120 research outputs found
The stability of the O(N) invariant fixed point in three dimensions
We study the stability of the O(N) fixed point in three dimensions under
perturbations of the cubic type. We address this problem in the three cases
by using finite size scaling techniques and high precision Monte
Carlo simulations. It is well know that there is a critical value
below which the O(N) fixed point is stable and above which the cubic fixed
point becomes the stable one. While we cannot exclude that , as recently
claimed by Kleinert and collaborators, our analysis strongly suggests that
coincides with 3.Comment: latex file of 18 pages plus three ps figure
Neutrino masses in the Lepton Number Violating MSSM
We consider the most general supersymmetric model with minimal particle
content and an additional discrete Z_3 symmetry (instead of R-parity), which
allows lepton number violating terms and results in non-zero Majorana neutrino
masses. We investigate whether the currently measured values for lepton masses
and mixing can be reproduced. We set up a framework in which Lagrangian
parameters can be initialised without recourse to assumptions concerning
trilinear or bilinear superpotential terms, CP-conservation or
intergenerational mixing and analyse in detail the one loop corrections to the
neutrino masses. We present scenarios in which the experimental data are
reproduced and show the effect varying lepton number violating couplings has on
the predicted atmospheric and solar mass^2 differences. We find that with
bilinear lepton number violating couplings in the superpotential of the order 1
MeV the atmospheric mass scale can be reproduced. Certain trilinear
superpotential couplings, usually, of the order of the electron Yukawa coupling
can give rise to either atmospheric or solar mass scales and bilinear
supersymmetry breaking terms of the order 0.1 GeV^2 can set the solar mass
scale. Further details of our calculation, Lagrangian, Feynman rules and
relevant generic loop diagrams, are presented in three Appendices.Comment: 48 pages, 7 figures, v2 references added, typos corrected, published
versio
Higgs mediated Double Flavor Violating top decays in Effective Theories
The possibility of detecting double flavor violating top quark transitions at
future colliders is explored in a model-independent manner using the effective
Lagrangian approach through the () decays. A
Yukawa sector that contemplates invariants of up to
dimension six is proposed and used to derive the most general flavor violating
and CP violating and vertices of renormalizable type.
Low-energy data, on high precision measurements, and experimental limits are
used to constraint the and vertices and then used to
predict the branching ratios for the decays. It is found
that this branching ratios may be of the order of , for a
relative light Higgs boson with mass lower than , which could be more
important than those typical values found in theories beyond the standard model
for the rare top quark decays () or . %% LHC experiments, by using a total integrated luminosity of of data, will be able to rule out, at 95% C.L., DFV top quark
decays up to a Higgs mass of 155 GeV/ or discover such a process up to a
Higgs mass of 147 GeV/.Comment: 24 pages, 11 figure
Quantum group symmetry of the Quantum Hall effect on the non-flat surfaces
After showing that the magnetic translation operators are not the symmetries
of the QHE on non-flat surfaces , we show that there exist another set of
operators which leads to the quantum group symmetries for some of these
surfaces . As a first example we show that the symmetry of the QHE on
sphere leads to algebra in the equator . We explain this result by a
contraction of . Secondly , with the help of the symmetry operators of
QHE on the Pioncare upper half plane , we will show that the ground state wave
functions form a representation of the algebra .Comment: 8 pages,latex,no figur
CPT and Other Symmetries in String/M Theory
We initiate a search for non-perturbative consistency conditions in M theory.
