106 Matching Results

Search Results

Advanced search parameters have been applied.

Matter Unification in Warped Supersymmetric SO(10)

Description: We construct models of warped unification with a bulk SO(10) gauge symmetry and boundary conditions that preserve the SU(4)_C x SU(2)_L x SU(2)_R Pati-Salam gauge group (422). In the dual 4D description, these models are 422 gauge theories in which the apparent unification of gauge couplings in the minimal supersymmetric standard model is explained as a consequence of strong coupling in the ultraviolet. The weakness of the gauge couplings at low energies is ensured in this 4D picture by asymptotically non-free contributions from the conformal sector, which are universal due to an approximate SO(10) global symmetry. The 422 gauge symmetry is broken to the standard model group by a simple set of Higgs fields. An advantage of this setup relative to SU(5) models of warped unification is that matter is automatically required to fill out representations of 422, providing an elegant understanding of the quantum numbers of the standard-model quarks and leptons. The models also naturally incorporate the see-saw mechanism for neutrino masses and bottom-tau unification. Finally, they predict a rich spectrum of exotic particles near the TeV scale, including states with different quantum numbers than those that appear in SU(5) models.
Date: March 16, 2004
Creator: Nomura, Yasunori & Tucker-Smith, David
Partner: UNT Libraries Government Documents Department

Low energy gauge couplings in grand unified theories and high precision physics

Description: I generalize the leading log relations between low energy SU(3){sub QCD}, SU(2){sub {rvec I}} and U(l){sub Y} effective gauge couplings to include all one-loop threshold effects of matter fields in oblique vector self energy quantum corrections for both supersymmetric and non-supersymmetric SU(5) grand unified theories. These always involve an exactly conserved current from the unbroken SU(3){sub QCD} {times} U(L){sub QED} subgroup; this fact strongly constrains any non-decoupling of heavy states as well as the generic character of threshold effects. Relations between low energy gauge couplings depend on the details of the spectra of both the superheavy and low mass sectors; I display the common origin of the logs appropriate to superheavy matter states, which can be found with well known renormalization group techniques, and the combination of logs and polynomials appropriate for light matter states, which cannot. Relations between any two or all three low energy effective gauge couplings do not depend on the top quark or standard model Higgs` masses. Neither do they depend on neutral color singlet states such as other neutral color singlet Higgs` or higgsinos, neutrinos, zinos or photinos. Further, they do not depend on degenerate SU(5) matter representations, of either spin 0 or spin 1/2 of any mass; matter representations of SU(5) can affect such relations only if there is mass splitting within them. The b quark splitting from the {tau} and {nu}{sub {tau}} can affect the relation between gauge couplings for {vert_bar}q{sub 2}{vert_bar} {yields} m{sub b}{sup 2} as can hadronic resonances and multi-hadron states for lower {vert_bar}q{sub 2}{vert_bar}. New mass-split representations of light states, such as occur in supersymmetric theories, can also affect such relations.
Date: September 1, 1993
Creator: Lynn, B. W.
Partner: UNT Libraries Government Documents Department

Flavor tests of quark-lepton unification

Description: We could become convinced that a particular theory of very-high-energy physics is correct if (1) it has a tightly constrained structure and is linked strongly enough with observed particle interactions, or (2) it predicts new physics beyond the standard model which is discovered. The author makes the case that experiments of this decade and the next allow the possibility that we might become convinced that grand unification, a candidate theory of the second type, is correct.
Date: March 21, 1995
Creator: Hall, L. J.
Partner: UNT Libraries Government Documents Department

Probing the Planck Scale with Proton Decay

Description: We advocate the idea that proton decay may probe physics at the Planck scale instead of the GUT scale. This is possible because supersymmetric theories have dimension-5 operators that can induce proton decay at dangerous rates, even with R-parity conservation. These operators are expected to be suppressed by the same physics that explains the fermion masses and mixings. We present a thorough analysis of nucleon partial lifetimes in models with a string-inspired anomalous U(1)_X family symmetry which is responsible for the fermionic mass spectrum as well as forbidding R-parity violating interactions. Protons and neutrons can decay via R-parity conserving non-renormalizable superpotential terms that are suppressed by the Planck scale and powers of the Cabibbo angle. Many of the models naturally lead to nucleon decay near present limits without any reference to grand unification.
Date: April 28, 2004
Creator: Harnik, Roni; Larson, Daniel T.; Murayama, Hitoshi & Thormeier, Marc
Partner: UNT Libraries Government Documents Department

