14,802 research outputs found
Positive Lyapunov Exponents for Quasiperiodic Szego cocycles
In this paper we first obtain a formula of averaged Lyapunov exponents for
ergodic Szego cocycles via the Herman-Avila-Bochi formula. Then using
acceleration, we construct a class of analytic quasi-periodic Szego cocycles
with uniformly positive Lyapunov exponents. Finally, a simple application of
the main theorem in [Y] allows us to estimate the Lebesgue measure of support
of the measure associated to certain class of C1 quasiperiodic 2- sided
Verblunsky coefficients. Using the same method, we also recover the [S-S]
results for Schrodinger cocycles with nonconstant real analytic potentials and
obtain some nonuniform hyperbolicity results for arbitrarily fixed Brjuno
frequency and for certain C1 potentials.Comment: 27 papge
\phi K^{+}K^{-} production in electron-positron annihilation
In this work we study the e^{+}e^{-}\to\phi K^{+}K^{-} reaction. The leading
order electromagnetic contributions to this process involve the \gamma*\phi\
K^{+}K^{-} vertex function with a highly virtual photon. We calculate this
function at low energies using R\chi PT supplemented with the anomalous term
for the VV'P interactions. Tree level contributions involve the kaon form
factors and the K*K transition form factors. We improve this result, valid for
low photon virtualities, replacing the lowest order terms in the kaon form
factors and K*K transition form factors by the form factors as obtained in
U\chi PT in the former case and the ones extracted from recent data on
e^{+}e^{-}\to KK* in the latter case. We calculate rescattering effects which
involve meson-meson amplitudes. The corresponding result is improved using the
unitarized meson-meson amplitudes containing the scalar poles instead of the
lowest order terms. Using the BABAR value for BR(X\to \phi f_{0})\Gamma (X\to
e^{+} e^{-}), we calculate the contribution from intermediate X(2175). A good
description of data is obtained in the case of destructive interference between
this contribution and the previous ones, but more accurate data on the
isovector K*K transition form factor is required in order to exclude
contributions from an intermediate isovector resonance to e^{+}e^{-}\to \phi\
K^{+}K^{-} around 2.2 GeV.Comment: 21 pages, 17 figures. Revised version to appear in Phys. Rev. D.
Contributions of intermediate X(2175) included. Extraction of form factors
update
Optical turbulence vertical distribution with standard and high resolution at Mt. Graham
A characterization of the optical turbulence vertical distribution (Cn2
profiles) and all the main integrated astroclimatic parameters derived from the
Cn2 and the wind speed profiles above the site of the Large Binocular Telescope
(Mt. Graham, Arizona, US) is presented. The statistic includes measurements
related to 43 nights done with a Generalized Scidar (GS) used in standard
configuration with a vertical resolution Delta(H)~1 km on the whole 20 km and
with the new technique (HVR-GS) in the first kilometer. The latter achieves a
resolution Delta(H)~20-30 m in this region of the atmosphere. Measurements done
in different periods of the year permit us to provide a seasonal variation
analysis of the Cn2. A discretized distribution of Cn2 useful for the Ground
Layer Adaptive Optics (GLAO) simulations is provided and a specific analysis
for the LBT Laser Guide Star system ARGOS (running in GLAO configuration) case
is done including the calculation of the 'gray zones' for J, H and K bands. Mt.
