2,038 research outputs found
A D-moduli problem?
We point out a generic problem in string-inspired supergravity models with an
anomalous . A large number of matter multiplets charged under
remain massless above the supersymmetry-breaking scale because of degeneracy of
vacua solving the D-flatness conditions. A toy model is analyzed as an
illustration of the mechanism; we find the surprising result that many scalars
remain massless after supersymmetry-breaking in a hidden sector.Comment: 11 pages, full postscript also available from
http://phyweb.lbl.gov/theorygroup/papers/44856.p
D-brane Inspired Fermion Mass Textures
In this paper, the issues of the quark mass hierarchies and the Cabbibo
Kobayashi Maskawa mixing are analyzed in a class of intersecting D-brane
configurations with Standard Model gauge symmetry. The relevant mass matrices
are constructed taking into account the constraints imposed by extra abelian
symmetries and anomaly cancelation conditions. Possible mass generating
mechanisms including perturbative as well as non-perturbative effects are
discussed and specific patterns of mass textures are found characterized by the
hierarchies of the scales where the various sources contribute. It is argued
that the Cholesky decomposition of the mass matrices is the most appropriate
way to determine the properties of these fermion mass patterns, while the
associated triangular mass matrix form provides a unified description of all
phenomenologically equivalent symmetric and non-symmetric mass matrices. An
elegant analytic formula is derived for the Cholesky triangular form of the
mass matrices where the entries are given as simple functions of the mass
eigenstates and the diagonalizing transformation entries. Finally, motivated by
the possibility of vanishing zero Yukawa mass entries in several D-brane and
F-theory constructions due to the geometry of the internal space, we analyse in
detail all possible texture-zeroes mass matrices within the proposed new
context. These new texture-zeroes are compared to those existing in the
literature while D-brane inspired cases are worked out in detail.Comment: 58 pages, 7 figure
Analysis of Running Coupling Constant Unification in String Theory
We use recently obtained 2-loop string coupling constants to analyze a class
of string models based on orbifold compactification. Assuming weak coupling at
the string scale and single-scale unification leads to restrictions on the
spectrum of massive (between the string scale and the weak scale) matter
supermultiplets and/or on the Kac-Moody algebra level.Comment: 12 page
A Model of Yukawa Hierarchies
We present a model for the observed hierarchies among the Yukawa couplings of
the standard model in the context of an effective low energy theory with an
anomalous U(1) symmetry. This symmetry, a generic feature of superstring
compactification, is a remnant of the Green-Schwarz anomaly cancellation
mechanism. The gauge group is that of the standard model, augmented by X, the
anomalous U(1), and two family-dependent phase symmetries and
. The correct hierarchies are reproduced only when
at the cut-off. To cancel anomalies, right-handed neutrinos and other standard
model singlets must be introduced. Independently of the charges of the
right-handed neutrinos, this model produces the same neutrino mixing matrix and
an inverted hierarchy of neutrino masses. The heaviest is the electron neutrino
with a mass meV, and mixing of the order of with each of
the other two neutrinos.Comment: 15 pages, no figures, LaTex. Revised version, containing minor
typographical corrections, as well as a substantial revision of the final
three paragraphs of the text. Submitted to Physics Letters
Gauging Away the Strong CP Problem
We propose a new solution to the strong-CP problem. It involves the existence
of an unbroken gauged symmetry whose gauge boson gets a Stuckelberg
mass term by combining with a pseudoscalar field . The latter has
axion-like couplings to so that the theta parameter may
be gauged away by a gauge transformation. This system leads to mixed
gauge anomalies and we argue that they are cancelled by the addition of an
appropriate Wess-Zumino term, so that no SM fermions need to be charged under
. We discuss scenarios in which the above set of fields and couplings
appear. The mechanism is quite generic, but a natural possibility is that the
the symmetry arises from bulk gauge bosons in theories with extra
dimensions or string models. We show that in certain D-brane Type-II string
models (with antisymmetric tensor field strength fluxes) higher dimensional
Chern-Simons couplings give rise to the required D=4 Wess-Zumino terms upon
compactification. In one of the possible string realizations of the mechanism
the gauge boson comes from the Kaluza-Klein reduction of the
eleven-dimensional metric in M-theory.Comment: 21 pages, latex, one eps figure; v2 improved discussio
A Classification of 3-Family Grand Unification in String Theory I. The SO(10) and E_6 Models
We give a classification of 3-family SO(10) and E_6 grand unification in
string theory within the framework of conformal field theory and asymmetric
