18,887 research outputs found
Octet baryon magnetic moments from QCD sum rules
A comprehensive study is made for the magnetic moments of octet baryons in
the method of QCD sum rules. A complete set of QCD sum rules is derived using
the external field method and generalized interpolating fields. For each
member, three sum rules are constructed from three independent tensor
structures. They are analyzed in conjunction with the corresponding mass sum
rules. The performance of each of the sum rules is examined using the criteria
of OPE convergence and ground-state dominance, along with the role of the
transitions in intermediate states. Individual contributions from the u, d and
s quarks are isolated and their implications in the underlying dynamics are
explored. Valid sum rules are identified and their predictions are obtained.
The results are compared with experiment and previous calculations.Comment: 21 pages, 11 figures, 6 figures; added a reference, minor change in
tex
Methods for Measuring New-Physics Parameters in B Decays
Recently, it was argued that new-physics (NP) effects in B decays can be
approximately parametrized in terms of a few quantities. As a result, CP
violation in the system allows one not only to detect the presence of new
physics (NP), but also to measure its parameters. This will allow a partial
identification of the NP, before its production at high-energy colliders. In
this paper, we examine three methods for measuring NP parameters. The first
uses a technique involving both \btos and \btod penguin B decays. Depending
on which pair of decays is used, the theoretical error is in the range 5--15%.
The second involves a comparison of and decays.
Although the theoretical error is large (\gsim 25%), the method can be
performed now, with presently-available data. The third is via a time-dependent
angular analysis of \bvv decays. In this case, there is no theoretical error,
but the technique is experimentally challenging, and the method applies only to
those NP models whose weak phase is universal to all NP operators. A reliable
identification of the NP will involve the measurement of the NP parameters in
many different ways, and with as many B decay modes as possible, so that it
will be important to use all of these methods.Comment: 33 pages, latex, no figures. Appendix added. Analysis and conclusions
unchange
Tau contamination in the platinum channel at neutrino factories
The platinum channel (\nu_e or anti-\nu_e appearance) has been proposed at
neutrino factories as an additional channel that could help in lifting
degeneracies and improving sensitivities to neutrino oscillation parameters,
viz., \theta_{13}, \delta_{CP}, mass hierarchy, deviation of \theta_{23} from
maximality and its octant. This channel corresponds to \nu_\mu -> \nu_e (or the
corresponding anti-particle) oscillations of the initial neutrino flux, with
the subsequent detection of (positrons) electrons from charged current
interactions of the (anti-) \nu_e in the detector. For small values of
\theta_{13}, the dominant \nu_\mu \to \nu_\tau (or corresponding anti-particle)
oscillation results in this signal being swamped by electrons arising from the
leptonic decay of taus produced in charge-current interactions of \nu_\tau
(anti-\nu_\tau) with the detector. We examine for the first time the role of
this tau contamination to the electron events sample and find that it plays a
significant role in the platinum channel compared to other channels, not only
at high energy neutrino factories but surprisingly even at low energy neutrino
factories. Even when the platinum channel is considered in combination with
other channels such as the golden (muon appearance) or muon disappearance
channel, the tau contamination results in a loss in precision of the measured
parameters.Comment: 13 pages latex file with 10 eps figure file
Collective behavior of stock price movements in an emerging market
To investigate the universality of the structure of interactions in different
markets, we analyze the cross-correlation matrix C of stock price fluctuations
in the National Stock Exchange (NSE) of India. We find that this emerging
market exhibits strong correlations in the movement of stock prices compared to
developed markets, such as the New York Stock Exchange (NYSE). This is shown to
be due to the dominant influence of a common market mode on the stock prices.
By comparison, interactions between related stocks, e.g., those belonging to
the same business sector, are much weaker. This lack of distinct sector
identity in emerging markets is explicitly shown by reconstructing the network
of mutually interacting stocks. Spectral analysis of C for NSE reveals that,
the few largest eigenvalues deviate from the bulk of the spectrum predicted by
random matrix theory, but they are far fewer in number compared to, e.g., NYSE.
We show this to be due to the relative weakness of intra-sector interactions
between stocks, compared to the market mode, by modeling stock price dynamics
with a two-factor model. Our results suggest that the emergence of an internal
structure comprising multiple groups of strongly coupled components is a
signature of market development.Comment: 10 pages, 10 figure
Response to sub-threshold stimulus is enhanced by spatially heterogeneous activity
Sub-threshold stimuli cannot initiate excitations in active media, but
surprisingly as we show in this paper, they can alter the time-evolution of
spatially heterogeneous activity by modifying the recovery dynamics. This
results in significant reduction of waveback velocity which may lead to spatial
coherence, terminating all activity in the medium including spatiotemporal
chaos. We analytically derive model-independent conditions for which such
behavior can be observed.Comment: 5 pages, 5 figure
On the superposition principle in interference experiments
The superposition principle is usually incorrectly applied in interference
experiments. This has recently been investigated through numerics based on
Finite Difference Time Domain (FDTD) methods as well as the Feynman path
integral formalism. In the current work, we have derived an analytic formula
for the Sorkin parameter which can be used to determine the deviation from the
application of the principle. We have found excellent agreement between the
analytic distribution and those that have been earlier estimated by numerical
integration as well as resource intensive FDTD simulations. The analytic handle
would be useful for comparing theory with future experiments. It is applicable
both to physics based on classical wave equations as well as the
non-relativistic Schrodinger equation.Comment: 8 pages, 4 figures, To appear in Scientific Reports (Nature
Core-tube morphology of multiwall carbon nanotubes
The present paper investigates the cross-sectional morphology of Multiwalled
Carbon Nanotubes (MWNTs) restrained radially and circumferentially by an
infinite surrounding elastic medium, subjected to uniform external hydrostatic
pressure. In this study, a two-dimensional plane strain model is developed,
assuming no variation of load and deformation along the tube axis. We find some
characteristic cross-sectional shapes from the elastic buckling analysis. The
effect of the surrounded elastic medium on the cross-sectional shape which
occurs due to pressure buckling is focused on by the comparison with the shape
for no elastic medium case in our discussion. It is suggested that in no
embedded elastic medium cases, the cross-sectional shapes of inner tubes
maintain circle or oval; on the other hand, an embedded medium may cause inner
tube corrugation modes especially when the number of shells for MWNTs is small.Comment: 7 figures, 2 figure
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