F-Theory Uplifts and GUTs

Description: We study the F-theory uplift of Type IIB orientifold models on compact Calabi-Yau threefolds containing divisors which are del Pezzo surfaces. We consider two examples defined via del Pezzo transitions of the quintic. The first model has an orientifold projection leading to two disjoint O7-planes and the second involution acts via an exchange of two del Pezzo surfaces. The two uplifted fourfolds are generically singular with minimal gauge enhancements over a divisor and, respectively, a curve in the non-Fano base. We study possible further degenerations of the elliptic fiber leading to F-theory GUT models based on subgroups of E{sub 8}.
Date: August 26, 2010
Creator: Blumenhagen, Ralph; /Munich, Max Planck Inst.; Grimm, Thomas W.; U., /Bonn; Jurke, Benjamin; /Munich, Max Planck Inst. et al.
Partner: UNT Libraries Government Documents Department

Texture of fermion mass matrices in partially unified theories

Description: We investigate the texture of fermion mass matrices in theories with partial unification (for example, SU(2){sub L} {times} SU(2){sub R} {times} SU(4){sub c}) at a scale of {approximately} 10{sup 12} GeV. Starting with the low energy values of the masses and the mixing angles, we find only two viable textures with at most four texture zeros. One of these corresponds to a somewhat modified Fritzsch textures. A theoretical derivation of these textures leads to new interesting relations among the masses and the mixing angles. 13 refs.
Date: December 31, 1996
Creator: Dutta, B. & Nandi, S.
Partner: UNT Libraries Government Documents Department

Bit-string physics: A novel theory of everything

Description: We encode the quantum numbers of the standard model of quarks and leptons using constructed bitstrings of length 256. These label a grouting universe of bit-strings of growing length that eventually construct a finite and discrete space-time with reasonable cosmological properties. Coupling constants and mass ratios, computed from closure under XOR and a statistical hypothesis, using only {h_bar}, c and m{sub p} to fix our units of mass, length and time in terms of standard (meterkilogram-second) metrology, agree with the first four to seven significant figures of accepted experimental results. Finite and discrete conservation laws and commutation relations insure the essential characteristics of relativistic quantum mechanics, including particle-antiparticle pair creation. The correspondence limit in (free space) Maxwell electromagnetism and Einstein gravitation is consistent with the Feynman-Dyson-Tanimura ``proof.``
Date: August 1, 1994
Creator: Noyes, H.P.
Partner: UNT Libraries Government Documents Department

Leptophobic Z{prime} from superstring derived models

Description: It was recently suggested that the reported anomalies in R{sub b} and R{sub c} can be interpreted as the effect of a heavy vector boson that couples to quarks and is universally decoupled from leptons. We examine how an extra gauge boson with this property can arise from superstring derived models. In a specific three generation model we show that the U(1){sub B-L} symmetry combines with the horizontal flavor symmetries to form a universal leptophobic U(1) symmetry. In our model there is an enhancement of the color gauge group from twisted sectors. The enhancement occurs after the breaking of the unifying gauge symmetry by ``Wilson lines.`` The leptophobic U(1) symmetry then becomes a generator of the color SU(4) gauge group. We examine how similar symmetries may appear in other string models without the enhancement. We propose that if the current LEP anomalies persist it may be evidence for a certain class of un-unified superstring models. 15 refs., 4 tabs.
Date: April 1, 1996
Creator: Faraggi, A.E. & Masip, M.
Partner: UNT Libraries Government Documents Department

{mu}{sup +} {yields} e{sup +}{gamma} and related rare decays

Description: The connection of rare decays to supersymmetric grand unification is highlighted, and a brief review of the status of rare decay experiments is given. The status of the MEGA experiment, a search for {mu}{sup +} {yields} e{sup +}{gamma}, is reported. Some ideas for a new experimental arrangement that has the potential to reach a sensitivity of 10{sup {minus}14} are presented.
Date: February 1, 1997
Creator: Cooper, M.D.
Partner: UNT Libraries Government Documents Department

