588 research outputs found
Heterotic Cosmic Strings
We show that all three conditions for the cosmological relevance of heterotic
cosmic strings, the right tension, stability and a production mechanism at the
end of inflation, can be met in the strongly coupled M-theory regime. Whereas
cosmic strings generated from weakly coupled heterotic strings have the well
known problems posed by Witten in 1985, we show that strings arising from
M5-branes wrapped around 4-cycles (divisors) of a Calabi-Yau in heterotic
M-theory compactifications, solve these problems in an elegant fashion.Comment: 25 pages, v2: section and references adde
Determining Heavy Mass Parameters in Supersymmetric SO(10) Models
Extrapolations of soft scalar mass parameters in supersymmetric theories can
be used to explore elements of the physics scenario near the grand unification
scale. We investigate the potential of this method in the lepton sector of
SO(10) which incorporates right-handed neutrino superfields. The method is
exemplified in two models by exploring limits on the precision that can be
expected from coherent LHC and e+e- collider analyses in the reconstruction of
the fundamental scalar mass parameters at the unification scale and of the
D-terms related to the breaking of grand unification symmetries. In addition,
the mass of the third-generation right-handed neutrino can be estimated in
seesaw scenarios. Even though the models are simplified and not intended to
account for all aspects of a final comprehensive SO(10) theory, they provide
nevertheless a valid base for identifying essential elements that can be
inferred on the fundamental high-scale theory from high-energy experiments.Comment: 26 pp LaTeX; version published in Phys. Rev.
Dark Matter from Baryon Asymmetry
The measured densities of dark and baryonic matter are surprisingly close to
each other, even though the baryon asymmetry and the dark matter are usually
explained by unrelated mechanisms. We consider a scenario where the dark matter
S is produced non-thermally from the decay of a messenger particle X, which
carries the baryon number and compensates for the baryon asymmetry in the
Universe, thereby establishing a connection between the baryonic and dark
matter densities. We propose a simple model to realize this scenario, adding
only a light singlet fermion S and a colored particle X which has a mass in the
O(TeV) range and a lifetime to appear long-lived in collider detector.
Therefore in hadron colliders the signal is similar to that of a stable or
long-lived gluino in supersymmetric models.Comment: 12 pages; v2: bounds on the mass of the messenger particle are
relaxed; conclusions unchanged. additional minor modification
Two-dimensional model of dynamical fermion mass generation in strongly coupled gauge theories
We generalize the Schwinger model on the lattice by adding a charged
scalar field. In this so-called model the scalar field shields
the fermion charge, and a neutral fermion, acquiring mass dynamically, is
present in the spectrum. We study numerically the mass of this fermion at
various large fixed values of the gauge coupling by varying the effective
four-fermion coupling, and find an indication that its scaling behavior is the
same as that of the fermion mass in the chiral Gross-Neveu model. This suggests
that the model is in the same universality class as the
Gross-Neveu model, and thus renormalizable and asymptotic free at arbitrary
strong gauge coupling.Comment: 18 pages, LaTeX2e, requires packages rotating.sty and curves.sty from
CTA
Aeration effects on water-structure impacts: Part 2. Wave impacts on a truncated vertical wall
Coisotropic D-branes on AdS4 x CP3 and massive deformations
We scan for massive type IIA SU(3)-structure compactifications of the type
AdS4 x CP3 with internal symmetry group SO(4). This group acts on CP3 with
cohomogeneity one, so that one would expect new non-homogeneous solutions. We
find however that all such solutions enhance their symmetry group to Sp(2) and
form, in fact, the homogeneous family first described in arXiv:0712.1396. This
is in accordance with arXiv:0901.0969, which argues from the CFT-side that
although new vacua with SO(4) symmetry group and N=2 supersymmetry should
exist, they fall outside our ansatz of strict SU(3)-structure, and instead have
genuine SU(3)x SU(3)-structure. We do find that the SO(4)-invariant
description, which singles out one preferential direction in the internal
space, is well-adapted for describing the embedding of AdS4-filling
supersymmetric D8-branes on both the original ABJM configuration as its massive
Sp(2)-symmetric deformations.Supersymmetry requires these D-branes to be of the
coisotropic type, which means in particular that their world-volume gauge field
must be non-trivial.Comment: 24 pages, 1 figure, v2: due to a serious mistake the claims of the
paper had to be correcte
Developmental transitions in body color in chacma baboon infants: Implications to estimate age and developmental pace
OBJECTIVES: In many primates, one of the most noticeable morphological developmental traits is the transition from natal fur and skin color to adult coloration. Studying the chronology and average age at such color transitions can be an easy and noninvasive method to (a) estimate the age of infants whose dates of birth were not observed, and (b) detect interindividual differences in the pace of development for infants with known birth dates. MATERIALS AND METHODS: Using a combination of photographs and field observations from 73 infant chacma baboons (Papio ursinus) of known ages, we (a) scored the skin color of six different body parts from pink to gray, as well as the color of the fur from black to gray; (b) validated our method of age estimation using photographic and field observations on an independent subset of 22 infants with known date of birth; and (c) investigated ecological, social, and individual determinants of age-related variation in skin and fur color. RESULTS: Our results show that transitions in skin color can be used to age infant chacma baboons less than 7 months old with accuracy (median number of days between actual and estimated age = 10, range = 0-86). We also reveal that food availability during the mother's pregnancy, but not during lactation, affects infant color-for-age and therefore acts as a predictor of developmental pace. DISCUSSION: This study highlights the potential of monitoring within- and between-infant variation in color to estimate age when age is unknown, and developmental pace when age is known
Diagnosing Spin at the LHC via Vector Boson Fusion
We propose a new technique for determining the spin of new massive particles
that might be discovered at the Large Hadron Collider. The method relies on
pair-production of the new particles in a kinematic regime where the vector
boson fusion production mechanism is enhanced. For this regime, we show that
the distribution of the leading jets as a function of their relative azimuthal
angle can be used to distinguish spin-0 from spin-1/2 particles. We illustrate
this effect by considering the particular cases of (i) strongly-interacting,
stable particles and (ii) supersymmetric particles carrying color charge. We
argue that this method should be applicable in a wide range of new physics
scenarios.Comment: 5 pages, 4 figure
Self-Breaking of the Standard Model Gauge Symmetry
If the gauge fields of the Standard Model propagate in TeV-size extra
dimensions, they rapidly become strongly coupled and can form scalar bound
states of quarks and leptons. If the quarks and leptons of the third generation
propagate in 6 or 8 dimensions, we argue that the most tightly bound scalar is
a composite of top quarks, having the quantum numbers of the Higgs doublet and
a large coupling to the top quark. In the case where the gauge bosons propagate
in a bulk of a certain volume, this composite Higgs doublet can successfully
trigger electroweak symmetry breaking. The mass of the top quark is correctly
predicted to within 20%, without the need to add a fundamental Yukawa
interaction, and the Higgs boson mass is predicted to lie in the range 165 -
230 GeV. In addition to the Higgs boson, there may be a few other scalar
composites sufficiently light to be observed at upcoming collider experiments.Comment: 26 pages, 4 figures, typos corrected, references adde
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