9,551 research outputs found
The Supersymmetric Fine-Tuning Problem and TeV-Scale Exotic Scalars
A general framework is presented for supersymmetric theories that do not
suffer from fine-tuning in electroweak symmetry breaking. Supersymmetry is
dynamically broken at a scale \Lambda \approx (10 - 100) TeV, which is
transmitted to the supersymmetric standard model sector through standard model
gauge interactions. The dynamical supersymmetry breaking sector possesses an
approximate global SU(5) symmetry, whose SU(3) x SU(2) x U(1) subgroup is
explicitly gauged and identified as the standard model gauge group. This SU(5)
symmetry is dynamically broken at the scale \Lambda, leading to
pseudo-Goldstone boson states, which we call xyons. We perform a detailed
estimate for the xyon mass and find that it is naturally in the multi-TeV
region. We study general properties of xyons, including their lifetime, and
study their collider signatures. A generic signature is highly ionizing tracks
caused by stable charged bound states of xyons, which may be observed at the
LHC. We also consider cosmology in our scenario and find that a consistent
picture can be obtained. Our framework is general and does not depend on the
detailed structure of the Higgs sector, nor on the mechanism of gaugino mass
generation.Comment: 53 pages, 7 figure
Quantum Hall Ferromagnetism in Graphene
Graphene is a two-dimensional carbon material with a honeycomb lattice and
Dirac-like low-energy excitations. When Zeeman and spin-orbit interactions are
neglected its Landau levels are four-fold degenerate, explaining the
separation between quantized Hall conductivity values seen in recent
experiments. In this paper we derive a criterion for the occurrence of
interaction-driven quantum Hall effects near intermediate integer values of
due to charge gaps in broken symmetry states.Comment: 4 pages, 1 figur
Viable Ultraviolet-Insensitive Supersymmetry Breaking
It is known that one can add D-term contributions for U(1)_Y and U(1)_{B-L}
to the anomaly-mediated supersymmetry breaking to make the superparticle
spectrum phenomenologically viable. We point out that this can be done without
spoiling its important virtue, namely the ultraviolet insensitivity. This
framework can be derived from supersymmetry breaking and U(1)_{B-L} breaking on
hidden brane(s).Comment: 19 pages, Latex, small clarifications adde
Topological delocalization of two-dimensional massless Dirac fermions
The beta function of a two-dimensional massless Dirac Hamiltonian subject to
a random scalar potential, which e.g., underlies the theoretical description of
graphene, is computed numerically. Although it belongs to, from a symmetry
standpoint, the two-dimensional symplectic class, the beta function
monotonically increases with decreasing . We also provide an argument based
on the spectral flows under twisting boundary conditions, which shows that none
of states of the massless Dirac Hamiltonian can be localized.Comment: 4 pages, 2 figure
Dimension-six top-Higgs interaction and its effect in collider phenomenology
Measurement of the Yukawa interaction between the top quark and the Higgs
boson should be useful to clarify the mechanism of fermion mass generation.
We discuss the impact of non-standard interactions characterized by
dimension-six operators on the effective top Yukawa coupling.
The cross section of the process is calculated including these operators, and possible deviation
from the standard model prediction is evaluated under the constraint from
perturbative unitarity and current experimental data.
We find that if the new physics scale is in a TeV region, the cross section
can be significantly enhanced due to the non-standard interactions.
