61,542 research outputs found
Observations of Galactic Gamma-Ray Sources with H.E.S.S
H.E.S.S. results from the first three years of nominal operation are
presented. Among the many exciting measurements that have been made, most
gamma-ray sources are of Galactic origin. I will concentrate here on an
overview of Galactic observations and summarise and discuss observations of
selected objects of the different source types.Comment: 13 pages, 10 figures, based on a talk presented at the workshop
'Energy Budget in the High Energy Universe', Kashiwa, Japan 22 - 24 February
200
Studying the nuclear mass composition of Ultra-High Energy Cosmic Rays with the Pierre Auger Observatory
The Fluorescence Detector of the Pierre Auger Observatory measures the
atmospheric depth, , where the longitudinal profile of the high energy
air showers reaches its maximum. This is sensitive to the nuclear mass
composition of the cosmic rays. Due to its hybrid design, the Pierre Auger
Observatory also provides independent experimental observables obtained from
the Surface Detector for the study of the nuclear mass composition. We present
-distributions and an update of the average and RMS values in
different energy bins and compare them to the predictions for different nuclear
masses of the primary particles and hadronic interaction models. We also
present the results of the composition-sensitive parameters derived from the
ground level component.Comment: Proceedings of the 12th International Conference on Topics in
Astroparticle and Underground Physics, TAUP 2011, Munich, German
Jet-hadron correlations in STAR
Advancements in full jet reconstruction have made it possible to use jets as
triggers in azimuthal angular correlations to study the modification of
hard-scattered partons in the medium created in ultrarelativistic heavy-ion
collisions. This increases the range of parton energies accessible in these
analyses and improves the signal-to-background ratio compared to dihadron
correlations. Results of a systematic study of jet-hadron correlations in
central Au-Au collisions at sqrt(s_NN) = 200 GeV are indicative of a broadening
and softening of jets which interact with the medium. Furthermore, jet-hadron
correlations suggest that the suppression of the associated hadron yield at
high-pT is balanced in large part by low-pT enhancement.Comment: 4 pages, 2 figures, proceedings for Quark Matter 201
Is "just-so" Higgs splitting needed for t-b-\tau Yukawa unified SUSY GUTs?
Recent renormalization group calculations of the sparticle mass spectrum in
the Minimal Supersymmetric Standard Model (MSSM) show that t-b-\tau Yukawa
coupling unification at M_{\rm GUT} is possible when the mass spectra follow
the pattern of a radiatively induced inverted scalar mass hierarchy. The
calculation is entirely consistent with expectations from SO(10) SUSY GUT
theories, with one exception: it seems to require MSSM Higgs soft term mass
splitting at M_{\rm GUT}, dubbed "just-so Higgs splitting" (HS) in the
literature, which apparently violates the SO(10) gauge symmetry. Here, we
investigate three alternative effects: {\it i}). SO(10) D-term splitting, {\it
ii}). inclusion of right hand neutrino in the RG calculation, and {\it iii}).
first/third generation scalar mass splitting. By combining all three effects
(the DR3 model), we find t-b-\tau Yukawa unification at M_{\rm GUT} can be
achieved at the 2.5% level. In the DR3 case, we expect lighter (and possibly
detectable) third generation and heavy Higgs scalars than in the model with HS.
In addition, the light bottom squark in DR3 should be dominantly a right state,
while in the HS model, it is dominantly a left state.Comment: 21 pages with 11 .eps figures; revised version added two reference
Kinetics of spin coherence of electrons in an undoped semiconductor quantum well
We study the kinetics of spin coherence of optically excited electrons in an
undoped insulating ZnSe/ZnCdSe quantum well under moderate magnetic
fields in the Voigt configuration. After clarifying the optical coherence and
the spin coherence, we build the kinetic Bloch equations and calculate
dephasing and relaxation kinetics of laser pulse excited plasma due to
statically screened Coulomb scattering and electron hole spin exchange. We find
that the Coulomb scattering can not cause the spin dephasing, and that the
electron-hole spin exchange is the main mechanism of the spin decoherence.
Moreover the beat frequency in the Faraday rotation angle is determined mainly
by the Zeeman splitting, red shifted by the Coulomb scattering and the electron
hole spin exchange. Our numerical results are in agreement with experiment
findings. A possible scenario for the contribution of electron-hole spin
exchange to the spin dephasing of the -doped material is also proposed.Comment: 12 pages, RevTex, 11 figures, scheduled to publish in PRB Jan. 15,
200
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