Exotic leptoquarks from superstring derived models

Description: The H1 and ZEUS collaborations have recently reported a significant excess of e{sup +}p {r_arrow} e{sup +} jet events at high Q{sup 2}. While there exists insufficient data to conclusively determine the origin of this excess, one possibility is that it is due to a new leptoquark at mass scale around 200 GeV. We examine the type of leptoquark states that exist in superstring derived standard-like models, and show that, while these models may contain the standard leptoquark states which exist in Grand Unified Theories, they also generically contain new and exotic leptoquark states with fractional lepton number, {+-}1/2. In contrast to the traditional GUT-type leptoquark states, the couplings of the exotic leptoquarks to the Standard Model states are generated after the breaking of U(1){sub B-L}. This important feature of the exotic leptoquark states may result in local discrete symmetries which forbid some of the undesired leptoquark couplings. We examine these couplings in several models and study the phenomenological implications. The flavor symmetries of the superstring models are found to naturally suppress leptoquark flavor changing processes.
Date: March 1, 1997
Creator: Elwood, J.K. & Faraggi, A.E.
Partner: UNT Libraries Government Documents Department

Scalar mass relations and flavor violations in supersymmetric theories

Description: Supersymmetry provides the most promising solution to the gauge hierarchy problem. For supersymmetry to stablize the hierarchy, it must be broken at the weak scale. The combination of weak scale supersymmetry and grand unification leads to a successful prediction of the weak mixing angle to within 1{percent} accuracy. If supersymmetry is a symmetry of nature, the mass spectrum and the flavor mixing pattern of the scalar superpartners of all the quarks and leptons will provide important information about a more fundamental theory at higher energies. We studied the scalar mass relations which follow from the assumption that at high energies there is a grand unified theory which leads to a significant prediction of the weak mixing angle; these will serve as important tests of grand unified theories. Two intragenerational mass relations for each of the light generations are derived. A third relation is also found which relates the Higgs masses and the masses of all three generation scalars. In a realistic supersymmetric grand unified theory, nontrivial flavor mixings are expected to exist at all gaugino vertices. This could lead to important contributions to the neutron electric dipole moment, the decay mode p {r_arrow} K{sup 0}{mu}{sup +}, weak scale radiative corrections to the up-type quark masses, and lepton flavor violating signals such as {mu} {r_arrow} e{gamma}. These also provide important probes of physics at high energy scales. Supersymmetric theories involving a spontaneously broken flavor symmetry can provide a solution to the supersymmetric flavor-changing problem and an understanding of the fermion masses and mixings. We studied the possibilities and the general conditions under which some fermion masses and mixings can be obtained radiatively. We also constructed theories of flavor in which the first generation fermion masses arise from radiative corrections while flavor-changing constraints are satisfied. 69 refs., 19 figs., 9 tabs.
Date: May 9, 1996
Creator: Cheng, Hsin-Chia
Partner: UNT Libraries Government Documents Department

Report of the supersymmetry theory subgroup

Description: The authors provide a mini-guide to some of the possible manifestations of weak-scale supersymmetry. For each of six scenarios they provide: (1) a brief description of the theoretical underpinnings; (2) the adjustable parameters; (3) a qualitative description of the associated phenomenology at future colliders; (4) comments on how to simulate each scenario with existing event generators.
Date: June 1, 1996
Creator: Amundson, J.; Anderson, G. & Baer, H.
Partner: UNT Libraries Government Documents Department

The electroweak theory

Description: After a short essay on the current state of particle physics, the author reviews the antecedents of the modern picture of the weak and electromagnetic interactions and then undertakes a brief survey of the SU(2){sub L} {circle_times} U(1){sub Y} electroweak theory. The authors reviews the features of electroweak phenomenology at tree level and beyond, presents an introduction to the Higgs boson and the 1-TeV scale, and examines arguments for enlarging the electroweak theory. The author concludes with a brief look at low-scale gravity.
Date: August 10, 2001
Creator: Quigg, Chris
Partner: UNT Libraries Government Documents Department

