3,446 research outputs found
Brane Supersymmetry Breaking
We show how to construct chiral tachyon-free perturbative orientifold models,
where supersymmetry is broken at the string scale on a collection of branes
while, to lowest order, the bulk and the other branes are supersymmetric. In
higher orders, supersymmetry breaking is mediated to the remaining sectors, but
is suppressed by the size of the transverse space or by the distance from the
brane where supersymmetry breaking primarily occurred. This setting is of
interest for orbifold models with discrete torsion, and is of direct relevance
for low-scale string models. It can guarantee the stability of the gauge
hierarchy against gravitational radiative corrections, allowing an almost exact
supergravity a millimeter away from a non-supersymmetric world.Comment: 15 pages, LaTe
Brane to bulk supersymmetry breaking and radion force at micron distances
We study mediation of supersymmetry breaking in the bulk, in models with
primordial supersymmetry breaking on D-branes at the string scale, in the TeV
region. We compute the gravitino and scalar masses up to one-loop level, as
well as the radion coupling to matter. We find that the latter mediates a model
independent force at submillimeter distances that can be tested in
micro-gravity experiments for any dimensionality of the bulk. In the case of
two large dimensions, our type I string framework provides an example which
allows to stabilize the radion potential and determine the desired hierarchy
between the string and Planck scales.Comment: One equation and one figure corrected. Two references added. Version
to be published in Nuclear Physics
Soft Masses in Theories with Supersymmetry Breaking by TeV-Compactification
We study the sparticle spectroscopy and electroweak breaking of theories
where supersymmetry is broken by compactification (Scherk-Schwarz mechanism) at
a TeV. The evolution of the soft terms above the compactification scale and the
resulting sparticle spectrum are very different from those of the usual MSSM
and gauge mediated theories. This is traced to the softness of the
Scherk-Schwarz mechanism which leads to scalar sparticle masses that are only
logarithmically sensitive to the cutoff starting at two loops. As a result,
squarks and sleptons are naturally an order of magnitude lighter than gauginos.
In addition, the mechanism is very predictive and the sparticle spectrum
depends on just two new parameters. A significant advantage of this mechanism
relative to gauge mediation is that a Higgsino mass is
automatically generated when supersymmetry is broken. Our analysis applies
equally well to theories where the cutoff is near a TeV or or some
intermediate scale. We also use these observations to show how we may obtain
compactification radii which are hierarchically larger than the fundamental
cutoff scale.Comment: 26 pages, 1 figure, Late
Axion alternatives
If recent results of the PVLAS collaboration proved to be correct, some
alternative to the traditional axion models are needed. We present one of the
simplest possible modifications of axion paradigm, which explains the results
of PVLAS experiment, while avoiding all the astrophysical and cosmological
restrictions. We also mention other possible models that possess similar
effects.Comment: 12 pages, 3 figure
One-loop Higgs mass finiteness in supersymmetric Kaluza-Klein theories
We analyze the one-loop ultraviolet sensitivity of the Higgs mass in a
five-dimensional supersymmetric theory compactified on the orbifold S^1/Z_2,
with superpotential localized on a fixed-point brane. Four-dimensional
supersymmetry is broken by Scherk-Schwarz boundary conditions. Kaluza-Klein
interactions are regularized by means of a brane Gaussian distribution along
the extra dimension with length l_s\simeq\Lambda^{-1}_s, where \Lambda_s is the
cutoff of the five-dimensional theory. The coupling of the n-mode, with mass
M^{(n)}, acquires the n-dependent factor exp{-(M^{(n)}/\Lambda_s)^2/2}, which
makes it to decouple for M^{(n)}\gg \Lambda_s. The sensitivity of the Higgs
mass on \Lambda_s is strongly suppressed and quadratic divergences cancel by
supersymmetry. The one-loop correction to the Higgs mass is finite and equals,
for large values of \Lambda_s, the value obtained by the so-called
KK-regularization.Comment: 8 pages, 1 figure. The discussion on the distribution giving rise to
couplings suppressed by exp(-M/Lambda) is revised and the result is finite
and equals that of the Gaussian cas
Magnetic fluxes and moduli stabilization
Stabilization of closed string moduli in toroidal orientifold
compactifications of type IIB string theory are studied using constant internal
magnetic fields on D-branes and 3-form fluxes that preserve N=1 supersymmetry
in four dimensions. Our analysis corrects and extends previous work by us, and
indicates that charged scalar VEV's need to be turned on, in addition to the
