780 research outputs found
Dynamical Supersymmetry Breaking without Messenger Gauge Interactions
We investigate low-energy models of supersymmetry (SUSY) breaking by means of
vector-like gauge theories for dynamical SUSY breaking. It is not necessary to
introduce messenger gauge interactions utilized so far to mediate the SUSY
breaking to the standard-model sector, which reduces complication in the model
building. We also consider various other ways of SUSY-breaking transmission.Comment: 10 pages, LaTeX, 1 Postscript figur
Interplane and intraplane heat transport in quasi two-dimensional nodal superconductors
We analyze the behavior of the thermal conductivity in quasi-two dimensional
superconductors with line nodes. Motivated by measurements of the anisotropy
between the interplane and intraplane thermal transport in CeIrIn_5 we show
that a simple model of the open Fermi surface with vertical line nodes is
insufficient to describe the data. We propose two possible extensions of the
model taking into account a) additional modulation of the gap along the axial
direction of the open Fermi surface; and b) dependence of the interplane
tunneling on the direction of the in-plane momentum. We discuss the temperature
dependence of the thermal conductivity anisotropy and its low T limit in these
two models and compare the results with a model with a horizontal line of nodes
(``hybrid gap''). We discuss possible relevance of each model for the symmetry
of the order parameter in CeIrIn_5, and suggest further experiments aimed at
clarifying the shape of the superconducting gap.Comment: 14pages, 12 figure
Influence of gap structures to specific heat in oriented magnetic fields: Application to the orbital dependent superconductor, SrRuO
We discuss influence of modulation of gap function and anisotropy of Fermi
velocity to field angle dependences of upper critical field, , and
specific heat, , on the basis of the approximate analytic solution in the
quasiclassical formalism. Using 4-fold modulation of the gap function and the
Fermi velocity in the single-band model, we demonstrate field and temperature
dependence of oscillatory amplitude of and . We apply the method to
the effective two-band model to discuss the gap structure of SrRuO,
focusing on recent field angle-resolved experiments. It is shown that the gap
structures with the intermediate magnitude of minima in direction for
band, and tiny minima of gaps in directions for and
bands give consistent behaviors with experiments. The interplay of the
above two gaps also explains the anomalous temperature dependence of in-plane
anisotropy, where the opposite contribution from the passive
band is pronounced near .Comment: 7 pages, 11 figures in JPSJ forma
A Model of Direct Gauge Mediation
We present a simple model of gauge mediation (GM) which does not have a
messenger sector or gauge singlet fields. The standard model gauge groups
couple directly to the sector which breaks supersymmetry dynamically. This is
the first phenomenologically viable example of this type in the literature.
Despite the direct coupling, the model can preserve perturbative gauge
unification. This is achieved by the inverted hierarchy mechanism which
generates a large scalar expectation value compared to the size of
supersymmetry breaking. There is no dangerous negative contribution to the
squark, slepton masses due to two-loop renormalization group equation. The
potentially non-universal supergravity contribution to the scalar masses can be
suppressed enough to maintain the virtue of the gauge mediation. The model is
completely chiral, and one does not need to forbid mass terms for the messenger
fields by hand. Beyond the simplicity of the model, it possesses cosmologically
desirable features compared to the original models of GM: an improved gravitino
and string moduli cosmology. The Polonyi problem is back unlike in the original
GM models, but is still much less serious than in hidden sector models.Comment: LaTeX, 12 page
General Analysis of Inflation in the Jordan frame Supergravity
We study various inflation models in the Jordan frame supergravity with a
logarithmic Kahler potential. We find that, in a class of inflation models
containing an additional singlet in the superpotential, three types of
inflation can be realized: the Higgs-type inflation, power-law inflation, and
chaotic inflation with/without a running kinetic term. The former two are
possible if the holomorphic function dominates over the non-holomorphic one in
the frame function, while the chaotic inflation occurs when both are
comparable. Interestingly, the fractional-power potential can be realized by
the running kinetic term. We also discuss the implication for the Higgs
inflation in supergravity.Comment: 16 pages, 1 figur
Supercurrent in Nodal Superconductors
In recent years, a number of nodal superconductors have been identified;
