18 research outputs found
Fermions and Supersymmetry Breaking in the Interval
We study fermions, such as gravitinos and gauginos in supersymmetric
theories, propagating in a five-dimensional bulk where the fifth dimensional
component is assumed to be an interval. We show that the most general boundary
condition at each endpoint of the interval is encoded in a single complex
parameter representing a point in the Riemann sphere. Upon introducing a
boundary mass term, the variational principle uniquely determines the boundary
conditions and the bulk equations of motion. We show the mass spectrum becomes
independent from the Scherk-Schwarz parameter for a suitable choice of one of
the two boundary conditions. Furthermore, for any value of the Scherk-Schwarz
parameter, a zero-mode is present in the mass spectrum and supersymmetry is
recovered if the two complex parameters are tuned.Comment: 10 pages. v2: Paragraph on off-shell globally supersymmetric
Lagrangian added. Version published in PL
Old Inflation in String Theory
We propose a stringy version of the old inflation scenario which does not
require any slow-roll inflaton potential and is based on a specific example of
string compatification with warped metric. Our set-up admits the presence of
anti-D3-branes in the deep infrared region of the metric and a false vacuum
state with positive vacuum energy density. The latter is responsible for the
accelerated period of inflation. The false vacuum exists only if the number of
anti-D3-branes is smaller than a critical number and the graceful exit from
inflation is attained if a number of anti-D3-branes travels from the
ultraviolet towards the infrared region. The cosmological curvature
perturbation is generated through the curvaton mechanism.Comment: 31 pages, 3 figures; typos corrected and reference adde
Supersymmetry breaking with quasi-localized fields in orbifold field theories
We study the Scherk-Schwarz supersymmetry breaking in five-dimensional
orbifold theories with five-dimensional fields which are not strictly localized
on the boundaries (quasi-localized fields). We show that the Scherk-Schwarz
(SS) mechanism, besides the SS parameter \omega, depends upon new parameters,
e.g. supersymmetric five-dimensional odd mass terms, governing the level of
localization on the boundaries of the five-dimensional fields and study in
detail such a dependence. Taking into account radiative corrections, the value
of \omega is dynamically allowed to acquire any value in the range 0< \omega <
1/2.Comment: 13 pages, 3 figure
Low Energy 6-Dimensional N=2 Supersymmertric SU(6) Models on Orbifolds
We propose low energy 6-dimensional N=2 supersymmetric SU(6) models on
and , where the orbifold
model can be embedded on the boundary 4-brane. For the
zero modes, the 6-dimensional N=2 supersymmetry and the SU(6) gauge symmetry
are broken down to the 4-dimensional N=1 supersymmetry and the gauge symmetry by orbifold projections. In
order to cancel the anomalies involving at least one , we add extra
exotic particles. We also study the anomaly free conditions and present some
anomaly free models. The gauge coupling unification can be achieved at TeV if the compactification scale for the fifth dimension is
TeV. The proton decay problem can be avoided by putting the quarks and
leptons/neutrinos on different 3-branes. And we discuss how to break the
gauge symmetry, solve the
problem, and generate the mass hierarchy naturally by using the
geometry. The masses of exotic particles can be at the order of 1 TeV after the
gauge symmetry breaking. We also forbid the dimension-5 operators for the
neutrino masses by gauge symmetry, and the realistic left-handed
neutrino masses can be obtained via non-renormalizable terms.Comment: Latex, 33 pages, discussion and references adde
Cosmology with the Laser Interferometer Space Antenna
The Laser Interferometer Space Antenna (LISA) has two scientific objectives of cosmological focus: to probe the expansion rate of the universe, and to understand stochastic gravitational-wave backgrounds and their implications for early universe and particle physics, from the MeV to the Planck scale. However, the range of potential cosmological applications of gravitational wave observations extends well beyond these two objectives. This publication presents a summary of the state of the art in LISA cosmology, theory and methods, and identifies new opportunities to use gravitational wave observations by LISA to probe the universe