3,095 research outputs found
Flavordynamics with Conformal Matter and Gauge Theories on Compact Hyperbolic Manifolds in Extra Dimensions
We outline a toy model in which a unique mechanism may trigger a dynamical
chain resulting in key low-energy regularities. The starting points are a
negative cosmological term in the bulk and conformally invariant nongravity
sector. These elements ensure compactification of the extra dimensional space
on a compact hyperbolic manifold (with the negative and constant scalar
curvature). The overall geometry is then M_4 x B_n. The negative curvature on
B_n triggers the formation of the four-dimensional defect which provides in
turn a dynamical localization of ordinary particles. It also leads,
simultaneously, to a spontaneous breaking of gauge symmetry through a Higgs
mechanism. Masses of the fermions, gauge bosons and scalars all derive from the
curvature of the internal manifold such that the Higgs boson is generally
heavier than the gauge bosons. The factorizable geometry M_4 x B_n and flatness
of M_4 require fine-tuning.Comment: 16 pp, added references and a figure with improvements in text;
journal versio
Sensorimotor coordination and metastability in a situated HKB model
Oscillatory phenomena are ubiquitous in nature and have become particularly relevant for the study of brain and behaviour. One of the simplest, yet explanatorily powerful, models of oscillatory Coordination Dynamics is the HakenâKelsoâBunz (HKB) model. The metastable regime described by the HKB equation has been hypothesised to be the signature of brain oscillatory dynamics underlying sensorimotor coordination. Despite evidence supporting such a hypothesis, to our knowledge, there are still very few models (if any) where the HKB equation generates spatially situated behaviour and, at the same time, has its dynamics modulated by the behaviour it generates (by means of the sensory feedback resulting from body movement). This work presents a computational model where the HKB equation controls an agent performing a simple gradient climbing task and shows (i) how different metastable dynamical patterns in the HKB equation are generated and sustained by the continuous interaction between the agent and its environment; and (ii) how the emergence of functional metastable patterns in the HKB equation â i.e. patterns that generate gradient climbing behaviour â depends not only on the structure of the agent's sensory input but also on the coordinated coupling of the agent's motorâsensory dynamics. This work contributes to Kelso's theoretical framework and also to the understanding of neural oscillations and sensorimotor coordination
Flux Compactifications on Calabi-Yau Threefolds
The presence of RR and NS three-form fluxes in type IIB string
compactification on a Calabi-Yau orientifold gives rise to a nontrivial
superpotential W for the dilaton and complex structure moduli. This
superpotential is computable in terms of the period integrals of the Calabi-Yau
manifold. In this paper, we present explicit examples of both supersymmetric
and nonsupersymmetric solutions to the resulting 4d N=1 supersymmetric no-scale
supergravity, including some nonsupersymmetric solutions with relatively small
values of W. Our examples arise on orientifolds of the hypersurfaces in
and . They serve as explicit
illustrations of several of the ingredients which have played a role in the
recent proposals for constructing de Sitter vacua of string theory.Comment: 30 pages, harvmac big; refs and minor comments adde
Exploration and stabilization of Ras1 mating zone: A mechanism with positive and negative feedbacks.
