, one extracts an energy loss for a 10 GeV parton that is equivalent to dE/dx=7.3 GeV/fm in a static medium with the same gluon density as in the initial stage of the collision at tau{sub 0}=0.2 fm/c. Constraints on jet quenching by the central rapidity density of charged hadrons is also discussed.
Date: June 2, 2001
Creator: Wang, Xin-Nian
Partner: UNT Libraries Government Documents Department

Event by event fluctuations in heavy ion collisions

Description: The authors discuss the physics underlying event-by-event fluctuations in relativistic heavy ion collisions. We will argue that the fluctuations of the ratio of positively over negatively charged particles may serve as a unique signature for the Quark Gluon Plasma.
Date: January 1, 2001
Creator: Koch, Volker
Partner: UNT Libraries Government Documents Department

Noncommutative Geometry in M-Theory and Conformal Field Theory

Description: In the first part of the thesis I will investigate in the Matrix theory framework, the subgroup of dualities of the Discrete Light Cone Quantization of M-theory compactified on tori, which corresponds to T-duality in the auxiliary Type II string theory. After a review of matrix theory compactification leading to noncommutative supersymmetric Yang-Mills gauge theory, I will present solutions for the fundamental and adjoint sections on a two-dimensional twisted quantum torus and generalize to three-dimensional twisted quantum tori. After showing how M-theory T-duality is realized in supersymmetric Yang-Mills gauge theories on dual noncommutative tori I will relate this to the mathematical concept of Morita equivalence of C*-algebras. As a further generalization, I consider arbitrary Ramond-Ramond backgrounds. I will also discuss the spectrum of the toroidally compactified Matrix theory corresponding to quantized electric fluxes on two and three tori. In the second part of the thesis I will present an application to conformal field theory involving quantum groups, another important example of a noncommutative space. First, I will give an introduction to Poisson-Lie groups and arrive at quantum groups using the Feynman path integral. I will quantize the symplectic leaves of the Poisson-Lie group SU(2)*. In this way we obtain the unitary representations of U{sub q}(SU(2)). I discuss the X-structure of SU(2)* and give a detailed description of its leaves using various parametrizations. Then, I will introduce a new reality structure on the Heisenberg double of Fun{sub q} (SL(N,C)) for q phase, which can be interpreted as the quantum phase space of a particle on the q-deformed mass-hyperboloid. I also present evidence that the above real form describes zero modes of certain non-compact WZNW-models.
Date: May 1, 1999
Creator: Morariu, Bogdan
Partner: UNT Libraries Government Documents Department

Meson interferometry and the quest for quark-gluon matter

Description: We point out what we may learn from the investigation of identical two-particle interferometry in ultrarelativistic heavy ion collisions if we assume a particular model scenario by the formation of a thermalized quark-gluon plasma hadronizing via a first-order phase transition to an interacting hadron gas. The bulk properties of the two-pion correlation functions are dominated by these late and soft resonance gas rescattering processes. However, we show that kaons at large transverse momenta have several advantages and a bigger sensitivity to the QCD phase transition parameters.
Date: October 15, 2001
Creator: Soff, Sven
Partner: UNT Libraries Government Documents Department

Review of ion beam therapy: Present and Future

Description: First therapy efforts at the Bevalac using neon ions took place in the 70's and 80's. Promising results led to construction of HIMAC in Chiba Japan, and more recently to therapy trials at GSI. Both these facilities are now treating patients with carbon beams. Advances in both accelerator technology and beam delivery have taken place at these two centers. Plans are well along for new facilities in Europe and Japan.
Date: June 1, 2000
Creator: Alonso, Jose R.
Partner: UNT Libraries Government Documents Department

Antinucleus productions at RHIC

Description: Light antinuclei may be formed in relativistic heavy ion collisions via final state coalescence of antinucleons. The yields of antinuclei are sensitive to primordial antinucleon production, the volume of the system at kinetic freeze-out, and space-momentum correlations among antinucleons at freeze-out. We report here preliminary STAR results on {bar d} and {bar {sup 3}He} production in 130A GeV Au+Au collisions. These results are examined in a coalescence framework to elucidate the space-time structure of the antinucleon source.
Date: May 1, 2001
Creator: Hardtke, D. & Collaboration, STAR
Partner: UNT Libraries Government Documents Department

Dirichlet branes and nonperturbative aspects of supersymmetric string and gauge theories

