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Thomas W. Kephart

Publications and source records attributed to Thomas W. Kephart.

At least 127 records · Page 7Linked to original sources
arXiv2002

Black Holes, Mergers, and the Entropy Budget of the Universe

Vast amounts of entropy are produced in black hole formation, and the amount of entropy stored in supermassive black holes at the centers of galaxies is now much greater than the entropy free in the rest of the universe. Either mergers involved in forming supermassive black holes are rare,or the holes must be very efficient at capturing nearly all the entropy generated in the process. We argue that this information can be used to constrain supermassive black hole production, and may eventually provide a check on numerical results for mergers involving black holes.

gr-qc↗
arXiv2001

Non-associative Loops for Holger Bech Nielsen

Finite groups are of the greatest importance in science. Loops are a simple generalization of finite groups: they share all the group axioms except for the requirement that the binary operation be associative. The least loops that are not themselves groups are those of order five. We offer a brief discussion of these loops and challenge the reader (especially Holger) to find useful applications for them in physics.

hep-th↗
arXiv2001

Three Family N=1 SUSY Models from Z_n Orbifolded AdS/CFT

We present an analysis of compactifications of the type IIB superstring on AdS_5 x S^5 / Γ, where Γis an abelian cyclic group. Every Γ=Z_n of order n<= 12 is considered. This results in 60 chiral models, and a systematic analysis with n<8 yields four containing the minimal SUSY standard model with three families. One of these models extends to an infinite sequence of three-family MSSMs. We also give a lower bound on the number of chiral models for all values of n.

hep-ph↗
arXiv2001

Family Unification, Exotic States and Magnetic Monopoles

The embedding in SU(4)xSU(3)xSU(3) of the well studied gauge groups SU(4)xSU(2)xSU(2) and SU(3)xSU(3)xSU(3) naturally leads to family unification as opposed to simple family replication. An inescapable consequence is the predicted existence of (exotic)color singlet states that carry fractional electric charge. The corresponding magnetic monopoles carry multiple Dirac magnetic charge, can be relatively light (\sim 10^{7}-10^{13}GeV), and may be present in the galaxy not far below the Parker bound.

hep-ph↗
arXiv2001

Signature Studies of Cosmic Magnetic Monopoles

This talk explores the possibility that the Universe may be populated with relic magnetic monopoles. Observations of galactic and extragalactic magnetic fields, lead to the conclusion that monopoles of mass < 10^{14} GeV are accelerated in these fields to relativistic velocities. The relativistic monopole signatures and features we derive are (i) the protracted shower development, (ii) the Cherenkov signals, (iii) the tomography of the Earth with monopoles, and (iv) a model for monopole airshowers above the GZK cutoff.

astro-ph↗
arXiv2000

Classification of Conformality Models Based on Nonabelian Orbifolds

A systematic analysis is presented of compactifications of the IIB superstring on $AdS_5 \times S^5/Γ$ where $Γ$ is a non-abelian discrete group. Every possible $Γ$ with order $g \leq 31$ is considered. There exist 45 such groups but a majority cannot yield chiral fermions due to a certain theorem that is proved. The lowest order to embrace the nonSUSY standard $SU(3) \times SU(2) \times U(1)$ model with three chiral families is $Γ= D_4 \times Z_3$, with $g=24$; this is the only successful model found in the search. The consequent uniqueness of the successful model arises primarily from the scalar sector, prescribed by the construction, being sufficient to allow the correct symmetry breakdown.

hep-th↗
arXiv1999

The Ubiquitous Inflaton in String-Inspired Models

A string theory based inflationary model is developed where the inflaton interacts with a multitude of massive string level states causing dissipation of vacuum energy. Inflation terminates in a warm Universe without the need for reheating.

hep-ph↗
arXiv1999

The Interaction Structure and Cosmological Relevance of Mass Scales in String Motivated Supersymmetric Theories

A string motivated, N=1 global supersymmetric, general Lagrangian is obtained that represents an inflaton interacting with the modes of a string. Focus is placed on the Lagrangian's relevance to warm inflation, which is a cosmology based on dissipative dynamics. Several interaction schemes are identified from the general Lagrangian that may have interesting consequences for dissipative dynamics. Distributed-mass-models, which have been shown to solve the horizon problem within a warm inflation regime, are identified in the general Lagrangian.