Such a large effect should be detectable at the International Linear
Collider.Comment: 22 pages, RevTex4, 20 eps figure
Ohmic Contact Formation on N-Type 6H-SiC Using Poly-Si and Silicides
Silicon Carbide with its wide bandgap, high thermal conductivity, and high breakdown electric field is an attractive material to be used for applications in high power, and high temperature semiconductor devices. For such applications, it is extremely important to be able to form stable ohmic contacts. Various metals have been attempted to form ohmic contacts on SiC such as Ni, Ti, and Al. However it has been observed that these metallization schemes have degraded performance due to carbon accumulation by forming carbides at the interface. In this study, polycide (poly Si + silicide) based metallizations have been investigated, using NiSi2 and TiSi2. Silicides of Ni and Ti have been synthesized employing a layer of heavily doped polysilicon to prevent any form of reaction between the metal and the carbon at the SiC interface. Using a 0.5cm2 n-type 6H-SiC samples with various doping concentrations (1.3 x 1018 cm-3 and 1.7 x 1018 cm-3), the electrical and structural properties of NiSi2 and TiSi2 have been examined by fabricating linear transmission line model (TLM) structures. I-V characterization have been carried out to determine the specific contact resistivity, PC. Samples were processed at various annealing temperatures to determine conditions for the best ohmic contact resistivity
Supersymmetry without a Light Higgs Boson
Motivated by the absence, so far, of any direct signal of conventional
low-energy supersymmetry, we explore the consequences of making the lightest
Higgs boson in supersymmetry relatively heavy, up to about 300 GeV, in the most
straightforward way, i.e. via the introduction of a chiral singlet S with a
superpotential interaction with the Higgs doublets, \lambda S H_1 H_2. The
coupling \lambda dominates over all the other couplings and, to maintain the
successful perturbative analysis of the ElectroWeak Precision Tests, is only
restricted to remain perturbative up to about 10 TeV. The general features of
this "\lambda SUSY" framework, which deviates significantly from the MSSM or
the standard NMSSM, are analyzed in different areas: ElectroWeak Precision
Tests, Dark Matter, naturalness bounds on superparticle masses, and LHC
signals. There is a rich Higgs/Higgsino sector in the (200-700)GeV mass region,
which may include LSP Higgsino dark matter. All other superpartners, apart from
the top squarks, may naturally be heavier than 1-2 TeV. This picture can be
made consistent with gauge coupling unification.Comment: 27 page
Disorder-induced metal-insulator transitions in three-dimensional topological insulators and superconductors
We discuss the effects of disorder in time-reversal invariant topological
insulators and superconductors in three spatial dimensions. For
three-dimensional topological insulator in symplectic (AII) symmetry class, the
phase diagram in the presence of disorder and a mass term, which drives a
transition between trivial and topological insulator phases, is computed
numerically by the transfer matrix method. The numerics is supplemented by a
field theory analysis (the large- expansion where is the number of
valleys or Dirac cones), from which we obtain the correlation length exponent,
and several anomalous dimensions at a non-trivial critical point separating a
metallic phase and a Dirac semi-metal. A similar field theory approach is
developed for disorder-driven transitions in symmetry class AIII, CI, and DIII.
For these three symmetry classes, where topological superconductors are
characterized by integer topological invariant, a complementary description is
given in terms of the non-linear sigma model supplemented with a topological
term which is a three-dimensional analogue of the Pruisken term in the integer
quantum Hall effect.Comment: 19 pages, 5 figure
Warped Supersymmetric Unification with Non-Unified Superparticle Spectrum
We present a new supersymmetric extension of the standard model. The model is
constructed in warped space, with a unified bulk symmetry broken by boundary
conditions on both the Planck and TeV branes. In the supersymmetric limit, the
massless spectrum contains exotic colored particles along with the particle
content of the minimal supersymmetric standard model (MSSM). Nevertheless, the
model still reproduces the MSSM prediction for gauge coupling unification and
does not suffer from a proton decay problem. The exotic states acquire masses
from supersymmetry breaking, making the model completely viable, but there is
still the possibility that these states will be detected at the LHC. The
lightest of these states is most likely A_5^XY, the fifth component of the
gauge field associated with the broken unified symmetry. Because supersymmetry
is broken on the SU(5)-violating TeV brane, the gaugino masses generated at the
TeV scale are completely independent of one another. We explore some of the
unusual features that the superparticle spectrum might have as a consequence.Comment: 21 pages, Latex, version to appear in Phys. Rev.
More Visible Effects of the Hidden Sector
There is a growing appreciation that hidden sector dynamics may affect the
supersymmetry breaking parameters in the visible sector (supersymmetric
standard model), especially when the dynamics is strong and superconformal. We
point out that there are effects that have not been previously discussed in the
literature. For example, the gaugino masses are suppressed relative to the
gravitino mass. We discuss their implications in the context of various
mediation mechanisms. The issues discussed include anomaly mediation with
singlets, the mu (B mu) problem in gauge and gaugino mediation, and distinct
mass spectra for the superparticles that have not been previously considered.Comment: 25 pages; small clarifications and corrections, version to appear in
Phys. Rev.
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