1,791 research outputs found
Spin and a Running Radius in RS1
We develop a renormalization group formalism for the compactified
Randall-Sundrum scenario wherein the extra-dimensional radius serves as the
scaling parameter. Couplings on the hidden brane scale as we move within local
effective field theories with varying size of the warped extra dimension. We
consider this RG approach applied to U(1) gauge theories and gravity. We use
this method to derive a low energy effective theory.Comment: 18 pages, minor changes, references adde
Axion-Higgs Unification
In theories with no fundamental scalars, one gauge group can become strong at
a large scale Lambda and spontaneously break a global symmetry, producing the
Higgs and the axion as composite pseudo-Nambu-Goldstone bosons. We show how
KSVZ and DFSZ axion models can be naturally realised. The assumption Lambda
around 10^{11} GeV is phenomenologically favoured because: a) The axion solves
the QCD theta problem and provides the observed DM abundance; b) The observed
Higgs mass is generated via RGE effects from a small Higgs quartic coupling at
the compositeness scale, provided that the Higgs mass term is fine-tuned to be
of electroweak size; c) Lepton, quark as well as neutrino masses can be
obtained from four-fermion operators at the compositeness scale. d) The extra
fermions can unify the gauge couplings.Comment: 19 pages. Refs. added and eq. 3.6 fixe
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TF ripple loss of alpha particles in TFTR DT experiments
Quantitative evaluation of TF ripple loss of DT alpha particles is a central issue for reactor design because of potentially severe first wall heat load problems. DT experiments on TFTR allow experimental measurements to be compared to modeling of the underlying alpha physics, with code validation an important goal. Modeling of TF ripple loss of alphas in TFTR now includes neoclassical calculations of alpha losses arising from first orbit loss, stochastic ripple diffusion, ripple trapping and collisional effects. Recent Hamiltonian coordinate guiding center code (ORBIT) simulations for TFTR have shown that collisions enhance the stochastic TF ripple losses at TFTR. A faster way to simulate experiment has been developed and is discussed here which uses a simple stochastic domain model for TF ripple loss within the TRANSP analysis code
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Calculations of alpha particle loss for reversed magnetic shear in the Tokamak Fusion Test Reactor
Hamiltonian coordinate, guiding center code calculations of the toroidal field ripple loss of alpha particles from a reversed shear plasma predict both total alpha losses and ripple diffusion losses to be greater than those from a comparable non-reversed magnetic shear plasma in the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. High central q is found to increase alpha ripple losses as well as first orbit losses of alphas in the reversed shear simulations. A simple ripple loss model, benchmarked against the guiding center code, is found to work satisfactorily in transport analysis modelling of reversed and monotonic shear scenarios. Alpha ripple transport on TFTR affects ions within r/a=0.5, not at the plasma edge. The entire plasma is above threshold for stochastic ripple loss of alpha particles at birth energy in the reversed shear case simulated, so that all trapped 3.5 MeV alphas are lost stochastically or through prompt losses. The 40% alpha particle loss predictions for TFTR suggest that reduction of toroidal field ripple will be a critical issue in the design of a reversed shear fusion reactor
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Neoclassical Simulations of Fusion Alpha Particles in Pellet Charge Exchange Experiments on the Tokamak Fusion Test Reactor
Neoclassical simulations of alpha particle density profiles in high fusion power plasmas on the Tokamak Fusion Test Reactor (TFTR) [Phys. Plasmas 5 (1998) 1577] are found to be in good agreement with measurements of the alpha distribution function made with a sensitive active neutral particle diagnostic. The calculations are carried out in Hamiltonian magnetic coordinates with a fast, particle-following Monte Carlo code which includes the neoclassical transport processes, a recent first-principles model for stochastic ripple loss and collisional effects. New global loss and confinement domain calculations allow an estimate of the actual alpha particle densities measured with the pellet charge exchange diagnostic
AdS/QCD: The Relevance of the Geometry
We investigate the relevance of the metric and of the geometry in
five-dimensional models of hadrons. Generically, the metric does not affect
strongly the results and even flat space agrees reasonably well with the data.
Nevertheless, we observe a preference for a decreasing warp factor, for example
AdS space. The Sakai-Sugimoto model reduces to one of these models and the
level of agreement is similar to the one of flat space. We also consider the
discrete version of the five-dimensional models, obtained by dimensional
deconstruction. We find that essentially all the relevant features of
"holographic" models of QCD can be reproduced with a simple 3-site model
describing only the states below the cut-off of the theory.Comment: 25 pages + appendix. v2 minor changes and Refs. adde
Natural Supersymmetry at the LHC
If the minimal supersymmetric standard model is the solution to the hierarchy
problem, the scalar top quark (stop) and the Higgsino should weigh around the
electroweak scale such as 200 GeV. A low messenger scale, which results in a
light gravitino, is also suggested to suppress the quantum corrections to the
Higgs mass parameters. Therefore the minimal model for natural supersymmetry is
a system with stop/Higgsino/gravitino whereas other superparticles are heavy.
We study the LHC signatures of the minimal system and discuss the discovery
potential and methods for the mass measurements.Comment: 19 pages, 6 figures, 1 tabl
Implications of a Light Higgs in Composite Models
We study the Higgs mass in composite Higgs models with partial compositeness,
extending the results of Ref. [1] to different representations of the composite
sector for SO(5)/SO(4) and to the coset SO(6)/SO(5). For a given tuning we find
in general a strong correlation between the mass of the top partners and the
Higgs mass, akin to the one in supersymmetry. If the theory is natural a Higgs
mass of 125 GeV typically requires fermionic partners below TeV which might be
within the reach of the present run of LHC. A discussion of CP properties of
both cosets is also presented.Comment: 19 pages, 11 figures. v2) Minor changes, references adde
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Energetic Particle Transport in Compact Quasi-axisymmetric Stellarators
Hamiltonian coordinate, guiding-center code calculations of the confinement of suprathermal ions in quasi-axisymmetric stellarator (QAS) designs have been carried out to evaluate the attractiveness of compact configurations which are optimized for ballooning stability. A new stellarator particle-following code is used to predict ion loss rates and particle confinement for thermal and neutral beam ions in a small experiment with R = 145 cm, B = 1-2 T and for alpha particles in a reactor-size device. In contrast to tokamaks, it is found that high edge poloidal flux has limited value in improving ion confinement in QAS, since collisional pitch-angle scattering drives ions into ripple wells and stochastic field regions, where they are quickly lost. The necessity for reduced stellarator ripple fields is emphasized. The high neutral beam ion loss predicted for these configurations suggests that more interesting physics could be explored with an experiment of less constrained size and magnetic field geometry
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