2,159 research outputs found
Fermion Mass Hierarchy in Lifshitz Type Gauge Theory
We study the origin of fermion mass hierarchy and flavor mixing in a Lifshitz
type extension of the standard model including an extra scalar field. We show
that the hierarchical structure can originate from renormalizable interactions.
In contrast to the Froggatt-Nielsen mechanism, the higher the dimension of
associated operators, the heavier the fermion masses. Tiny masses for
left-handed neutrinos are obtained without introducing right-handed neutrinos.Comment: 13 pages; clarifications of some point
On the Definition of Decoherence
We examine the relationship between the decoherence of quantum-mechanical
histories of a closed system (as discussed by Gell-Mann and Hartle) and
environmentally-induced diagonalization of the density operator for an open
system. We study a definition of decoherence which incorporates both of these
ideas, and show that it leads to a consistent probabilistic interpretation of
the reduced density operator.Comment: 10 pages, LaTeX, SJSU/TP-93-1
Dirac neutrino mass from the beta decay end-point modified by the dynamics of a Lorentz-violating equation of motion
Using a generalized procedure for obtaining the equation of motion of a
propagating fermionic particle, we examine previous claims for a lightlike
preferred axis embedded in the framework of Lorentz-invariance violation with
preserved algebra. In a high energy scale, the corresponding equation of motion
is reduced to a conserving lepton number chiral (VSR) equation, and in a low
energy scale, the Dirac equation for a free is recovered. The new dynamics
introduces some novel ingredients (modified cross section) to the phenomenology
of the tritium beta decay end-point.Comment: 11 pages, 4 figure
Unification via intermediate symmetry breaking scales with the quartification gauge group
The idea of quark-lepton universality at high energies has been introduced as
a natural extension to the standard model. This is achieved by endowing leptons
with new degrees of freedom -- leptonic colour, an analogue of the familiar
quark colour. Grand and partially unified models which utilise this new gauge
symmetry SU(3)_\ell have been proposed in the context of the quartification
gauge group SU(3)^4. Phenomenologically successful gauge coupling constant
unification without supersymmetry has been demonstrated for cases where the
symmetry breaking leaves a residual SU(2)_\ell unbroken. Though attractive,
these schemes either incorporate ad hoc discrete symmetries and
non-renormalisable mass terms, or achieve only partial unification. We show
that grand unified models can be constructed where the quartification group can
be broken fully [i.e. no residual SU(2)_\ell] to the standard model gauge group
without requiring additional discrete symmetries or higher dimension operators.
These models also automatically have suppressed nonzero neutrino masses. We
perform a systematic analysis of the renormalisation-group equations for all
possible symmetry breaking routes from SU(3)^4 --> SU(3)_q x SU(2)_L x U(1)_Y.
This analysis indicates that gauge coupling unification can be achieved for
several different symmetry breaking patterns and we outline the requirements
that each gives on the unification scale. We also show that the unification
scenarios of those models which leave a residual SU(2)_\ell symmetry are not
unique. In both symmetry breaking cases, some of the scenarios require new
physics at the TeV scale, while others do not allow for new TeV phenomenology
in the fermionic sector.Comment: 25 page
Gapless Hartree-Fock Resummation Scheme for the O(N) Model
A modified selfconsistent Hartree-Fock approximation to the lambda*phi^4
theory with spontaneously broken O(N) symmetry is proposed. It preserves all
the desirable features, like conservation laws and thermodynamic consistency,
of the selfconsistent Dyson scheme generated from a 2PI functional, also known
as the Phi-derivable scheme, while simultaneously respecting the
Nambu-Goldstone theorem in the chiral-symmetry broken phase. Various
approximate resummation schemes are discussed.Comment: 13 pages, 10 figures / Version accepted by Phys. Rev. D: the
introduction has been expanded by a few remarks in order to further clarify
the goal of the pape
Decoherence of Hydrodynamic Histories: A Simple Spin Model
In the context of the decoherent histories approach to the quantum mechanics
of closed systems, Gell-Mann and Hartle have argued that the variables
typically characterizing the quasiclassical domain of a large complex system
are the integrals over small volumes of locally conserved densities --
hydrodynamic variables. The aim of this paper is to exhibit some simple models
in which approximate decoherence arises as a result of local conservation. We
derive a formula which shows the explicit connection between local conservation
and approximate decoherence. We then consider a class of models consisting of a
large number of weakly interacting components, in which the projections onto
local densities may be decomposed into projections onto one of two alternatives
of the individual components. The main example we consider is a one-dimensional
chain of locally coupled spins, and the projections are onto the total spin in
a subsection of the chain. We compute the decoherence functional for histories
of local densities, in the limit when the number of components is very large.