Some non-perturbative conditions are already known in Type I theories; we
review these and search for others. We focus principally on possible anomalies
in discrete symmetries. It is generally believed that discrete symmetries in
string theories are gauge symmetries, so anomalies would provide evidence for
inconsistencies. Using the orbifold cosmic string construction, we give some
evidence that the symmetries we study are gauged. We then search for anomalies
in discrete symmetries in a variety of models, both with and without
supersymmetry. In symmetric orbifold models we extend previous searches, and
show in a variety of examples that all anomalies may be canceled by a
Green-Schwarz mechanism. We explore some asymmetric orbifold constructions and
again find that all anomalies may be canceled this way. Then we turn to Type
IIB orientifold models where it is known that even perturbative anomalies are
non-universal. In the examples we study, by combining geometric discrete
symmetries with continuous gauge symmetries, one may define non-anomalous
discrete symmetries already in perturbation theory; in other cases, the
anomalies are universal. Finally, we turn to the question of CPT conservation
in string/M theory. It is well known that CPT is conserved in all string
perturbation expansions; here in a number of examples for which a
non-perturbative formulation is available we provide evidence that it is
conserved exactly.Comment: 52 pages.1 paragraph added in introduction to clarify assumption
A model realizing the Harrison-Perkins-Scott lepton mixing matrix
We present a supersymmetric model in which the lepton mixing matrix
obeys, at the seesaw scale, the Harrison--Perkins--Scott
\textit{Ansatz}--vanishing , maximal atmospheric neutrino mixing, and
( is the solar mixing angle). The
model features a permutation symmetry among the three lepton multiplets
of each type--left-handed doublets, right-handed charged leptons, and
right-handed neutrinos--and among three Higgs doublets and three
zero-hypercharge scalar singlets; a fourth right-handed neutrino, a fourth
Higgs doublet, and a fourth scalar singlet are invariant under . In
addition, the model has seven \mathbbm{Z}_2 symmetries, out of which six do
not commute with . Supersymmetry is needed in order to eliminate some
quartic terms from the scalar potential, quartic terms which would make
impossible to obtain the required vacuum expectation values of the three Higgs
doublets and three scalar singlets. The Yukawa couplings to the charged leptons
are flavour diagonal, so that flavour-changing neutral Yukawa interactions only
arise at loop level.Comment: 16 pages, plain LaTeX, no figures; some clarifying remarks in the
conclusions and references added, version accepted for publication in JHE
q-Quaternions and q-deformed su(2) instantons
We construct (anti)instanton solutions of a would-be q-deformed su(2)
Yang-Mills theory on the quantum Euclidean space R_q^4 [the SO_q(4)-covariant
noncommutative space] by reinterpreting the function algebra on the latter as a
q-quaternion bialgebra. Since the (anti)selfduality equations are covariant
under the quantum group of deformed rotations, translations and scale change,
by applying the latter we can generate new solutions from the one centered at
the origin and with unit size. We also construct multi-instanton solutions. As
they depend on noncommuting parameters playing the roles of `sizes' and
`coordinates of the centers' of the instantons, this indicates that the moduli
space of a complete theory will be a noncommutative manifold. Similarly, gauge
transformations should be allowed to depend on additional noncommutative
parameters.Comment: Latex file, 39 pages. Final version appeared in JM
Ground state cooling in a bad cavity
We study the mechanical effects of light on an atom trapped in a harmonic
potential when an atomic dipole transition is driven by a laser and it is
strongly coupled to a mode of an optical resonator. We investigate the cooling
dynamics in the bad cavity limit, focussing on the case in which the effective
transition linewidth is smaller than the trap frequency, hence when sideband
cooling could be implemented. We show that quantum correlations between the
mechanical actions of laser and cavity field can lead to an enhancement of the
cooling efficiency with respect to sideband cooling. Such interference effects
are found when the resonator losses prevail over spontaneous decay and over the
rates of the coherent processes characterizing the dynamics.Comment: 6 pages, 5 figures; J. Mod. Opt. (2007
Characterisations of Classical and Non-classical states of Quantised Radiation
A new operator based condition for distinguishing classical from
non-classical states of quantised radiation is developed. It exploits the fact
that the normal ordering rule of correspondence to go from classical to quantum
dynamical variables does not in general maintain positivity. It is shown that
the approach naturally leads to distinguishing several layers of increasing
nonclassicality, with more layers as the number of modes increases. A
generalisation of the notion of subpoissonian statistics for two-mode radiation
fields is achieved by analysing completely all correlations and fluctuations in
quadratic combinations of mode annihilation and creation operators conserving
the total photon number. This generalisation is nontrivial and intrinsically
two-mode as it goes beyond all possible single mode projections of the two-mode
field. The nonclassicality of pair coherent states, squeezed vacuum and
squeezed thermal states is analysed and contrasted with one another, comparing
the generalised subpoissonian statistics with extant signatures of nonclassical
behaviour.Comment: 16 pages, Revtex, One postscript Figure compressed and uuencoded
Replaced, minor changes in eq 4.30 and 4.32. no effect on the result
A tentative Replica Study of the Glass Transition
We propose a method to study quantitatively the glass transition in a system
of interacting particles. In spite of the absence of any quenched disorder, we
introduce a replicated version of the hypernetted chain equations. The solution
of these equations, for hard or soft spheres, signals a transition to the glass
phase. However the predicted value of the energy and specific heat in the glass
phase are wrong, calling for an improvement of this method.Comment: 9 pages, four postcript figures attache
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