751 research outputs found
Dimension-six Proton Decays in the Modified Missing Doublet SU(5) Model
Dimension-five operators for nucleon decays are suppressed in the modified
missing doublet (MMD) model in the supersymmetric SU(5) grand unification. We
show that nonrenormalizable interactions decrease the unification scale in the
MMD model which increases the nucleon decay rate of dimension-six operators by
a significant amount. We find that the theoretical lower bound on the proton
life time \tau(p \to \e^+ \pi^0) is within the observable range at
SuperKamiokande.Comment: 9 pages, Latex, 1 Postscript figure
A Gauge Mediation Model of Dynamical Supersymmetry Breaking without Color Instability
We construct a gauge mediation model of dynamical supersymmetry breaking
(DSB) based on a vector-like gauge theory, in which there is a unique
color-preserving true vacuum. The DSB scale turns out to be as
high as , since the transmission of the DSB
effects to the standard model sector is completed through much higher loops.
This model is perfectly natural and phenomenologically consistent. We also
stress that the dangerous D-term problem for the messenger U(1)_m is
automatically solved by a charge conjugation symmetry in the vector-like gauge
theory.Comment: 11 pages, Late
Cosmological Constants as Messenger between Branes
We present a supersymmetry-breaking scenario in which both the breaking in
the hidden sector with no-scale type supergravity and that in the observable
sector with gauge mediation are taken into account. The breaking scales in the
hidden and observable sectors are related through the vanishing condition of
the cosmological constant with a brane-world picture in mind. Suppressing
flavor-changing neutral currents, we can naturally obtain the gravitino,
Higgs(ino), and soft masses of the electroweak scale.Comment: 7 pages, Late
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
Supersymmetry, Naturalness, and Signatures at the LHC
Weak scale supersymmetry is often said to be fine-tuned, especially if the
matter content is minimal. This is not true if there is a large A term for the
top squarks. We present a systematic study on fine-tuning in minimal
supersymmetric theories and identify low energy spectra that do not lead to
severe fine-tuning. Characteristic features of these spectra are: a large A
term for the top squarks, small top squark masses, moderately large tan\beta,
and a small \mu parameter. There are classes of theories leading to these
features, which are discussed. In one class, which allows a complete
elimination of fine-tuning, the Higgsinos are the lightest among all the
superpartners of the standard model particles, leading to three nearly
degenerate neutralino/chargino states. This gives interesting signals at the
LHC -- the dilepton invariant mass distribution has a very small endpoint and
shows a particular shape determined by the Higgsino nature of the two lightest
neutralinos. We demonstrate that these signals are indeed useful in realistic
analyses by performing Monte Carlo simulations, including detector simulations
and background estimations. We also present a method that allows the
determination of all the relevant superparticle masses without using input from
particular models, despite the limited kinematical information due to short
cascades. This allows us to test various possible models, which is demonstrated
in the case of a model with mixed moduli-anomaly mediation. We also give a
simple derivation of special renormalization group properties associated with
moduli mediated supersymmetry breaking, which are relevant in a model without
fine-tuning.Comment: 56 pages, 24 figure
Bulk U(1) Messenger
We propose a new U(1) gauge interaction in the bulk in higher dimensional
spacetime, which transmits supersymmetry-breaking effects on the hidden brane
to the observable our brane. We find that rather small gauge coupling constant
of U(1)_{bulk}, , is required for a
successful phenomenology. This result implies the compactification length
of the extra dimension to be for
(4+1)-dimensional spacetime. This large compactification length is a
crucial ingredient to suppress unwanted flavor-changing neutral currents and
hence our proposal is very consistent with the Randall-Sundrum brane-world
scenario.Comment: 9 pages, Late
Re/Os constraint on the time-variability of the fine-structure constant
We argue that the accuracy by which the isochron parameters of the decay
are determined by dating iron meteorites may
not directly constrain the possible time-dependence of the decay rate and hence
of the fine-structure constant . From this point of view, some of the
attempts to analyze the Oklo constraint and the results of the QSO absorption
lines are re-examined.Comment: 7 pages, 3 figures; v2, revised top sentence on p.
ac Losses in a Finite Z Stack Using an Anisotropic Homogeneous-Medium Approximation
A finite stack of thin superconducting tapes, all carrying a fixed current I,
can be approximated by an anisotropic superconducting bar with critical current
density Jc=Ic/2aD, where Ic is the critical current of each tape, 2a is the
tape width, and D is the tape-to-tape periodicity. The current density J must
obey the constraint \int J dx = I/D, where the tapes lie parallel to the x axis
and are stacked along the z axis. We suppose that Jc is independent of field
(Bean approximation) and look for a solution to the critical state for
arbitrary height 2b of the stack. For c<|x|<a we have J=Jc, and for |x|<c the
critical state requires that Bz=0. We show that this implies \partial
J/\partial x=0 in the central region. Setting c as a constant (independent of
z) results in field profiles remarkably close to the desired one (Bz=0 for
|x|<c) as long as the aspect ratio b/a is not too small. We evaluate various
criteria for choosing c, and we show that the calculated hysteretic losses
depend only weakly on how c is chosen. We argue that for small D/a the
anisotropic homogeneous-medium approximation gives a reasonably accurate
estimate of the ac losses in a finite Z stack. The results for a Z stack can be
used to calculate the transport losses in a pancake coil wound with
superconducting tape.Comment: 21 pages, 17 figures, accepted by Supercond. Sci. Techno
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