We find that decoherence requires two things: the smearing volumes must be
sufficiently large to ensure approximate conservation, and the local densities
must be partitioned into sufficiently large ranges to ensure protection against
quantum fluctuations.Comment: Standard TeX, 36 pages + 3 figures (postscript) Revised abstract and
introduction. To appear in Physical Review
Chiral symmetry patterns of excited mesons with the Coulomb-like linear confinement
The spectrum of mesons in a model where the only interaction is a
linear Coulomb-like instantaneous confining potential is studied. The
single-quark Green function as well as the dynamical chiral symmetry breaking
are obtained from the Schwinger-Dyson (gap) equation. Given the dressed quark
propagator, a complete spectrum of "usual" mesons is obtained from the
Bethe-Salpeter equation. The spectrum exhibits restoration of chiral and
symmetries at large spins and/or radial excitations. This property is
demonstrated both analytically and numerically. At large spins and/or radial
excitations higher degree of degeneracy is observed, namely all states with the
given spin fall into reducible representations that combine all possible chiral multiplets with the
given and . The structure of the meson wave functions as well as the
form of the angular and radial Regge trajectories are investigated.Comment: 1. Order of references has been changed and one reference has been
added; 2. A short discussion of nonrelativistic and semirelativistic quark
models has been added in the conclusion part on referee's request. To appear
in Phys. Rev.
Conservation Laws in the Quantum Mechanics of Closed Systems
We investigate conservation laws in the quantum mechanics of closed systems.
We review an argument showing that exact decoherence implies the exact
conservation of quantities that commute with the Hamiltonian including the
total energy and total electric charge. However, we also show that decoherence
severely limits the alternatives which can be included in sets of histories
which assess the conservation of these quantities when they are not coupled to
a long-range field arising from a fundamental symmetry principle. We then
examine the realistic cases of electric charge coupled to the electromagnetic
field and mass coupled to spacetime curvature and show that when alternative
values of charge and mass decohere, they always decohere exactly and are
exactly conserved as a consequence of their couplings to long-range fields.
Further, while decohering histories that describe fluctuations in total charge
and mass are also subject to the limitations mentioned above, we show that
these do not, in fact, restrict {\it physical} alternatives and are therefore
not really limitations at all.Comment: 22 pages, report UCSBTH-94-4, LA-UR-94-2101, CGPG-94/10-
Nonextensive diffusion as nonlinear response
The porous media equation has been proposed as a phenomenological
``non-extensive'' generalization of classical diffusion. Here, we show that a
very similar equation can be derived, in a systematic manner, for a classical
fluid by assuming nonlinear response, i.e. that the diffusive flux depends on
gradients of a power of the concentration. The present equation distinguishes
from the porous media equation in that it describes \emph{% generalized
classical} diffusion, i.e. with scaling, but with a generalized
Einstein relation, and with power-law probability distributions typical of
nonextensive statistical mechanics
Decoherence and classical predictability of phase space histories
We consider the decoherence of phase space histories in a class of quantum
Brownian motion models, consisting of a particle moving in a potential
in interaction with a heat bath at temperature and dissipation gamma, in
the Markovian regime. The evolution of the density operator for this open
system is thus described by a non-unitary master equation. The phase space
histories of the system are described by a class of quasiprojectors.
Generalizing earlier results of Hagedorn and Omn\`es, we show that a phase
space projector onto a phase space cell is approximately evolved under
the master equation into another phase space projector onto the classical
dissipative evolution of , and with a certain amount of degradation due
to the noise produced by the environment. We thus show that histories of phase
space samplings approximately decohere, and that the probabilities for these
histories are peaked about classical dissipative evolution, with a width of
peaking depending on the size of the noise.Comment: 34 pages, LATEX, revised version to avoid LATEX error
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