On the anomalous U(1) in free fermionic superstring models

Description: The realistic free fermionic models have had an intriguing success in explaining different properties of the observed particle spectrum. In this paper the authors discuss in some detail the anomalous U(1) symmetry which exists in these models. They study the properties of the anomalous U(1) in both the more realistic NAHE-based free fermionic models and those in a general NAHE class. Appearance of an anomalous U(1) in the more realistic NAHE models is shown to be an effect of reduction of world-sheet supersymmetry from (2,2) to (2,0). They show, however, that in more general (2,1) and (2,0) models, all U(1) can remain anomaly-free under certain conditions. Several phenomenological issues related to the anomalous U(1) are discussed. In particular, they note that in some examples the anomalous U(1) arises from the breaking E{sub 6} {yields} SO(10) {times} U(1){sub A}, resulting in U(1){sub A} being family universal.
Date: November 1, 1997
Creator: Cleaver, G.B. & Faraggi, A.E.
Partner: UNT Libraries Government Documents Department

Consequences of an Abelian family symmetry

Description: The addition of an Abelian family symmetry to the Minimal Super-symmetric Standard Model reproduces the observed hierarchies of quark and lepton masses and quark mixing angles, only if it is anomalous. Green-Schwarz compensation of its anomalies requires the electroweak mixing angle to be sin{sup 2}{theta}{sub {omega}} = 3/8 at the string scale, without any assumed GUT structure, suggesting a superstring origin for the standard model. The analysis is extended to neutrino masses and the lepton mixing matrix.
Date: January 1, 1996
Creator: Ramond, P.
Partner: UNT Libraries Government Documents Department

The heavy top quark and supersymmetry

Description: Three aspects of supersymmetric theories are discussed: electroweak symmetry breaking, the issues of flavor, and gauge unification. The heavy top quark plays an important, sometimes dominant, role in each case. Additional symmetries lead to extensions of the standard model which can provide an understanding for many of the outstanding problems of particle physics. A broken supersymmetric extension of spacetime allows electroweak symmetry breaking to follow from the dynamics of the heavy top quark; an extension of isospin provides a constrained framework for understanding the pattern of quark and lepton masses; and a grand unified extension of the standard model gauge group provides an elegant understanding of the gauge quantum numbers of the components of a generation. Experimental signatures for each of these additional symmetries are discussed.
Date: May 8, 1996
Creator: Hall, L.J.
Partner: UNT Libraries Government Documents Department

Supersymmetric Grand Unified Models without Adjoint Higgs Fields

Description: We discuss two classes of supersymmetric grand unified theories based on extended gauge groups SO(10) x SO(10) and SO(10) x SO(10) x SO(10). Effective adjoint fields of each gauge group SO(10) are argued to be formed from combining two Higgs fields in fundamental representation of the extended gauge groups, one obtaining its VEV along the diagonal SO(10){sub D} direction and the other acquiring its VEV along the diagonal SU(5){sub D} x U(1){sub D} or its subgroup direction. Thus experimentally acceptable fermion mass matrices, such as Georgi-Jarlskog ansatz, with successful GUT mass relations can be constructed in these theories.
Date: June 23, 1999
Creator: Chou , Chih-Lung
Partner: UNT Libraries Government Documents Department

Overview of Grand Unified Models and their predictions for neutrino oscillations

Description: A brief overview of Grand Unified Models is presented with some attention paid to their predictions for neutrino oscillations. Given the well-known features of the two non-unified standard models, SM and MSSM, a listing of the features of classes of unified models is given, where a GUT flavor symmetry and/or family symmetry are introduced to reduce the number of model parameters. Some general remarks are then made concerning the type of predictions that follow for the neutrino masses and mixings.
Date: August 17, 2000
Creator: Albright, Carl H.
Partner: UNT Libraries Government Documents Department

Supersymmetry and supergravity: Phenomenology and grand unification

Description: A survey is given of supersymmetry and supergravity and their phenomenology. Some of the topics discussed are the basic ideas of global supersymmetry, the minimal supersymmetric Standard Model (MSSM) and its phenomenology, the basic ideas of local supersymmetry (supergravity), grand unification, supersymmetry breaking in supergravity grand unified models, radiative breaking of SU(2) {times} U(1), proton decay, cosmological constraints, and predictions of supergravity grand unified models. While the number of detailed derivations are necessarily limited, a sufficient number of results are given so that a reader can get a working knowledge of this field.
Date: December 31, 1993
Creator: Arnowitt, R. & Nath, P.
Partner: UNT Libraries Government Documents Department

