519 research outputs found
Anomaly Mediation and Dimensional Transmutation
We show how a sparticle spectrum characteristic of anomaly mediation can
arise from a theory whose Lagrangian contains no explicit mass scale. The scale
of supersymmetry breaking is governed by the gravitino mass, which is the
vacuum expectation value of the F-term of the conformal compensator field, and
the tachyonic slepton problem is resolved by the breaking of a U(1) gauge
symmetry at a scale determined by dimensional transmutation.Comment: 12 pages, 1 figure. v2 has added preprint number and acknowledgement
On the origin of duality in the quantum Hall system
We discuss the possible origin of the duality observed in the quantum Hall
current-voltage characteristics. We clarify the difference between
"particle-vortex" (complex modular) duality, which acts on the full transport
tensor, and "charge-flux" ("real") duality, which acts directly on the filling
factor. Comparison with experiment strongly favors the form of duality which
descends from the modular symmetry group acting holomorphically on the
compexified conductivity.Comment: 5 pages, 3 figure
A Minimal Inflation Scenario
We elaborate on a minimal inflation scenario based entirely on the general
properties of supersymmetry breaking in supergravity models. We identify the
inflaton as the scalar component of the Goldstino superfield. We write
plausible candidates for the effective action describing this chiral
superfield. In particular the theory depends (apart from parameters of O(1)) on
a single free parameter: the scale of supersymmetry breaking. This can be fixed
using the amplitude of CMB cosmological perturbations and we therefore obtain
the scale of supersymmetry breaking to be 10^{12-14} GeV. The model also
incorporates explicit R-symmetry breaking in order to satisfy the slow roll
conditions. In our model the eta-problem is solved without extra fine-tuning.
We try to obtain as much information as possible in a model independent way
using general symmetry properties of the theory's effective action, this leads
to a new proposal on how to exit the inflationary phase and reheat the
Universe.Comment: matches published version (typo corrected
Determination of Leading Twist Non-Singlet Operator Matrix Elements by QCD Sum Rules
We use QCD sum rules to determine the twist-two non-singlet operator matrix
elements and fixed x structure functions paying particular regard to the
estimate of the errors. Particularly for the matrix element determination, we
find large uncertainties due to radiative and higher dimension contributions.
We consider the origin of these large corrections and comment on their
consequences for other operator matrix element determinations.Comment: 10 pages, 10 figure
Production of massive stable particles in inflaton decay
We point out that inflaton decays can be a copious source of stable or
long--lived particles with mass exceeding the reheat temperature .
Once higher order processes are included, this statement is true for any
particle with renormalizable (gauge or Yukawa) interactions. This contribution
to the density often exceeds the contribution from thermal
production, leading to significantly stronger constraints on model parameters
than those resulting from thermal production alone. For example, we all
but exclude models containing stable charged particles with mass less than half
the mass of the inflaton.Comment: 4 revtex pages, 1 figure (uses axodraw). Slightly modified for better
clarification, few changes in references. Final verssion published in Phys.