fluxes, in order to construct a consistent supersymmetric model. As an explicit
example, we first show the stabilization of all Kahler class and complex
structure moduli by turning on magnetic fluxes on different sets of D9-branes
that wrap the internal space T^6 in a compactified type I string theory, when a
charged scalar on one of these branes acquires a non-zero VEV. The latter can
also be determined by adding extra magnetized branes, as we demonstrate in a
subsequent example. In a different model with magnetized D7-branes, in a IIB
orientifold on T^6/Z_2, we show the stabilization of all the closed string
moduli, including the axion-dilaton at weak string coupling g_s, by turning on
appropriate closed string 3-form fluxes.Comment: v2: minor changes, added discussio
Supersymmetry breaking, open strings and M-theory
We study supersymmetry breaking by Scherk-Schwarz compactifications in type I
string theory. While in the gravitational sector all mass splittings are
proportional to a (large) compactification radius, supersymmetry remains
unbroken for the massless excitations of D-branes orthogonal to the large
dimension. In this sector, supersymmetry breaking can then be mediated by
gravitational interactions alone, that are expected to be suppressed by powers
of the Planck mass. The mechanism is non perturbative from the heterotic
viewpoint and requires a compactification radius at intermediate energies of
order 10^{12}-10^{14} GeV. This can also explain the value of Newton's constant
if the string scale is close to the unification scale, of order 10^{16} GeV.Comment: 47 pages, LaTeX, typos correcte
A Multiproject Chip Approach to the Teaching of Analog MOS LSI and VLSI
Multiproject chip implementation has been used in teaching analog MOS circuit design. After having worked with computer simulation and layout aids in homework problems, students designed novel circuits including several high
performance op amps, an A/D converter, a switched capacitor filter, a 1 K dynamic RAM, and a variety of less conventional MOS circuits such as a VII converter, an AC/DC converter, an AM radio receiver, a digitally-controlled
analog signal processor, and on-chip circuitry for measuring transistor capacitances. These circuits were laid out as part of an NMOS multiproject chip. Several of the designs exhibit a considerable degree of innovation;
fabrication pending, computer simulation shows that some may be pushing the state of the art. Several designs are of interest to digital designers; in fact, the course has provided knowledge and technique needed for detailed
digital circuit design at the gate level
Moduli stabilization with open and closed string fluxes
We study the stabilization of all closed string moduli in the T^6/Z_2
orientifold, using constant internal magnetic fields and 3-form fluxes that
preserve N=1 supersymmetry in four dimensions. We first analyze the
stabilization of Kahler class and complex structure moduli by turning on
magnetic fluxes on different sets of D9 branes that wrap the internal space
T^6/Z_2. We present explicit consistent string constructions, satisfying in
particular tadpole cancellation, where the radii can take arbitrarily large
values by tuning the winding numbers appropriately. We then show that the
dilaton-axion modulus can also be fixed by turning on closed string constant
3-form fluxes, consistently with the supersymmetry preserved by the magnetic
fields, providing at the same time perturbative values for the string coupling.
Finally, several models are presented combining open string magnetic fields
that fix part of Kahler class and complex structure moduli, with closed string
3-form fluxes that stabilize the remaining ones together with the dilaton.Comment: 49 pages, a new model added, as well as improvements and reference
Scherk-Schwarz Supersymmetry Breaking with Radion Stabilization
We study the issue of radion stabilization within five-dimensional
supersymmetric theories compactified on the orbifold S^1/Z_2. We break
supersymmetry by the Scherk-Schwarz mechanism and explain its implementation in
the off-shell formulation of five dimensional supergravity in terms of the
tensor and linear compensator multiplets. We show that radion stabilization may
be achieved by radiative corrections in the presence of five-dimensional fields
which are quasi-localized on the boundaries through the presence of Z_2 odd
mass terms. For the mechanism to work the number of quasi-localized fields
should be greater than 2+N_V-N_h where N_V and N_h are the number of massless
gauge- and hypermultiplets in the bulk. The radion is stabilized in a
metastable Minkowski vacuum with a lifetime much larger than cosmological
time-scales. The radion mass is in the meV range making it interesting for
present and future measurements of deviations from the gravitational
inverse-square law in the submillimeter range.Comment: 16 pages, 4 figure
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