10,941 research outputs found
Muon anomalous magnetic moment in supersymmetric scenarios with an intermediate scale and nonuniversality
We analyze the anomalous magnetic moment of the muon (a_{\mu}) in
supersymmetric scenarios. First we concentrate on scenarios with universal soft
terms. We find that a moderate increase of a_{\mu} can be obtained by lowering
the unification scale M_{GUT} to intermediate values 10^{10-12} GeV. However,
large values of \tan \beta are still favored. Then we study the case of
non-universal soft terms. For the usual value M_{GUT}~10^{16} GeV, we obtain
a_{\mu} in the favored experimental range even for moderate \tan \beta regions
\tan\beta ~ 5$. Finally, we give an explicit example of these scenarios. In
particular, we show that in a D-brane model, where the string scale is
naturally of order 10^{10-12} GeV and the soft terms are non universal, a_{\mu}
is enhanced with low \tan\beta.Comment: Final version to appear in Phys. Rev. D. Conventions clarified,
results in the figures improve
Relic Neutralino Density in Scenarios with Intermediate Unification Scale
We analyse the relic neutralino density in supersymmetric models with an
intermediate unification scale. In particular, we present concrete cosmological
scenarios where the reheating temperature is as small as
MeV). When this temperature is associated to the decay of moduli fields
producing neutralinos, we show that the relic abundance increases considerably
with respect to the standard thermal production. Thus the neutralino becomes a
good dark matter candidate with 0.1\lsim \Omega h^2 \lsim 0.3, even for
regions of the parameter space where large neutralino-nucleon cross sections,
compatible with current dark matter experiments, are present. This is obtained
for intermediate scales GeV, and moduli masses
GeV. On the other hand, when the above temperature is
associated to the decay of an inflaton field, the relic abundance is too small.Comment: Latex, 11 pages, 2 figure
Supersymmetric contributions to B -> D K and the determination of angle \gamma
We analyze supersymmetric contributions to B^- -> D^0 K^- and B^- ->\bar{D}^0
K^- processes. We investigate the possibility that supersymmetric CP violating
phases can affect our determination for the angle \gamma in the unitary
triangle of Cabibbo-Kobayashi-Maskaw mixing matrix. We calculate the gluino and
chargino contributions to b--> u(\bar{c}s) and b-->c(\bar{u}s) transitions in a
model independent way by using the mass insertion approximation method. We also
revise the D^0 - \bar{D}^0 mixing constraints on the mass insertions between
the first and second generations of the up sector. We emphasize that in case of
negligible D^0 -\bar{D}^0 mixing, one should consider simultaneous
contributions from more than one mass insertion in order to be able to obtain
the CP asymmetries of these processes within their 1\sigma experimental range.
However, with a large D^0-\bar{D}^0 mixing, one finds a significant deviation
between the two asymmetries and it becomes natural to have them of order the
central values of their experimental measurements.Comment: 20 page
Optical properties of nanowires based on a blend of poly (9,9-dioctylfluorene) [PFO] and poly(9,9-dioctyl fluorene-alt-benzothiadiazole) [F8BT]
Near-field and far-field optical microscopy are used to study the optical properties of nanowires based on a blend of 95% poly (9,9-dioctylfluorene) [PFO] doped with 5% poly (9,9-dioctylfluorene-alt-benzothiadiazole) [F8BT]. Single nanowires were imaged and optical investigations revealed that they act as nanoscale optical waveguides. Investigation using polarization-resolved far-field PL spectroscopy revealed emission from the nanowires was strongly anisotropic having preferred axial polarization. This suggests that a significant number of the polymer chains are oriented along the nanowire axis
Sterile neutrino dark matter in extension of the standard model and galactic 511 keV line
Sterile right-handed neutrinos can be naturally embedded in a low scale
gauged extension of the standard model. We show that, within a low
reheating scenario, such a neutrino is an interesting candidate for dark
matter. We emphasize that if the neutrino mass is of order of MeV, then it
accounts for the measured dark matter relic density and also accommodates the
observed flux of 511 keV photons from the galactic bulge.Comment: 10 pages, 1 figure, references added, final version appeared in JCA
Adaptive Horizon Model Predictive Control and Al'brekht's Method
A standard way of finding a feedback law that stabilizes a control system to
an operating point is to recast the problem as an infinite horizon optimal
control problem. If the optimal cost and the optmal feedback can be found on a
large domain around the operating point then a Lyapunov argument can be used to
verify the asymptotic stability of the closed loop dynamics. The problem with
this approach is that is usually very difficult to find the optimal cost and
the optmal feedback on a large domain for nonlinear problems with or without
constraints. Hence the increasing interest in Model Predictive Control (MPC).
