2,140 research outputs found
Layered Higgs Phase as a Possible Field Localisation on a Brane
So far it has been found by using lattice techniques that in the anisotropic
five--dimensional Abelian Higgs model, a layered Higgs phase exists in addition
to the expected five--dimensional one. The exploration of the phase diagram has
shown that the two Higgs phases are separated by a phase transition from the
confining phase. This transition is known to be first order. In this paper we
explore the possibility of finding a second order transition point in the
critical line which separates the first order phase transition from the
crossover region. This is shown to be the case only for the four--dimensional
Higgs layered phase whilst the phase transition to the five--dimensional broken
phase remains first order. The layered phase serves as the possible realisation
of four--dimensional spacetime dynamics which is embedded in a
five--dimensional spacetime. These results are due to gauge and scalar field
localisation by confining interactions along the extra fifth direction.Comment: 1+15 pages, 12 figure
Sneutrino condensate as a candidate for the hot big bang cosmology
If inflationary paradigm is correct, then it must create conditions for the
hot big bang model with all observed matter, baryons and the seed perturbations
for the structure formation. In this paper we propose a scenario where the
inflaton energy density is dumped into the bulk in a brane world setup, and all
the required physical conditions are created by the right handed neutrino
sector within supersymmetry. The scalar component of the right handed Majorana
neutrino is responsible for generating the scale invariant fluctuations in the
cosmic microwave background radiation, reheating the Universe at a
temperature~ GeV, and finally generating the lepton/baryon
asymmetry, , with no lepton/baryon isocurvature
fluctuations.Comment: 19 pages, 3 figures. Some discussion on neutrino masses and
baryogenesis, and other small changes adde
Antiferromagnetically coupled CoFeB/Ru/CoFeB trilayers
This work reports on the magnetic interlayer coupling between two amorphous
CoFeB layers, separated by a thin Ru spacer. We observe an antiferromagnetic
coupling which oscillates as a function of the Ru thickness x, with the second
antiferromagnetic maximum found for x=1.0 to 1.1 nm. We have studied the
switching of a CoFeB/Ru/CoFeB trilayer for a Ru thickness of 1.1 nm and found
that the coercivity depends on the net magnetic moment, i.e. the thickness
difference of the two CoFeB layers. The antiferromagnetic coupling is almost
independent on the annealing temperatures up to 300 degree C while an annealing
at 350 degree C reduces the coupling and increases the coercivity, indicating
the onset of crystallization. Used as a soft electrode in a magnetic tunnel
junction, a high tunneling magnetoresistance of about 50%, a well defined
plateau and a rectangular switching behavior is achieved.Comment: 3 pages, 3 figure
Is There a Peccei-Quinn Phase Transition?
The nature of axion cosmology is usually said to depend on whether the
Peccei-Quinn (PQ) symmetry breaks before or after inflation. The PQ symmetry
itself is believed to be an accident, so there is not necessarily a symmetry
during inflation at all. We explore these issues in some simple models, which
provide examples of symmetry breaking before and after inflation, or in which
there is no symmetry during inflation and no phase transition at all. One
effect of these observations is to relax the constraints from isocurvature
fluctuations due to the axion during inflation. We also observe new
possibilities for evading the constraints due to cosmic strings and domain
walls, but they seem less generic.Comment: 14 pages. Several references adde
Curvaton paradigm can accommodate multiple low inflation scales
Recent arguments show that some curvaton field may generate the cosmological
curvature perturbation. As the curvaton is independent of the inflaton field,
there is a hope that the fine-tunings of inflation models can be cured by the
curvaton scenario. More recently, however, D.H.Lyth discussed that there is a
strong bound for the Hubble parameter during inflation even if one assumes the
curvaton scenario. Although the most serious constraint was evaded, the bound
seems rather crucial for many models of a low inflation scale. In this paper we
try to remove this constraint. We show that the bound is drastically modified
if there were multiple stages of inflation.Comment: 9pages, no figure, references added, final versio
Gauge Unification in Higher Dimensions
A complete 5-dimensional SU(5) unified theory is constructed which, on
compactification on the orbifold with two different Z_2's (Z_2 and Z_2'),
yields the minimal supersymmetric standard model. The orbifold accomplishes
SU(5) gauge symmetry breaking, doublet-triplet splitting, and a vanishing of
proton decay from operators of dimension 5. Until 4d supersymmetry is broken,
all proton decay from dimension 4 and dimension 5 operators is forced to vanish
by an exact U(1)_R symmetry. Quarks and leptons and their Yukawa interactions
are located at the Z_2 orbifold fixed points, where SU(5) is unbroken. A new
mechanism for introducing SU(5) breaking into the quark and lepton masses is
introduced, which originates from the SU(5) violation in the zero-mode
structure of bulk multiplets. Even though SU(5) is absent at the Z_2' orbifold
fixed point, the brane threshold corrections to gauge coupling unification are
argued to be negligibly small, while the logarithmic corrections are small and
in a direction which improves the agreement with the experimental measurements
of the gauge couplings. Furthermore, the X gauge boson mass is lowered, so that
proton decay to e^+ \pi^0 is expected with a rate within about one order of
magnitude of the current limit. Supersymmetry breaking occurs on the Z_2'
orbifold fixed point, and is felt directly by the gauge and Higgs sectors,
while squarks and sleptons acquire mass via gaugino mediation, solving the
supersymmetric flavor problem.Comment: 21 pages, Latex, references added, final versio
Curvaton Potential Terms, Scale-Dependent Perturbation Spectra and Chaotic Initial Conditions
The curvaton scenario predicts an almost scale-invariant spectrum of
perturbations in most inflation models. We consider the possibility that
renormalisable phi^4 or Planck scale-suppressed non-renormalisable curvaton
potential terms may result in an observable deviation from scale-invariance. We
show that if the curvaton initially has a large amplitude and if the total
number of e-foldings of inflation is less than about 300 then a running blue
perturbation spectrum with an observable deviation from scale-invariance is
likely. D-term inflation is considered as an example with a potentially low
total number of e-foldings of inflation. A secondary role for the curvaton, in
which it drives a period of chaotic inflation leading to D-term or other flat
potential inflation from an initially chaotic state, is suggested.Comment: 12 pages LaTeX, minor corrections, to be published in JCA
Supersymmetric photonic signals at LEP
We explore and contrast the single-photon and diphoton signals expected at
LEP 2, that arise from neutralino-gravitino (e^+ e^- -> chi + gravitino ->
gamma + E_miss) and neutralino-neutralino (e^+ e^- -> chi + chi -> gamma +
gamma + E_miss) production in supersymmetric models with a light gravitino. LEP
1 limits imply that one may observe either one, but not both, of these signals
at LEP 2, depending on the values of the neutralino and gravitino masses:
single-photons for m_chi > Mz and m_gravitino < 3 x 10^-5 eV; diphotons for
m_chi < Mz and all allowed values of m_gravitino.Comment: 11 pages, LaTeX, 4 figures (included). Shortened version to appear in
Physical Review Letter
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
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