In mating fission yeast cells, sensing and response to extracellular pheromone concentrations occurs through an exploratory Cdc42 patch that stochastically samples the cell cortex before stabilizing towards a mating partner. Active Ras1 (Ras1-GTP), an upstream regulator of Cdc42, and Gap1, the GTPase-activating protein for Ras1, localize at the patch. We developed a reaction-diffusion model of Ras1 patch appearance and disappearance with a positive feedback by a Guanine nucleotide Exchange Factor (GEF) and Gap1 inhibition. The model is based on new estimates of Ras1-GDP, Ras1-GTP and Gap1 diffusion coefficients and rates of cytoplasmic exchange studied by FRAP. The model reproduces exploratory patch behavior and lack of Ras1 patch in cells lacking Gap1. Transition to a stable patch can occur by change of Gap1 rates constants or local increase of the positive feedback rate constants. The model predicts that the patch size and number of patches depend on the strength of positive and negative feedbacks. Measurements of Ras1 patch size and number in cells overexpressing the Ras1 GEF or Gap1 are consistent with the model
Breaking Electroweak Symmetry Strongly
The problem of electroweak symmetry breaking is reviewed with discussion of
future relevant experimentation at LHC and linear colliders. The
possibility of strong electroweak symmetry breaking is examined in more detail,
using the BESS (Breaking Electroweak Symmetry Strongly) model as a basis for
the discussion. The formal constructions are briefly presented and the possible
expectations at future colliders are summarized.Comment: 20 pages, LaTeX, UGVA-DPT 1994/04-846. To appear in the Memorial
Volume for Professor Robert Marshak, edited by E.C.G. Sudarshan, World
Scientific Publishing Compan
Hindered Coulomb explosion of embedded Na clusters -- stopping, shape dynamics and energy transport
We investigate the dynamical evolution of a Na cluster embedded in Ar
matrices of various sizes from N=30 to 1048. The system is excited by an
intense short laser pulse leading to high ionization stages. We analyze the
subsequent highly non-linear motion of cluster and Ar environment in terms of
trajectories, shapes, and energy flow. The most prominent effects are:
temporary stabilization of high charge states for several ps, sudden stopping
of the Coulomb explosion of the embedded Na clusters associated with an
extremely fast energy transfer to the Ar matrix, fast distribution of energy
throughout the Ar layers by a sound wave. Other ionic-atomic transfer and
relaxation processes proceed at slower scale of few ps. The electron cloud is
almost thermally decoupled from ions and thermalizes far beyond the ps scale.Comment: 12 pages, 10 figures, accepted in Euro. Phys. J.
Lectures on Higgs Boson Physics in the Standard Model and Beyond
These lectures focus on the structure of various Higgs boson theories. Topics
in the first lectures include: mass generation in chiral theories, spontaneous
symmetry breaking, neutrino masses, perturbative unitarity, vacuum stability,
vacuum alignment, flavor changing neutral current solutions with multiple Higgs
doublets, analysis of type I theory with Z2 symmetry, and rephasing symmetries.
After an Essay on the Hierarchy Problem, additional topics are covered that
more directly relate to naturalness of the electroweak theory. Emphasis is on
their connection to Higgs boson physics. Topics in these later lectures
include: supersymmetry, supersymmetric Higgs sector in the Runge basis,
leading-order radiative corrections of supersymmetric light Higgs boson mass,
theories of extra dimensions, and radion mixing with the Higgs boson in warped
extra dimensions. And finally, one lecture is devoted to Higgs boson
connections to the hidden sector.Comment: 71 pages, Delivered at Cambridge University and University of
Liverpool, British Universities Summer School (BUSSTEPP 2008 & 2009
Accessing directly the properties of fundamental scalars in the confinement and Higgs phase
The properties of elementary particles are encoded in their respective
propagators and interaction vertices. For a SU(2) gauge theory coupled to a
doublet of fundamental complex scalars these propagators are determined in both
the Higgs phase and the confinement phase and compared to the Yang-Mills case,
using lattice gauge theory. Since the propagators are gauge-dependent, this is
done in the Landau limit of 't Hooft gauge, permitting to also determine the
ghost propagator. It is found that neither the gauge boson nor the scalar
differ qualitatively in the different cases. In particular, the gauge boson
acquires a screening mass, and the scalar's screening mass is larger than the
renormalized mass. Only the ghost propagator shows a significant change.
Furthermore, indications are found that the consequences of the residual
non-perturbative gauge freedom due to Gribov copies could be different in the
confinement and the Higgs phase.Comment: 11 pages, 6 figures, 1 table; v2: one minor error corrected; v3: one
appendix on systematic uncertainties added and some minor changes, version to
appear in EPJ
- âŠ