Description: In chapter 1 the author reviews some elements of string theory relevant to the rest of this report. He touches on both the classical, i.e. perturbative, string physics before D-branes rise to prominence, and some of the progresses they brought forth. In chapter 2 he proceeds to give an exact algebraic formulation of D-branes in curved spaces. This allows one to classify them in backgrounds of interest and study their geometric properties. He applies this formalism to string theory on Calabi-Yau and other supersymmetry preserving manifolds. Then he studies the behavior of the D-branes under mirror symmetry in chapter 3. Mirror symmetry is known to be a symmetry of string theory perturbatively. He finds evidence for its nonperturbative validity when D-branes are also considered and compute some dynamical consequences. In chapter 4 he turns to examine the consistency of curved and/or intersecting D-brane configurations. They have been used recently to extract information about the field theories that arise in certain limits. It turns out that there are potential quantum mechanical inconsistencies associated with them. What saves the day are certain subtle topological properties of D-branes. This resolution has implications for the conserved charges carried by the D-branes, which he computes for the cases studied in chapter 2. In chapter 5 he uses intersecting brane configurations to study three dimensional supersymmetric gauge theories. There is also a mirror symmetry there that, among other things, exchanges classical and quantum mechanical quantities of a (mirror) pair of theories. It has an elegant realization in term of a symmetry of string theory involving D-branes. The author employs it to study a wide class of 3d models. He also predicts new mirror pairs and unconventional 3d field theories without Lagrangian descriptions.
Date: May 1, 1999
Creator: Yin, Zheng
Partner: UNT Libraries Government Documents Department

Big-bang nucleosynthesis with high-energy photon injection

Description: The author discusses the photodissociation of light elements due to the radiative decay of a massive particle, and he has shown how to constrain the model parameters from the observed light-element abundances. He adopted two quasar absorption system (QAS) D/H values, as well as solar system data for D/H and {sup 3}He/H. For each of these, he used two {sup 4}He values. He presents his results in terms of the confidence level at which each theoretical parameter set (i.e., the set of properties of a radiatively decaying particle) is excluded by the observed abundances. His algorithm for computing the confidence level is consistent and general enough to apply not only to the scenarios investigated in this work, but also to many other non-standard theories of BBN.
Date: May 1, 1999
Creator: Holtmann, Erich N.
Partner: UNT Libraries Government Documents Department

Spin clustering of accreting X-ray neutron stars as possible evidence of quark matter

Description: A neutron star in binary orbit with a low-mass non-degenerate companion becomes a source of x-rays with millisecond variability when mass accretion spins it up. Centrifugally driven changes in density profile may initiate a phase transition in a growing region of the core parallel to what may take place in an isolated millisecond pulsar, but in reverse. Such a star will spend a longer time in the spin frequency range over which the transition occurs than elsewhere because the change of phase, paced by the spinup rate, is accompanied by a growth in the moment of inertia. The population of accreters will exhibit a clustering in the critical frequency range. A phase change triggered by changing spin and the accompanying adjustment of moment of inertia has its analogue in rotating nuclei.
Date: June 27, 2001
Creator: Glendenning, Norman K. & Weber, Fridolin
Partner: UNT Libraries Government Documents Department

Introductory remarks: Reflections on the reasons for building accelerators

Description: This is a good occasion, just when Fermilab is considering whether or not to build a new machine, and just when KEK/JAERI has initiated a new machine, to look back in history and review the reasons given--even believed by the proponents--for constructing a new accelerator, and then look at what really happened. Now there is a fair amount of history, more than 80 years of it, as accelerators go back to the 20's. Perhaps it is useful to categorize accelerators into groups. The first might be Energy Frontier Machines. Now that, at first sight, might not be relevant, but it is. For a driver can be used to make neutrino beams of high energy and, of course, become the driver for a neutrino factory, and some day, perhaps, for a muon collider. Plenty of frontier things. The second category might be Special Purpose Machines, such as high intensity machines. Many of these are not in high energy physics, such as spallation sources, cyclotrons for nuclear physics, and medical accelerators. The relevance to this Workshop is obvious. A third category might be Machines for Advancing the Accelerator Art, where, once again, the relevance is obvious. There are machines built for political reasons. This is not a disparagement at all, for some of our most productive accelerators were built primarily for political reasons, such as building--or even maintaining--infra-structure in a country or a laboratory. The author mentions the political/sociological motives as we go along through the three categories that are inclusive of all accelerators. Now, there have been a great many accelerators, even in high energy physics, so the author isn't exhaustive here. The author just picks a few to give us what will be a balanced historical view.
Date: April 2, 2002
Creator: Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

