40,157 research outputs found
D Branes and Textures
We examine the flavor structure of the trilinear superpotential couplings
which can result from embedding the Standard Model within D brane sectors in
Type IIB orientifold models, which are examples within the Type I string
framework. We find in general that the allowed flavor structures of the Yukawa
coupling matrices to leading order are given by basic variations on the
"democratic" texture ansatz. In certain interesting cases, the Yukawa couplings
have a novel structure in which a single right-handed fermion couples
democratically at leading order to three left-handed fermions. We discuss the
viability of such a ``single right-handed democracy'' in detail; remarkably,
even though there are large mixing angles in the u,d sectors separately, the
CKM mixing angles are small. The analysis demonstrates the ways in which the
Type I superstring framework can provide a rich setting for investigating novel
resolutions to the flavor puzzle.Comment: 23 pages, references adde
LFV and Dipole Moments in Models with A4 Flavour Symmetry
It is presented an analysis on lepton flavour violating transitions, leptonic
magnetic dipole moments and electric dipole moments in a class of models
characterized by the flavour symmetry A4 x Z3 x U(1)_FN, whose choice is
motivated by the approximate Tri-Bimaximal mixing observed in neutrino
oscillations. A low-energy effective Lagrangian is constructed, where these
effects are dominated by dimension six operators, suppressed by the scale M of
new physics. All the flavour breaking effects are universally described by the
vacuum expectation values of a set of spurions. Two separate cases, a
supersymmetric and a general one, are described. An upper limit on the reactor
angle of a few percent is concluded.Comment: 10 pages, 1 figure. Adapted from a talk given at "DISCRETE'08:
Symposium on Prospects in the Physics of Discrete Symmetries", December 11-16
2008, Valencia, Spai
Recurrence Formulas for Fully Exponentially Correlated Four-Body Wavefunctions
Formulas are presented for the recursive generation of four-body integrals in
which the integrand consists of arbitrary integer powers (>= -1) of all the
interparticle distances r_ij, multiplied by an exponential containing an
arbitrary linear combination of all the r_ij. These integrals are
generalizations of those encountered using Hylleraas basis functions, and
include all that are needed to make energy computations on the Li atom and
other four-body systems with a fully exponentially correlated Slater-type basis
of arbitrary quantum numbers. The only quantities needed to start the recursion
are the basic four-body integral first evaluated by Fromm and Hill, plus some
easily evaluated three-body "boundary" integrals. The computational labor in
constructing integral sets for practical computations is less than when the
integrals are generated using explicit formulas obtained by differentiating the
basic integral with respect to its parameters. Computations are facilitated by
using a symbolic algebra program (MAPLE) to compute array index pointers and
present syntactically correct FORTRAN source code as output; in this way it is
possible to obtain error-free high-speed evaluations with minimal effort. The
work can be checked by verifying sum rules the integrals must satisfy.Comment: 10 pages, no figures, accepted by Phys. Rev. A (January 2009
Entangled inputs cannot make imperfect quantum channels perfect
Entangled inputs can enhance the capacity of quantum channels, this being one
of the consequences of the celebrated result showing the non-additivity of
several quantities relevant for quantum information science. In this work, we
answer the converse question (whether entangled inputs can ever render noisy
quantum channels have maximum capacity) to the negative: No sophisticated
entangled input of any quantum channel can ever enhance the capacity to the
maximum possible value; a result that holds true for all channels both for the
classical as well as the quantum capacity. This result can hence be seen as a
bound as to how "non-additive quantum information can be". As a main result, we
find first practical and remarkably simple computable single-shot bounds to
capacities, related to entanglement measures. As examples, we discuss the qubit
amplitude damping and identify the first meaningful bound for its classical
capacity.Comment: 5 pages, 2 figures, an error in the argument on the quantum capacity
corrected, version to be published in the Physical Review Letter
Recursion relations for Hylleraas three-electron integral
Recursion relations for Hylleraas three-electron integral are obtained in a
closed form by using integration by parts identities. Numerically fast and well
stable algorithm for the calculation of the integral with high powers of
inter-electronic coordinates is presented.Comment: 12 pages, requires RevTeX4, submitted to Phys. Rev.
Trimaximal neutrino mixing from vacuum alignment in A4 and S4 models
Recent T2K results indicate a sizeable reactor angle theta_13 which would
rule out exact tri-bimaximal lepton mixing. We study the vacuum alignment of
the Altarelli-Feruglio A4 family symmetry model including additional flavons in
the 1' and 1" representations and show that it leads to trimaximal mixing in
which the second column of the lepton mixing matrix consists of the column
vector (1,1,1)^T/sqrt{3}, with a potentially large reactor angle. In order to
limit the reactor angle and control the higher order corrections, we propose a
renormalisable S4 model in which the 1' and 1" flavons of A4 are unified into a
doublet of S4 which is spontaneously broken to A4 by a flavon which enters the
neutrino sector at higher order. We study the vacuum alignment in the S4 model
and show that it predicts accurate trimaximal mixing with approximate
tri-bimaximal mixing, leading to a new mixing sum rule testable in future
neutrino experiments. Both A4 and S4 models preserve form dominance and hence
predict zero leptogenesis, up to renormalisation group corrections.Comment: 24 pages, 2 figures, version to be published in JHE
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