9,582 research outputs found
Simple Scheme for Gauge Mediation
We present a simple scheme for constructing models that achieve successful
gauge mediation of supersymmetry breaking. In addition to our previous work [1]
that proposed drastically simplified models using metastable vacua of
supersymmetry breaking in vector-like theories, we show there are many other
successful models using various types of supersymmetry breaking mechanisms that
rely on enhanced low-energy U(1)_R symmetries. In models where supersymmetry is
broken by elementary singlets, one needs to assume U(1)_R violating effects are
accidentally small, while in models where composite fields break supersymmetry,
emergence of approximate low-energy U(1)_R symmetries can be understood simply
on dimensional grounds. Even though the scheme still requires somewhat small
parameters to sufficiently suppress gravity mediation, we discuss their
possible origins due to dimensional transmutation. The scheme accommodates a
wide range of the gravitino mass to avoid cosmological problems.Comment: 13 page
Stable skyrmions from extra dimensions
We show that skyrmions arising from compact five dimensional models have
stable sizes. We numerically obtain the skyrmion configurations and calculate
their size and energy. Although their size strongly depends on the magnitude of
localized kinetic-terms, their energy is quite model-independent ranging
between 50-65 times F_pi^2/m_rho, where F_pi is the Goldstone decay constant
and m_rho the lowest Kaluza-Klein mass. These skyrmion configurations
interpolate between small 4D YM instantons and 4D skyrmions made of Goldstones
and a massive vector boson. Contrary to the original 4D skyrmion and previous
5D extensions, these configurations have sizes larger than the inverse of the
cut-off scale and therefore they are trustable within our effective 5D
approach. Such solitonic particles can have interesting phenomenological
consequences as they carry a conserved topological charge analogous to baryon
number.Comment: 20 pages, 3 figure
Level spectroscopy of the square-lattice three-state Potts model with a ferromagnetic next-nearest-neighbor coupling
We study the square-lattice three-state Potts model with the ferromagnetic
next-nearest-neighbor coupling at finite temperature. Using the
level-spectroscopy method, we numerically analyze the excitation spectrum of
the transfer matrices and precisely determine the global phase diagram. Then we
find that, contrary to a previous result based on the finite-size scaling, the
massless region continues up to the decoupling point with criticality in the antiferromagnetic region. We also check the universal
relations among excitation levels to provide the reliability of our result.Comment: 4 pages, 2 figure
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
Comparison of crystal structures and effects of Co substitution in a new member of Fe-1111 superconductor family AeFeAsF(Ae = Ca and Sr): a possible candidate for higher Tc superconductor
We refined crystal structures of newly found members of the Fe-1111
superconductor family, CaFe\_{1-x}Co\_{x}AsF and SrFe\_{1-x}Co\_{x}AsF (x = 0,
0.06, 0.12) by powder synchrotron X-ray diffraction analysis. The tetragonal to
orthorhombic phase transitions were observed at ~120 K for unsubstituted
CaFeAsF and at ~180 K for unsubstituted SrFeAsF, the transition temperatures
agreeing with kinks observed in temperature-dependent resistivity curves.
Although the transition temperature decreases, the structural phase transitions
were observed below 100 K in both samples of x = 0.06, and finally they were
suppressed in the doping level of x = 0.12. The refined structures reveal that
distortions of the FeAs4 tetrahedron from the regular tetrahedron likely
originate from mismatches in atomic radii among the constituent elements. In
this system, the enlarged FeAs4 tetrahedron resulting from larger radius of Sr
than that of Ca is flattened along a-b plane, whereas the smaller radius of Ca
makes the tetrahedron closer to regular one, and their characteristic shapes
are further enhanced by Co substitution. These results suggest that the CaFeAsF
compound is a promising candidate for higher-Tc superconductor.Comment: 17 pages, 8 figures, 2 tables, Supplementary information is included
at the end of the documen
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.
The Cosmological Constant in the Quantum Multiverse
Recently, a new framework for describing the multiverse has been proposed
which is based on the principles of quantum mechanics. The framework allows for
well-defined predictions, both regarding global properties of the universe and
outcomes of particular experiments, according to a single probability formula.
This provides complete unification of the eternally inflating multiverse and
many worlds in quantum mechanics. In this paper we elucidate how cosmological
parameters can be calculated in this framework, and study the probability
distribution for the value of the cosmological constant. We consider both
positive and negative values, and find that the observed value is consistent
with the calculated distribution at an order of magnitude level. In particular,
in contrast to the case of earlier measure proposals, our framework prefers a
positive cosmological constant over a negative one. These results depend only
moderately on how we model galaxy formation and life evolution therein.Comment: 18 pages, 4 figures; matches the version published in Phys. Rev.
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