Use of Taus in ATLAS

Description: The total production rate for taus at a hadron collider is not a useful quantity. Taus must have significant transverse momentum (p{sub T}) in order to be observable. Leptonic decays of taus will yield isolated electrons or muons that can be detected but these can also be directly produced so discriminating their origin can be difficult. Hadronic decays of taus result in jets that must be distinguished from jets arising from QCD processes using the particle multiplicity and invariant mass. At the LHC, new particles can be expected that decay to final states involving taus. Examples are given from simulations by the ATLAS experiment showing how such final states can be exploited.
Date: October 24, 2002
Creator: Hinchliffe, Ian
Partner: UNT Libraries Government Documents Department

Comparison of STIS and SNAP spectrograph throughputs

Description: This is a comparison of the measured throughput of STIS on HST versus what we might expect from the spectrograph on SNAP. The principle reference is Woodgate et al. (1998) PASP, 110, 1183. Additional material was taken from the STIS Handbook, available on-line at www.stsci.edu. The goal is to demonstrate that there are sound reasons to expect better performance for a SNAP spectrograph (even one with a grating) than would be expected by scaling from HST+STIS.
Date: June 30, 2002
Creator: Aldering, Greg
Partner: UNT Libraries Government Documents Department

SNAP sky background at the north ecliptic pole

Description: I summarize the extant direct and indirect data on the sky background SNAP will see at the North Ecliptic Pole over the wavelength range 0.4 < {lambda} < 1.7 {micro}m. At the spatial resolution of SNAP the sky background due to stars and galaxies is resolved, so the only source considered is zodiacal light. Several models are explored to provide interpolation in wavelength between the broadband data from HST and COBE observations. I believe the input data are now established well enough that the accuracy of the sky background presented here is sufficient for SNAP simulations, and that it will stand up to scrutiny by reviewers.
Date: July 1, 2002
Creator: Aldering, Greg
Partner: UNT Libraries Government Documents Department

Berkeley Off-line Radioisotope Generator (BORG)

Description: Development of chemical separations for the transactinides has traditionally been performed with longer-lived tracer activities purchased commercially. With these long-lived tracers, there is always the potential problem that the tracer atoms are not always in the same chemical form as the short-lived atoms produced in on-line experiments. This problem is especially severe for elements in groups 4 and 5 of the periodic table, where hydrolysis is present. The long-lived tracers usually are stored with a complexing agent to prevent sorption or precipitation. Chemistry experiments performed with these long-lived tracers are therefore not analogous to those chemical experiments performed in on-line experiments. One way to eliminate the differences between off-line and on-line chemistry experiments is through the use of a {sup 252}Cf fission fragment collection device. A {sup 252}Cf fission fragment collection device has already been constructed [1]. This device is limited in its capabilities. A new fission fragment device would allow the study of the chemical properties of the homologues of the heaviest elements. This new device would be capable of producing fission fragments for fast gas chemistry and aqueous chemistry experiments, long-lived tracers for model system development and neutrons for neutron activation. Fission fragment activities produced in this way should have the same chemical form as those produced in Cyclotron irradiations. The simple operation of this source will allow more rapid and reliable development of radiochemical separations with homologues of transactinide elements.
Date: July 23, 2001
Creator: Sudowe, Ralf & Patin, Joshua B.
Partner: UNT Libraries Government Documents Department

Strangeness and charm production in high energy heavy ion collisions

Description: We discuss the dynamical effects of strangeness and charm production in high energy nuclear collisions. In order to understand the early stage dynamical evolution, it is necessary to study the transverse momentum distributions of multi-strange hadrons like {Xi} and {Omega} and charm mesons like J/{Psi} as a function of collision centrality.
Date: January 1, 2001
Creator: Xu, Nu
Partner: UNT Libraries Government Documents Department

