3,790 research outputs found
Low-energy sector of 8-dimensional General Relativity: Electro-Weak model and neutrino mass
In a Kaluza-Klein space-time , we demonstrate that the
dimensional reduction of spinors provides a 4-field, whose associated SU(2)
gauge connections are geometrized. However, additional and gauge-violating
terms arise, but they are highly suppressed by a factor , which fixes
the amount of the spinor dependence on extra-coordinates. The application of
this framework to the Electro-Weak model is performed, thus giving a lower
bound for from the request of the electric charge conservation.
Moreover, we emphasize that also the Higgs sector can be reproduced, but
neutrino masses are predicted and the fine-tuning on the Higgs parameters can
be explained, too.Comment: 14 pages, 1 figure, to appear on Int. J. Mod. Phys.
Magnetic catalysis in the (2+1)-dimensional Gross-Neveu model
We study the Gross-Neveu model in dimensions in an external magnetic
field . We first summarize known mean-field results, obtained in the limit
of large flavor number , before presenting lattice results using
the overlap discretization to study one reducible fermion flavor,
. Our findings indicate that the magnetic catalysis phenomenon,
i.e., an increase of the chiral condensate with the magnetic field, persists
beyond the mean-field limit for temperatures below the chiral phase transition
and that the critical temperature grows with increasing magnetic field. This is
in contrast to the situation in QCD, where the broken phase shrinks with
increasing while the condensate exhibits a non-monotonic -dependence
close to the chiral crossover, and we comment on this discrepancy. We do not
find any trace of inhomogeneous phases induced by the magnetic field.Comment: 10 pages + 4 pages appendix, 10 figure
Fermion Dynamics by Internal and Space-Time Symmetries
This manuscript is devoted to introduce a gauge theory of the Lorentz Group
based on the ambiguity emerging in dealing with isometric
diffeo-morphism-induced Lorentz transformations. The behaviors under local
transformations of fermion fields and spin connections (assumed to be ordinary
world vectors) are analyzed in flat space-time and the role of the torsion
field, within the generalization to curved space-time, is briefly discussed.
The fermion dynamics is then analyzed including the new gauge fields and
assuming time-gauge. Stationary solutions of the problem are also analyzed in
the non-relativistic limit, to study the spinor structure of an hydrogen-like
atom.Comment: 10 pages, no figur
Decay of accelerated particles
We study how the decay properties of particles are changed by acceleration.
It is shown that under the influence of acceleration (1) the lifetime of
particles is modified and (2) new processes (like the decay of the proton)
become possible. This is illustrated by considering scalar models for the decay
of muons, pions, and protons. We discuss the close conceptual relation between
these processes and the Unruh effect.Comment: Latex2e, 12 pages, 6 Postscript figures included with epsfig, to
appear in Phys. Rev.
A description of the f2(1270), rho3(1690), f4(2050), rho5(2350) and f6(2510) resonances as multi-rho(770) states
In a previous work regarding the interaction of two resonances,
the () resonance was obtained dynamically as a
two- molecule with a very strong binding energy, 135~MeV per
particle. In the present work we use the interaction in spin 2 and
isospin 0 channel to show that the resonances (),
(), () and ()
are basically molecules of increasing number of particles. We use
the fixed center approximation of the Faddeev equations to write the multi-body
interaction in terms of the two-body scattering amplitudes. We find the masses
of the states very close to the experimental values and we get an increasing
value of the binding energy per as the number of mesons is
increased.Comment: 17 pages, 6 figure
Generating functional for the gravitational field: implementation of an evolutionary quantum dynamics
We provide a generating functional for the gravitational field, associated to
the relaxation of the primary constraints as extended to the quantum sector.