Graham confirms to be an excellent site with median values of the seeing
without dome contribution epsilon = 0.72", the isoplanatic angle theta0 = 2.5"
and the wavefront coherence time tau0= 4.8 msec. We find that the optical
turbulence vertical distribution decreases in a much sharper way than what has
been believed so far in proximity of the ground above astronomical sites. We
find that 50% of the whole turbulence develops in the first 80+/-15 m from the
ground. We finally prove that the error in the normalization of the
scintillation that has been recently put in evidence in the principle of the GS
technique, affects these measurements with an absolutely negligible quantity
(0.04").Comment: 11 figures. MNRAS, accepte
Drastic annealing effects in transport properties of single crystals of the YbNi2B2C heavy fermion system
We report temperature dependent resistivity, specific heat, magnetic
susceptibility and thermoelectric power measurements made on the heavy fermion
system YbNi2B2C, for both as grown and annealed single crystals. Our results
demonstrate a significant variation in the temperature dependent electrical
resistivity and thermoelectric power between as grown crystals and crystals
that have undergone optimal (150 hour, 950 C) annealing, whereas the
thermodynamic properties: (c_p(T) and chi(T)) remain almost unchanged. We
interpret these results in terms of redistributions of local Kondo temperatures
associated with ligandal disorder for a small (~ 1%) fraction of the Yb sites.Comment: 5 pages, 4 figures, submitted to PR
Looking Beyond AFTA: Prospects and Challenges for Inter-regional Trade
The world-trading environment has witnessed the proliferation of regional trading arrangements during the last decade. This development has been accompanied by the perceived threat this may bring to the rules-based multilateral trading system. The Association of Southeast Nations (ASEAN), for its part, has not only reaffirmed its commitment to move forward beyond the ASEAN Free Trade Area (AFTA) and toward a higher level of economic integration, but is also looking at enhanced interaction and closer linkages with other regional groupings. This paper examines the prospects and challenges for expanding AFTA for inter-regional trade by first identifying the elements and principles that should govern such an expansion for it to contribute toward global liberalization. Areas for inter-regional linkages are also identified, highlighting the issues and conflicts that may arise considering the differing objectives and scope that AFTA has with the other trade blocs with which it may want to develop an inter-regional linkage. Some probable arrangements for linking/expanding AFTA with other groupings or non-ASEAN countries are then explored, particularly those involving the Australia-New Zealand Closer Economic Relation (CER), the East Asian Countries and the Andean Community.trade liberalization, trade reforms, trade sector, liberalization, ASEAN, trade policies, Andean Community
Looking Beyond AFTA: Prospects and Challenges for Inter-regional Trade
The world-trading environment has witnessed the proliferation of regional trading arrangements during the last decade. This development has been accompanied by the perceived threat this may bring to the rules-based multilateral trading system. The Association of Southeast Nations (ASEAN), for its part, has not only reaffirmed its commitment to move forward beyond the ASEAN Free Trade Area (AFTA) and toward a higher level of economic integration, but is also looking at enhanced interaction and closer linkages with other regional groupings. This paper examines the prospects and challenges for expanding AFTA for inter-regional trade by first identifying the elements and principles that should govern such an expansion for it to contribute toward global liberalization. Areas for inter-regional linkages are also identified, highlighting the issues and conflicts that may arise considering the differing objectives and scope that AFTA has with the other trade blocs with which it may want to develop an inter-regional linkage. Some probable arrangements for linking/expanding AFTA with other groupings or non-ASEAN countries are then explored, particularly those involving the Australia-New Zealand Closer Economic Relation (CER), the East Asian Countries and the Andean Community.trade liberalization, trade reforms, trade sector, liberalization, ASEAN, trade policies, Andean Community
Star formation history in the solar neighborhood: the link between stars and cosmology
Using a cosmological galactic evolutionary approach to model the Milky Way,
we calculate the star formation history (SFH) of the solar neighborhood. The
good agreement we obtain with the observational inferences suggests that our
physical model describes accurately the long term/large spatial trends of the
local and global Milky Way SFH. In this model, star formation is triggered by
disk gravitational instabilities and self-regulated by an energy balance in the
ISM. The drivers of the SFH are the cosmological gas infall rate and the gas
surface density determined by the primordial spin parameter. A LambdaCDM
cosmology was used throughout.Comment: 8 pages, uses kluwer.cls. Invited talk, to appear in "New Quests in
Stellar Astrophysics: The link between Stars and Cosmology", eds. M. Chavez,
A. Bressan, A. Buzzoni & D. Mayya, Kluwer Academic Publisher
High-Energy Proton-Proton Forward Scattering and Derivative Analyticity Relations
We present the results of several parametrizations to two different ensemble
of data on total cross sections at the highest
center-of-mass energies (including cosmic-ray information). The results are
statistically consistent with two distinct scenarios at high energies. From one
ensemble the prediction for the LHC ( TeV) is mb and from the other, mb. From each
parametrization, and making use of derivative analyticity relations (DAR), we
determine (ratio between the forward real and imaginary parts of the
elastic scattering amplitude). A discussion on the optimization of the DAR in
terms of a free parameter is also presented.In all cases good descriptions of
the experimental data are obtained.Comment: One formula added, one unit changed, small misprints corrected, final
version to be published in Brazilian Journal of Physics; 13 pages, 8 figures,
aps-revte
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