orbifolds. We argue that the construction of such models in the heterotic
string theory requires certain Z_6 asymmetric orbifolds that include a Z_3
outer-automorphism, the latter yielding a level-3 current algebra for the grand
unification gauge group SO(10) or E_6. We then classify all such Z_6 asymmetric
orbifolds that result in models with a non-abelian hidden sector. All models
classified in this paper have only one adjoint (but no other higher
representation) Higgs field in the grand unified gauge group. In addition, all
of them are completely anomaly free. There are two types of such 3-family
models. The first type consists of the unique SO(10) model with SU(2) X SU(2) X
SU(2) as its hidden sector (which is not asymptotically-free at the string
scale). This SO(10) model has 4 left-handed and 1 right-handed 16s. The second
type is described by a moduli space containing 17 models (distinguished by
their massless spectra). All these models have an SU(2) hidden sector, and 5
left-handed and 2 right-handed families in the grand unified gauge group. One
of these models is the unique E_6 model with an asymptotically-free SU(2)
hidden sector. The others are SO(10) models, 8 of them with an asymptotically
free hidden sector at the string scale.Comment: 35 pages, Revtex 3.0, one eps figure (to appear in Phys. Rev. D
A new scenario for string unification
We present a new scenario for gauge coupling unification in flipped SU(5)
string models, which identifies the scale of SU(3) and SU(2)
unification with the empirical ~GeV scale, and the
scale of SU(5) and U(1) unification with the theoretical ~GeV string unification scale. The vacuum shift
necessary for the cancellation of the anomalous and an SU(4)
hidden sector with fractionally-charged particles, play a crucial role in the
dynamical determination of all intermediate mass scales in this scenario.Comment: 8 pages, LaTeX, 2 figures (uuencoded
Basketball game-related statistics that discriminate between teams season-long success
The aim of the present study was to identify the game-related statistics that discriminate between season-long successful and unsuccessful basketball teams participating in the Spanish Basketball League (LEB1). The sample included all 145 average records per season from the 870 games played between the 2000-2001 and the 2005-2006 regular seasons. The following game-related statistics were gathered from the official box scores of the Spanish Basketball Federation: 2- and 3-point field-goal attempts (both successful and unsuccessful), free-throws (both successful and unsuccessful), defensive and offensive rebounds, assists, steals, turnovers, blocks (both made and received), and fouls (both committed and received). To control for season variability, all results were normalized to minutes played each season and then converted to z-scores. The results allowed discrimination between best and worst teams' performances through the following game-related statistics: assists (SC=0.47), steals (SC=0.34), and blocks (SC=0.30). The function obtained correctly classified 82.4% of the cases. In conclusion, season-long performance may be supported by players' and teams' passing skills and defensive preparation
Neutrino Masses, Baryon Asymmetry, Dark Matter and the Moduli Problem : A Complete Framework
Recent developments in string theory have led to "realistic" string
compactifications which lead to moduli stabilization while generating a
hierarchy between the Electroweak and Planck scales at the same time. However,
this seems to suggest a rethink of our standard notions of cosmological
evolution after the end of inflation and before the beginning of BBN. We argue
that within classes of realistic string compactifications, there generically
exists a light modulus with a mass comparable to that of the gravitino which
generates a large late-time entropy when it decays. Therefore, all known
mechanisms of generating the baryon asymmetry of the Universe in the literature
have to take this fact into account. In this work, we find that it is still
possible to naturally generate the observed baryon asymmetry of the Universe as
well as light left-handed neutrino masses from a period of Affleck-Dine(AD)
leptogenesis shortly after the end of inflation, in classes of realistic string
constructions with a minimal extension of the MSSM below the unification scale
(consisting only of right-handed neutrinos) and satisfying certain microscopic
criteria described in the text. The consequences are as follows. The lightest
left-handed neutrino is required to be virtually massless. The moduli
(gravitino) problem can be naturally solved in this framework both within
gravity and gauge mediation. The observed upper bound on the relic abundance
constrains the moduli-matter and moduli-gravitino couplings since the DM is
produced non-thermally within this framework. Finally, although not a definite
prediction, the framework naturally allows a light right-handed neutrino and
sneutrinos around the electroweak scale which could have important implications
for DM as well as the LHC.Comment: 41 pages, no figures, journal version adde
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