This requirement of the theory, relies on the assumption that a suitable time
variable exist, when taking the T-products of the dynamical variables. More
precisely, we start from the gravitational field equations written in the
Hamiltonian formalism and expressed via Misner-like variables; hence we
construct the equation to which the T-products of the dynamical variables obey
and transform this paradigm in terms of the generating functional, as taken on
the theory phase-space. We show how the relaxation of the primary constraints
(which correspond to break down the invariance of the quantum theory under the
4-diffeomorphisms) is summarized by a free functional taken on the Lagrangian
multipliers, accounting for such constraints in the classical theory. The issue
of our analysis is equivalent to a Gupta-Bleuler approach on the quantum
implementation of all the gravitational constraints; in fact, in the limit of
small , the quantum dynamics is described by a Schr\"odinger equation,
as soon as the mean values of the momenta, associated to the lapse function and
the shift vector, are not vanishing. Finally we show how, in the classical
limit, the evolutionary quantum gravity reduces to General Relativity in the
presence of an Eckart fluid, which corresponds to the classical counterpart of
the physical clock, introduced in the quantum theory.Comment: 23 pages, no figures, to appear on International Journal of Modern
Physics
Two-electron atoms, ions and molecules
The quantum mechanics of two-electron systems is reviewed, starting with the
ground state of the helium atom and helium-like ions, with central charge . For Z=1, demonstrating the stability of the negative hydrogen ion, H,
cannot be achieved using a mere product of individual electron wave functions,
and requires instead an explicit account for the anticorrelation among the two
electrons. The wave function proposed by Chandrasekhar is revisited, where the
permutation symmetry is first broken and then restored by a counter-term. More
delicate problems can be studied using the same strategy: the stability of
hydrogen-like ions for any value of the proton-to-electron mass
ratio ; the energy of the lowest spin-triplet state of helium and
helium-like ions; the stability of the doubly-excited hydrogen ion with
unnatural parity. The positronium molecule , which has been
predicted years ago and discovered recently, can also be shown to be stable
against spontaneous dissociation, though the calculation is a little more
involved. Emphasis is put on symmetry breaking which can either spoil or
improve the stability of systems.Comment: 16 pages, 2 figure
Non-Markovian entanglement dynamics of quantum continuous variable systems in thermal environments
We study two continuous variable systems (or two harmonic oscillators) and
investigate their entanglement evolution under the influence of non-Markovian
thermal environments. The continuous variable systems could be two modes of
electromagnetic fields or two nanomechanical oscillators in the quantum domain.
We use quantum open system method to derive the non-Markovian master equations
of the reduced density matrix for two different but related models of the
continuous variable systems. The two models both consist of two interacting
harmonic oscillators. In model A, each of the two oscillators is coupled to its
own independent thermal reservoir, while in model B the two oscillators are
coupled to a common reservoir. To quantify the degrees of entanglement for the
bipartite continuous variable systems in Gaussian states, logarithmic
negativity is used. We find that the dynamics of the quantum entanglement is
sensitive to the initial states, the oscillator-oscillator interaction, the
oscillator-environment interaction and the coupling to a common bath or to
different, independent baths.Comment: 10 two-column pages, 8 figures, to appear in Phys. Rev.
Non-Markovian dynamics of a nanomechanical resonator measured by a quantum point contact
We study the dynamics of a nanomechanical resonator (NMR) subject to a
measurement by a low transparency quantum point contact (QPC) or tunnel
junction in the non-Markovian domain. We derive the non-Markovian
number-resolved (conditional) and unconditional master equations valid to
second order in the tunneling Hamiltonian without making the rotating-wave
approximation and the Markovian approximation, generally made for systems in
quantum optics. Our non-Markovian master equation reduces, in appropriate
limits, to various Markovian versions of master equations in the literature. We
find considerable difference in dynamics between the non-Markovian cases and
its Markovian counterparts. We also calculate the time-dependent transport
current through the QPC which contains information about the measured NMR
system. We find an extra transient current term proportional to the expectation
value of the symmetrized product of the position and momentum operators of the
NMR. This extra current term, with a coefficient coming from the combination of
the imaginary parts of the QPC reservoir correlation functions, has a
substantial contribution to the total transient current in the non-Markovian
case, but was generally ignored in the studies of the same problem in the
literature. Considering the contribution of this extra term, we show that a
significantly qualitative and quantitative difference in the total transient
current between the non-Markovian and the Markovian wide-band-limit cases can
be observed. Thus, it may serve as a witness or signature of the non-Markovian
features in the coupled NMR-QPC system.Comment: Accepted for publication in Physical Review B (20 pages, 13 figures
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