259 research outputs found
Top-Down Approach to Unified Supergravity Models
We introduce a new approach for studying unified supergravity models. In this
approach all the parameters of the grand unified theory (GUT) are fixed by
imposing the corresponding number of low energy observables. This determines
the remaining particle spectrum whose dependence on the low energy observables
can now be investigated. We also include some SUSY threshold corrections that
have previously been neglected. In particular the SUSY threshold corrections to
the fermion masses can have a significant impact on the Yukawa coupling
unification.Comment: 19 pages, uuencoded compressed ps file, DESY 94-057 (paper format
corrected
Production of neutral MSSM Higgs bosons in collisions: a complete 1-loop calculation
We present the first complete 1-loop diagrammatic calculation of the cross
sections for the neutral Higgs production processes e^+e^-\ra Z^0h^0 and
e^+e^-\ra A^0h^0 in the minimal supersymmetric standard model. We compare the
results from the diagrammatic calculation with the corresponding ones of the
simpler and compact effective potential approximation and discuss the typical
size of the differences.Comment: LaTeX, 16 pages, 8 figures appended in a uuencoded file, complete
PostScript file available at
http://itpaxp1.physik.uni-karlsruhe.de/prep/KA-TP-16-1995/KA-TP-16-199
Possible Gauge Theoretic Origin for Quark-Lepton Complementarity
Similarity between the weak interaction properties of quarks and leptons has
led to suggestions that the origin of lepton mixing angles may be related to
those of quarks. In this paper, we present a gauge model based on group that leads to a new form for the quark
lepton complementarity which predicts the solar neutrino mixing angle in terms
of the Cabibbo angle for the case of inverted mass hierarchy for neutrinos. We
also indicate how these ideas can be implemented in an inspired
trinification model, which is more
closely allied to string theory by the AdS/CFT correspondence.Comment: 9 pages, latex, no figures; presentation improved; results unchanged;
minor typos correcte
Complete two-loop effective potential approximation to the lightest Higgs scalar boson mass in supersymmetry
I present a method for accurately calculating the pole mass of the lightest
Higgs scalar boson in supersymmetric extensions of the Standard Model, using a
mass-independent renormalization scheme. The Higgs scalar self-energies are
approximated by supplementing the exact one-loop results with the second
derivatives of the complete two-loop effective potential in Landau gauge. I
discuss the dependence of this approximation on the choice of renormalization
scale, and note the existence of particularly poor choices which fortunately
can be easily identified and avoided. For typical input parameters, the
variation in the calculated Higgs mass over a wide range of renormalization
scales is found to be of order a few hundred MeV or less, and is significantly
improved over previous approximations.Comment: 5 pages, 1 figure. References added, sample test model parameters
listed, minor wording change
Scale-independent mixing angles
A radiatively-corrected mixing angle has to be independent of the choice of
renormalization scale to be a physical observable. At one-loop in MS-bar, this
only occurs for a particular value, p*, of the external momentum in the
two-point functions used to define the mixing angle: p*^2=(M1^2+M2^2)/2, where
M1, M2 are the physical masses of the two mixed particles. We examine two
important applications of this to the Minimal Supersymmetric Standard Model:
the mixing angle for a) neutral Higgs bosons and b) stops. We find that this
choice of external momentum improves the scale independence (and therefore
provides a more reliable determination) of these mixing angles.Comment: 14 pages, 11 ps figures Version to appear in PR
FACT - Monitoring Blazars at Very High Energies
The First G-APD Cherenkov Telescope (FACT) was built on the Canary Island of
La Palma in October 2011 as a proof of principle for silicon based photosensors
in Cherenkov Astronomy. The scientific goal of the project is to study the
variability of active galatic nuclei (AGN) at TeV energies. Observing a small
sample of TeV blazars whenever possible, an unbiased data sample is collected.
This allows to study the variability of the selected objects on timescales from
hours to years. Results from the first three years of monitoring will be
presented. To provide quick flare alerts to the community and trigger
multi-wavelength observations, a quick look analysis has been installed on-site
providing results publicly online within the same night. In summer 2014,
several flare alerts were issued. Results of the quick look analysis are
summarized.Comment: 2014 Fermi Symposium proceedings - eConf C14102.
Data compression for the First G-APD Cherenkov Telescope
The First Geiger-mode Avalanche photodiode (G-APD) Cherenkov Telescope (FACT)
has been operating on the Canary island of La Palma since October 2011.
Operations were automated so that the system can be operated remotely. Manual
interaction is required only when the observation schedule is modified due to
weather conditions or in case of unexpected events such as a mechanical
failure. Automatic operations enabled high data taking efficiency, which
resulted in up to two terabytes of FITS files being recorded nightly and
transferred from La Palma to the FACT archive at ISDC in Switzerland. Since
long term storage of hundreds of terabytes of observations data is costly, data
compression is mandatory. This paper discusses the design choices that were
made to increase the compression ratio and speed of writing of the data with
respect to existing compression algorithms.
Following a more detailed motivation, the FACT compression algorithm along
with the associated I/O layer is discussed. Eventually, the performances of the
algorithm is compared to other approaches.Comment: 17 pages, accepted to Astronomy and Computing special issue on
astronomical file format
(B-L) Symmetry vs. Neutrino Seesaw
We compute the effective coupling of the Majoron to W bosons at \cO(\hbar)
by evaluating the matrix element of the (B-L) current between the vacuum and a
state. The (B-L) anomaly vanishes, but the amplitude does not vanish
as a result of a UV finite and non-local contribution which is entirely due to
the mixing between left-chiral and right-chiral neutrinos. The result shows how
anomaly-like couplings may arise in spite of the fact that the (B-L) current
remains exactly conserved to all orders in , lending additional support
to our previous proposal to identify the Majoron with the axion.Comment: 13 pages, 1 figure, with additional explanations and clarification
Are Messages of R-parity Violating Supersymmetry Hidden within Top Quark Signals ?
In an R-parity nonconserving supersymmetric theory, the lighter stop can
dominantly decay into and if R-parity breaking has to explain
the neutrino mass and mixing pattern suggested by the data on atmospheric muon
neutrinos. This should give rise to and ,
signals resembling those of the top quark at the Fermilab Tevatron. One can
thus constrain the stop parameter space using the current top search data, and
similarly look for the first signals of supersymmetry at the upgraded runs of
the Tevatron.Comment: 13 pages, RevTeX, 2 PS figures, uses epsfig.sty, few comments and
references added, version to appear in Phys. Rev. Let
Calibration and performance of the photon sensor response of FACT -- The First G-APD Cherenkov telescope
The First G-APD Cherenkov Telescope (FACT) is the first in-operation test of
the performance of silicon photo detectors in Cherenkov Astronomy. For more
than two years it is operated on La Palma, Canary Islands (Spain), for the
purpose of long-term monitoring of astrophysical sources. For this, the
performance of the photo detectors is crucial and therefore has been studied in
great detail. Special care has been taken for their temperature and voltage
dependence implementing a correction method to keep their properties stable.
Several measurements have been carried out to monitor the performance. The
measurements and their results are shown, demonstrating the stability of the
gain below the percent level. The resulting stability of the whole system is
discussed, nicely demonstrating that silicon photo detectors are perfectly
suited for the usage in Cherenkov telescopes, especially for long-term
monitoring purpose
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