In standard MPC a finite horizon optimal control problem is solved in real time
but just at the current state, the first control action is implimented, the
system evolves one time step and the process is repeated. A terminal cost and
terminal feedback found by Al'brekht's methoddefined in a neighborhood of the
operating point is used to shorten the horizon and thereby make the nonlinear
programs easier to solve because they have less decision variables. Adaptive
Horizon Model Predictive Control (AHMPC) is a scheme for varying the horizon
length of Model Predictive Control (MPC) as needed. Its goal is to achieve
stabilization with horizons as small as possible so that MPC methods can be
used on faster and/or more complicated dynamic processes.Comment: arXiv admin note: text overlap with arXiv:1602.0861
Constraining supersymmetric models from B_d - B-bar_d mixing and the B_d --> J/psi K_S asymmetry
We analyze the chargino contributions to B_d - B-bar_d mixing and CP
asymmetry of the B_d --> J/psi K_S decay, in the framework of the mass
insertion approximation. We derive model independent bounds on the relevant
mass insertions. Moreover, we study these contributions in supersymmetric
models with minimal flavor violation, Hermitian flavor structure, and small CP
violating phases and universal strength Yukawa couplings. We show that in
supersymmetric models with large flavor mixing, the observed values of sin(2
beta) may be entirely due to the chargino-up-squark loops.Comment: 22 pages, 1 figure, minor corrections, version to appear in Phys.
Rev.
Solving the SUSY CP problem with flavor breaking F-terms
Supersymmetric flavor models for the radiative generation of fermion masses
offer an alternative way to solve the SUSY-CP problem. We assume that the
supersymmetric theory is flavor and CP conserving. CP violating phases are
associated to the vacuum expectation values of flavor violating susy-breaking
fields. As a consequence, phases appear at tree level only in the soft
supersymmetry breaking matrices. Using a U(2) flavor model as an example we
show that it is possible to generate radiatively the first and second
generation of quark masses and mixings as well as the CKM CP phase. The
one-loop supersymmetric contributions to EDMs are automatically zero since all
the relevant parameters in the lagrangian are flavor conserving and as a
consequence real. The size of the flavor and CP mixing in the susy breaking
sector is mostly determined by the fermion mass ratios and CKM elements. We
calculate the contributions to epsilon, epsilon^{prime} and to the CP
asymmetries in the B decays to psi Ks, phi Ks, eta^{\prime} Ks and Xs gamma. We
analyze a case study with maximal predictivity in the fermion sector. For this
worst case scenario the measurements of Delta mK, Delta mB and epsilon
constrain the model requiring extremely heavy squark spectra.Comment: 21 pages, RevTex
On supersymmetric contributions to the CP asymmetry of the B -> phi K_S
We analyse the CP asymmetry of the B -> phi K_S process in general
supersymmetric models. In the framework of the mass insertion approximation, we
derive model independent limits for the mixing CP asymmetry. We show that
chromomagnetic type of operator may play an important role in accounting for
the deviation of the mixing CP asymmetry between B -> phi K_S and B -> J/psi
K_S processes observed by Belle and BaBar experiments. A possible correlation
between the direct and mixing CP asymmetry is also discussed. Finally, we apply
our result in minimal supergravity model and supersymmetric models with
non-universal soft terms.Comment: 19 pages, 3 figure
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