Light Threshold Effects in Supersymmetric Grand Unified Theories

Description: Supersymmetric Grand Unified Theories have a rich spectrum of particles barely heavier than the intermediate vector bosons. As their non-supersymmetric counterparts, they lead to many relations among low energy observables. But the precise form of the predictions is modified by the extended spectrum. If the masses of these new particles are comparable to M{sub Z}, the standard computation of their effect becomes inaccurate. The authors, present a detailed discussion of the correct procedure, and carry out the relevant computations to one loop order. Attention is paid to the special treatment that the top and Higgs particles must receive. The size of the effect is explored for a range of parameters in the minimal supersymmetric SU(5) grand-unified theory with radiative breaking. It is found that the naive (leading-log) computation can be fairly inaccurate.
Date: August 1, 1993
Creator: Faraggi, A. E. & Grinstein, B.
Partner: UNT Libraries Government Documents Department

Reconstruction of fundamental SUSY parameters

Description: We summarize methods and expected accuracies in determining the basic low-energy SUSY parameters from experiments at future e{sup +}e{sup -} linear colliders in the TeV energy range, combined with results from LHC. In a second step we demonstrate how, based on this set of parameters, the fundamental supersymmetric theory can be reconstructed at high scales near the grand unification or Planck scale. These analyses have been carried out for minimal supergravity [confronted with GMSB for comparison], and for a string effective theory.
Date: September 25, 2003
Creator: al., P. M. Zerwas et
Partner: UNT Libraries Government Documents Department

Lepton family number violation

Description: At present there is evidence from neutrino oscillation searches that the neutrinos are in fact massive particles and that they mix. If confirmed, this would imply that the conservation of LFN is not exact. Lepton family number violation (LFNV) has been searched for with impressive sensitivities in many processes involving charged leptons. The present experimental limits on some of them (those which the author shall consider here) are shown in Table 1. These stringent limits are not inconsistent with the neutrino oscillation results since, given the experimental bounds on the masses of the known neutrinos and the neutrino mass squared differences required by the oscillation results, the effects of LFNV from neutrino mixing would be too small to be seen elsewhere (see Section 2). The purpose of experiments searching for LFNV involving the charged leptons is to probe the existence of other sources of LFNV. Such sources are present in many extensions of the SM. In this lecture the author shall discuss some of the possibilities, focusing on processes that require muon beams. Other LFNV processes, such as the decays of the kaons and of the {tau}, provide complementary information. In the next Section he shall consider some sources of LFNV that do not require an extension of the gauge group of the SM (the added leptons or Higgs bosons may of course originate from models with extended gauge groups). In Section 3 he discusses LFNV in left-right symmetric models. In Section 4 he considers LFNV in supersymmetric models, first in R-parity conserving supersymmetric grand unified models, and then in the minimal supersymmetric standard model with R-parity violation. The last section is a brief summary of the author`s conclusions.
Date: March 1, 1999
Creator: Herczeg, P.
Partner: UNT Libraries Government Documents Department

(S{sub 3}){sup 3} theories of flavor

Description: The author presents a supersymmetric theory of flavor based on the discrete flavor group (S{sub 3}){sup 3}. The model can account for the masses and mixing angles of the standard model, while maintaining sufficient sfermion degeneracy to evade the supersymmetric flavor problem. The author demonstrates that the model has a viable phenomenology and makes one very striking prediction: the nucleon decays predominantly to Kl where l is a first generation lepton. He shows that the modes n {yields} K{sup 0}{bar {nu}}{sub e}, p {yields} K{sup +}{bar {nu}}{sub e}, and p {yields} K{sup 0}e{sup +} occur at comparable rates, and could well be discovered simultaneously at the SuperKamiokande experiment.
Date: July 1, 1996
Creator: Carone, C.D.
Partner: UNT Libraries Government Documents Department

Outstanding junior investigator program. [Final technical report, 8/1/92-10/31/97]

Description: Much of the authors work over the past five years has been aimed at bridging the gap between the exactly supersymmetric world of string theories and the world that is actually observed. Her report discusses the following subjects: (1) supersymmetry breaking; related work on the mass hierarchy and the relation between supersymmetry and grand unified theories; distinguishing between supersymmetric models; and the fundamental question of how gauge theories arise from D-branes.
Date: December 18, 1999
Creator: Randall, Lisa & Rosenberg, Leslie
Partner: UNT Libraries Government Documents Department