Rev. Let
The fine-tuning cost of the likelihood in SUSY models
In SUSY models, the fine tuning of the electroweak (EW) scale with respect to
their parameters gamma_i={m_0, m_{1/2}, mu_0, A_0, B_0,...} and the maximal
likelihood L to fit the experimental data are usually regarded as two different
problems. We show that, if one regards the EW minimum conditions as constraints
that fix the EW scale, this commonly held view is not correct and that the
likelihood contains all the information about fine-tuning. In this case we show
that the corrected likelihood is equal to the ratio L/Delta of the usual
likelihood L and the traditional fine tuning measure Delta of the EW scale. A
similar result is obtained for the integrated likelihood over the set
{gamma_i}, that can be written as a surface integral of the ratio L/Delta, with
the surface in gamma_i space determined by the EW minimum constraints. As a
result, a large likelihood actually demands a large ratio L/Delta or
equivalently, a small chi^2_{new}=chi^2_{old}+2*ln(Delta). This shows the
fine-tuning cost to the likelihood (chi^2_{new}) of the EW scale stability
enforced by SUSY, that is ignored in data fits. A good
chi^2_{new}/d.o.f.\approx 1 thus demands SUSY models have a fine tuning amount
Delta<<exp(d.o.f./2), which provides a model-independent criterion for
acceptable fine-tuning. If this criterion is not met, one can thus rule out
SUSY models without a further chi^2/d.o.f. analysis. Numerical methods to fit
the data can easily be adapted to account for this effect.Comment: 10 pages (v3: small comment added
Restoring the sting to metric preheating
The relative growth of field and metric perturbations during preheating is
sensitive to initial conditions set in the preceding inflationary phase. Recent
work suggests this may protect super-Hubble metric perturbations from resonant
amplification during preheating. We show that this possibility is fragile and
sensitive to the specific form of the interactions between the inflaton and
other fields. The suppression is naturally absent in two classes of preheating
in which either (1) the vacua of the non-inflaton fields during inflation are
deformed away from the origin, or (2) the effective masses of non-inflaton
fields during inflation are small but during preheating are large. Unlike the
simple toy model of a coupling, most realistic particle
physics models contain these other features. Moreover, they generically lead to
both adiabatic and isocurvature modes and non-Gaussian scars on super-Hubble
scales. Large-scale coherent magnetic fields may also appear naturally.Comment: 6 pages, 3 ps figures, RevTex, revised discussion of backreaction and
new figure. To appear Phys. Rev. D (Rapid Communication
D-term Inflation in Superstring Theories
An inflationary stage dominated by a -term avoids the slow-roll problem of
inflation in supergravity and may emerge in theories with a non-anomalous or
anomalous U(1) gauge symmetry. The most intriguing and commonly invoked
possibility is that the Fayet-Iliopoulos -term triggering inflation is the
one emerging in superstring theories. We discuss the complications one has to
face when trying to build up a successful -term inflationary scenario in
superstring models. In particular, we show that the ``vacuum shifting''
phenomenon of string theories is usually very efficient even in the early
Universe, thus preventing inflation from taking place. On the other hand, when
-term inflation is free to occur, the presence of a plethora of fields and
several non-anomalous additional abelian symmetries in string theories may help
in reconciling the value of the Fayet-Iliopoulos -term required by the COBE
normalization with the value predicted by string theories. We also show that in
superstring -term inflation gravitinos are likely to pose no cosmological
problem.Comment: 19 pages, LaTeX fil
Symmetries and fermion masses
We discuss whether quark, charged lepton and neutrino masses and mixing
angles may be related by an extended flavour and family symmetry group. We show
that current measurements of all fermion masses and mixing angles are
consistent with a combination of an underlying SU(3) family symmetry together
with a GUT symmetry such as SO(10). In this the near bi-maximal mixing observed
in the neutrino sector is directly related to the small mixing observed in the
quark sector, the difference between quark and lepton mixing angles being due
to the see-saw mechanism. Using this connection we make a detailed prediction
for the lepton mixing angles determining neutrino oscillation phenomena.Comment: 24 pages, 1 figure. To be submitted to Nucl. Phys.
Racetrack inflation and assisted moduli stabilisation
We present a model of inflation based on a racetrack model without flux
stabilization. The initial conditions are set automatically through topological
inflation. This ensures that the dilaton is not swept to weak coupling through
either thermal effects or fast roll. Including the effect of non-dilaton fields
we find that moduli provide natural candidates for the inflaton. The resulting
potential generates slow-roll inflation without the need to fine tune
parameters. The energy scale of inflation must be near the GUT scale and the
scalar density perturbation generated has a spectrum consistent with WMAP data.Comment: 17 pages, 6 figures (Latex); Error in v.1 eliminated and improved
example of modular inflation presente
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