d-wave superconductors in high T_c cuprates, CeCoIn, and
\kappa-(ET)_2Cu(NCS)_2, 2D f-wave superconductor in Sr_2RuO_4 and hybrid
s+g-wave superconductor in YNi_2B_2C. In this work we conduct a theoretical
study of nodal superconductors in the presence of supercurrent. For simplicity,
we limit ourselves to d-wave and 2D f-wave superconductors. We compute the
quasiparticle density of states and the temperature dependence of the depairing
critical current in nodal superconductors, both of which are accessible
experimentally.Comment: revtex4, 6 pages, 7 figures; fixed typos, updated references, trimmed
introductio
Magnetic field dependence of superconducting energy gaps in YNi2B2C: Evidence of multiband superconductivity
We present results of in field directional point contact spectroscopy (DPCS)
study in the quaternary borocarbide superconductor YNi2B2C, which is
characterized by a highly anisotropic superconducting gap function. For I||a,
the superconducting energy gap (D), decreases linearly with magnetic field and
vanishes around 3.25T which is well below the upper critical field (Hc2~6T)
measured at the same temperature (2.2K). For I||c, on the other hand, D
decreases weakly with magnetic field but the broadening parameter (G) increases
rapidly with magnetic field with the absence of any resolvable feature above
3.5T. From an analysis of the field variation of energy gaps and the zero bias
density of states we show that the unconventional gap function observed in this
material could originate from multiband superconductivity.Comment: 19 pages including figures (final version
Renormalization Group Invariance of Exact Results in Supersymmetric Gauge Theories
We clarify the notion of Wilsonian renormalization group (RG) invariance in
supersymmetric gauge theories, which states that the low-energy physics can be
kept fixed when one changes the ultraviolet cutoff, provided appropriate
changes are made to the bare coupling constants in the Lagrangian. We first
pose a puzzle on how a quantum modified constraint (such as Pf(Q^i Q^j) =
\Lambda^{2(N+1)} in SP(N) theories with N+1 flavors) can be RG invariant, since
the bare fields Q^i receive wave function renormalization when one changes the
ultraviolet cutoff, while we naively regard the scale \Lambda as RG invariant.
The resolution is that \Lambda is not RG invariant if one sticks to canonical
normalization for the bare fields as is conventionally done in field theory. We
derive a formula for how \Lambda must be changed when one changes the
ultraviolet cutoff. We then compare our formula to known exact results and show
that their consistency requires the change in \Lambda we have found. Finally,
we apply our result to models of supersymmetry breaking due to quantum modified
constraints. The RG invariance helps us to determine the effective potential
along the classical flat directions found in these theories. In particular, the
inverted hierarchy mechanism does not occur in the original version of these
models.Comment: LaTeX, 26 page
Multiple Superconducting Phases in New Heavy Fermion Superconductor PrOs4Sb12
The superconducting gap structure of recently discovered heavy fermion
superconductor PrOs4Sb12 was investigated by using thermal transport
measurements in magnetic field rotated relative to the crystal axes. We
demonstrate that a novel change in the symmetry of the superconducting gap
function occurs deep inside the superconducting state, giving a clear
indication of the presence of two distinct superconducting phases with twofold
and fourfold symmetries. We infer that the gap functions in both phases have a
point node singularity, in contrast to the familiar line node singularity
observed in almost all unconventional superconductors.Comment: 4 Pages, 4 Figure
AC/DC Susceptibility of the Heavy-Fermion Superconductor CePt3Si under Pressure
We have investigated the pressure dependence of ac and dc susceptibilities of
the heavy-fermion superconductor CePt3Si (Tc= 0.75 K) that coexists with
antiferromagnetism (TN = 2.2 K). As hydrostatic pressure is increased, Tc first
decreases rapidly, then rather slowly near the critical pressure Pc = 0.6 GPa
and shows a stronger decrease again at higher pressures, where Pc is the
pressure at which TN becomes zero. A transition width and a difference in the
two transition temperatures defined in the form of structures in the
out-of-phase component of ac susceptibilities also become small near Pc,
indicating that a double transition observed in CePt3Si is caused by some
inhomogeneous property in the sample that leads to a spatial variation of local
pressure. A sudden increase in the Meissner fraction above Pc suggests the
influence of antiferromagnetism on superconductivity.Comment: 4 pages with 5 figures. This paper will be published in J. Phys. Soc.
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