hep-ph↗
arXiv1998

GUT Cosmic Magnetic Fields in a Warm Inflationary Universe

Sources of magnetic fields from grand unified theories are studied in the warm inflation regime. A ferromagnetic Savvidy vacuum scenario is presented that yields observationally interesting large scale magnetic fields. As an intermediate step, a general analysis is made of defect production at the onset of warm inflation and monopole constraints are obtained. Many features of this Savvidy vacuum scenario are applicable within a supercooled inflation regime and these points are discussed.

hep-ph↗
arXiv1997

$K_L \to π^o ν\barν$ in the Aspon Model

An attractive alternative to the standard model of CP violation is the aspon model. In this model, CP is spontaneously broken, automatically solving the strong CP problem. Recently, it has been shown that CP violation in the B system is much smaller in the aspon model than in the standard model. Here we provide a complementary study by considering $K_L\to π^oν\barν$, which is almost entirely CP violating and free of hadronic uncertainties, and show that the rate in the aspon model is many orders of magnitude below the standard model rate. Observation of $K_L\to π^oν\barν$ would rule out the aspon model.

hep-ph↗
arXiv1996

Representing Structural Information of Helical Charge Distributions in Cylindrical Coordinates

Structural information in the local electric field produced by helical charge distributions, such as dissolved DNA, is revealed in a straightforward manner employing cylindrical coordinates. Comparison of structure factors derived in terms of cylindrical and helical coordinates is made. A simple coordinate transformation serves to relate the Green function in cylindrical and helical coordinates. We also compare the electric field on the central axis of a single helix as calculated in both systems.

cond-mat↗
arXiv1996

Are we seeing magnetic monopole cosmic rays at $E\gsim 10^{20}$ eV?

We suggest that the highest energy $ \gsim 10^{20}$ eV cosmic ray primaries may be relativistic magnetic monopoles. Motivations for this hypothesis are twofold: (i) conventional primaries are problematic, while monopoles are naturally accelerated to $E \sim 10^{20}$ eV by galactic magnetic fields; (ii) the observed highest energy cosmic ray flux is just below the Parker limit for monopoles. By matching the cosmic monopole production mechanism to the observed highest energy cosmic ray flux we estimate the monopole mass to be $\lsim 10^{10}$ GeV.

astro-ph↗
arXiv1995

Constraining $α_s(M_Z)$ from the Hidden Sector

By including the effects of superstring thresholds, we reconsider minimal string unification together with the requirement of producing a supersymmetry-breaking gluino condensate in the hidden sector. This gives, for examples of phenomenologically-viable $Z_8'$ and other related orbifolds, the constraint that $0.1215 \leq α_s(M_Z) \leq 0.1270$. In such models, a hidden photino can be a source of cosmological dark matter detectable by gravitational microlensing.

hep-ph↗
arXiv1995

Magnetic Monopoles as the Highest Energy Cosmic Ray Primaries

We suggest that the highest energy $ \gsim 10^{20} eV$ cosmic ray primaries may be relativistic magnetic monopoles. Motivations for this hypothesis are that conventional primaries are problematic, while monopoles are naturally accelerated to $E \sim 10^{20} eV$ by galactic magnetic fields. By matching the cosmic monopole production mechanism to the observed highest energy cosmic ray flux we estimate the monopole mass to be $\sim 10^{10\pm1} GeV$.

astro-ph↗
arXiv1995

Topological Incarnations of Electroweak Defects

We propose a criterion to classify hybrid defects occurring in field theoretic models such as the standard electroweak model. This criterion leads us to consider the minimal extension of the electroweak model in which electroweak magnetic monopoles and $Z$-strings are topological. We briefly discuss the cosmology of such defects.

hep-ph↗
arXiv1995

Energy Density of Non-Minimally Coupled Scalar Field Cosmologies

Scalar fields coupled to gravity via $ξR Φ^2$ in arbitrary Friedmann-Robertson-Walker backgrounds can be represented by an effective flat space field theory. We derive an expression for the scalar energy density where the effective scalar mass becomes an explicit function of $ξ$ and the scale factor. The scalar quartic self-coupling gets shifted and can vanish for a particular choice of $ξ$. Gravitationally induced symmetry breaking and de-stabilization are possible in this theory.

gr-qc↗
arXiv1994

Minimal Family Unification

Absract It is proposed that there exist, within a new $SU(2)^{'}$, a gauged discrete group $Q_6$ (the order 12 double dihedral group) acting as a family symmetry. This nonabelian finite group can explain hierarchical features of families, using an assignment for quarks and leptons dictated by the requirements of anomaly cancellation and of no additional quarks.

hep-ph↗