Quantum cosmology based on discrete Feynman paths

Description: Although the rules for interpreting local quantum theory imply discretization of process, Lorentz covariance is usually regarded as precluding time quantization. Nevertheless a time-discretized quantum representation of redshifting spatially-homogeneous universe may be based on discrete-step Feynman paths carrying causal Lorentz-invariant action--paths that not only propagate the wave function but provide a phenomenologically-promising elementary-particle Hilbert-space basis. In a model under development, local path steps are at Planck scale while, at a much larger ''wave-function scale'', global steps separate successive wave-functions. Wave-function spacetime is but a tiny fraction of path spacetime. Electromagnetic and gravitational actions are ''at a distance'' in Wheeler-Feynman sense while strong (color) and weak (isospin) actions, as well as action of particle motion, are ''local'' in a sense paralleling the action of local field theory. ''Nonmaterial'' path segments and ''trivial events'' collaborate to define energy and gravity. Photons coupled to conserved electric charge enjoy privileged model status among elementary fermions and vector bosons. Although real path parameters provide no immediate meaning for ''measurement'', the phase of the complex wave function allows significance for ''information'' accumulated through ''gentle'' electromagnetic events involving charged matter and ''soft'' photons. Through its soft-photon content the wave function is an ''information reservoir''.
Date: October 10, 2002
Creator: Chew, Geoffrey F.
Partner: UNT Libraries Government Documents Department

Impact of contributions of Glenn T. Seaborg on nuclear science

Description: Glenn Theodore Seaborg (1912-199) was a world-renowned nuclear chemist, a Nobel Laureate in chemistry in 1951, co-discoverer of plutonium and nine other transuranium elements, Chairman of the U.S. Atomic Energy Commission from 1961-71, scientific advisor to ten U.S. presidents, active in national and international professional societies, an advocate for nuclear power as well as for a comprehensive nuclear test ban treaty, a prolific writer, an avid hiker, environmentalist, and sports enthusiast. He was known and esteemed not only by chemists and other scientists throughout the world, but also by lay people, politicians, statesmen, and students of all ages. This memorial includes a brief glimpse of Glenn Seaborg's early life and education, describes some of his major contributions to nuclear science over his long and fruitful career, and highlights the profound impact of his contributions on nuclear science, both in the U.S. and in the international community.
Date: December 26, 2000
Creator: Hoffman, Darleane C.
Partner: UNT Libraries Government Documents Department

Electrodynamics at the highest energies

Description: At very high energies, the bremsstrahlung and pair production cross sections exhibit complex behavior due to the material in which the interactions occur. The cross sections in dense media can be dramatically different than for isolated atoms. This writeup discusses these in-medium effects, emphasizing how the cross section has different energy and target density dependencies in different regimes. Data from SLAC experiment E-146 will be presented to confirm the energy and density scaling. Finally, QCD analogs of the electrodynamics effects will be discussed.
Date: June 17, 2002
Creator: Klein, Spencer R.
Partner: UNT Libraries Government Documents Department

Spin clustering of accreting X-ray neutron stars as possible evidence of quark matter

Description: A neutron star in binary orbit with a low-mass non-degenerate companion becomes a source of x-rays with millisecond variability when mass accretion spins it up. Centrifugally driven changes in density profile may initiate a phase transition in a growing region of the core parallel to what may take place in an isolated millisecond pulsar, but in reverse. Such a star will spend a longer time in the spin frequency range over which the transition occurs than elsewhere because the change of phase, paced by the spinup rate, is accompanied by a growth in the moment of inertia. The population of accreters will exhibit a clustering in the critical frequency range. A phase change triggered by changing spin and the accompanying adjustment of moment of inertia has its analogue in rotating nuclei.
Date: June 27, 2001
Creator: Glendenning, Norman K. & Weber, Fridolin
Partner: UNT Libraries Government Documents Department

A Fundamental Theorem on Particle Acceleration

Description: A fundamental theorem on particle acceleration is derived from the reciprocity principle of electromagnetism and a rigorous proof of the theorem is presented. The theorem establishes a relation between acceleration and radiation, which is particularly useful for insightful understanding of and practical calculation about the first order acceleration in which energy gain of the accelerated particle is linearly proportional to the accelerating field.
Date: May 1, 2003
Creator: Xie, Ming
Partner: UNT Libraries Government Documents Department

Heavy ion physics at the LHC

Description: The ion-ion center of mass energies at the LHC will exceed that at RHIC by nearly a factor of 30, providing exciting opportunities for addressing unique physics issues in a completely new energy domain. Some highlights of this new physics domain are presented here. We briefly describe how these collisions will provide new insights into the high density, low momentum gluon content of the nucleus expected to dominate the dynamics of the early state of the system. We then discuss how the dense initial state of the nucleus affects the lifetime and temperature of the produced system. Finally, we explain how the high energy domain of the LHC allows abundant production of ''rare'' processes, hard probes calculable in perturbative quantum chromodynamics, QCD. At the LHC, high momentum jets and b{bar b} bound states, the {Upsilon} family, will be produced with high statistics for the first time in heavy ion collisions.
Date: August 15, 2004
Creator: Vogt, R.
Partner: UNT Libraries Government Documents Department