135 research outputs found
The NNLO QCD analysis of the CCFR data for xF_3: is there still the room for the twist-4 terms?
The results of the more detailed NNLO QCD analysis of the CCFR data for
SF are presented. The factorization scale uncertainties are analysed.
The NNLO results for and twist-4 contributions are obtained.
Despite the fact that the amplitude of the -shape of the twist-4 factor is
consequently decreasing at the NLO and NNLO, our new QCD analysis seems to
reveal the remaining twist-4 structure at the NNLO level. The definite NLO
uncertainties are fixed using the [0/2] Pad\'e resummation technique.Comment: LaTeX, 3 pages, 1 figure; to be published in the Proceedings of DIS99
Workshop, Zeuthen, April 19-23; some technical shortcomings are fixed in the
file, 2 referencies correcte
Smartphone Spectrometers
Smartphones are playing an increasing role in the sciences, owing to the ubiquitous proliferation of these devices, their relatively low cost, increasing processing power and their suitability for integrated data acquisition and processing in a 'lab in a phone' capacity. There is furthermore the potential to deploy these units as nodes within Internet of Things architectures, enabling massive networked data capture. Hitherto, considerable attention has been focused on imaging applications of these devices. However, within just the last few years, another possibility has emerged: to use smartphones as a means of capturing spectra, mostly by coupling various classes of fore-optics to these units with data capture achieved using the smartphone camera. These highly novel approaches have the potential to become widely adopted across a broad range of scientific e.g., biomedical, chemical and agricultural application areas. In this review, we detail the exciting recent development of smartphone spectrometer hardware, in addition to covering applications to which these units have been deployed, hitherto. The paper also points forward to the potentially highly influential impacts that such units could have on the sciences in the coming decades
Hard exclusive meson production at next-to-leading order
We evaluate perturbative next-to-leading order corrections to the hard
exclusive leptoproduction of pi+ mesons on a transversely polarized proton
target. A model dependent study shows that these corrections can be large. We
analyze the scale dependence and explore the Brodsky-Lepage-Mackenzie scale
setting procedure. Although the predictions for the cross section suffer from
theoretical uncertainties, the transverse nucleon single spin asymmetry turns
out to be a rather stable observable since higher order effects approximately
cancel there.Comment: 14 pages, LaTeX, 3 figure
Infinite N phase transitions in continuum Wilson loop operators
We define smoothed Wilson loop operators on a four dimensional lattice and
check numerically that they have a finite and nontrivial continuum limit. The
continuum operators maintain their character as unitary matrices and undergo a
phase transition at infinite N reflected by the eigenvalue distribution closing
a gap in its spectrum when the defining smooth loop is dilated from a small
size to a large one. If this large N phase transition belongs to a solvable
universality class one might be able to calculate analytically the string
tension in terms of the perturbative Lambda-parameter. This would be achieved
by matching instanton results for small loops to the relevant large-N-universal
function which, in turn, would be matched for large loops to an effective
string theory. Similarities between our findings and known analytical results
in two dimensional space-time indicate that the phase transitions we found only
affect the eigenvalue distribution, but the traces of finite powers of the
Wilson loop operators stay smooth under scaling.Comment: 31 pages, 9 figures, typos and references corrected, minor
clarifications adde
Exact noncommutative solitons in p-adic strings and BSFT
The tachyon field of p-adic string theory is made noncommutative by replacing
ordinary products with noncommutative products in its exact effective action.
The same is done for the boundary string field theory, treated as the p -> 1
limit of the p-adic string. Solitonic lumps corresponding to D-branes are
obtained for all values of the noncommutative parameter theta. This is in
contrast to usual scalar field theories in which the noncommutative solitons do
not persist below a critical value of theta. As theta varies from zero to
infinity, the solution interpolates smoothly between the soliton of the p-adic
theory (respectively BSFT) to the noncommutative soliton.Comment: 1+14 pages (harvmac b), 1 eps figure, v2: references added, typos
correcte
Problem of a quantum particle in a random potential on a line revisited
The density of states for a particle moving in a random potential with a
Gaussian correlator is calculated exactly using the functional integral
technique. It is achieved by expressing the functional degrees of freedom in
terms of the spectral variables and the parameters of isospectral
transformations of the potential. These transformations are given explicitly by
the flows of the Korteweg-de Vries hierarchy which deform the potential leaving
all its spectral properties invariant. Making use of conservation laws reduces
the initial Feynman integral to a combination of quadratures which can be
readily calculated. Different formulations of the problem are analyzed.Comment: 11 pages, RevTex, preprint ANU-RSPhySE-20994 (comment added
N^3LO fits to xF_3 data : vs 1/Q^2 contributions
The results of approximate N^3LO and detailed NNLO fits to data of
the CCFR'97 collaboration are presented. We demonstrate that
non-perturbative corrections to modeled by three independent procedures
are shadowed by perturbative QCD effects, starting at the NNLO. Special
attention is paid to revealing the role of the recently calculated NNLO
corrections to the anomalous dimensions and LO corrections to the
coefficient functions of odd moments of with . The related
values of are extracted.Comment: 5 pages, 1 figure, LaTeX; Contributed to the Proceedings of joint 6th
Symposium RADCOR 2002 and 6th Zeuthen Workshop Loops and Legs in Quantum
Field Theory, September 8-13, Kloster Banz, Germany; size of postscript
figure fixe
Drell-Yan production at small q_T, transverse parton distributions and the collinear anomaly
Using methods from effective field theory, an exact all-order expression for
the Drell-Yan cross section at small transverse momentum is derived directly in
q_T space, in which all large logarithms are resummed. The anomalous dimensions
and matching coefficients necessary for resummation at NNLL order are given
explicitly. The precise relation between our result and the
Collins-Soper-Sterman formula is discussed, and as a by-product the previously
unknown three-loop coefficient A^(3) is obtained. The naive factorization of
the cross section at small transverse momentum is broken by a collinear
anomaly, which prevents a process-independent definition of x_T-dependent
parton distribution functions. A factorization theorem is derived for the
product of two such functions, in which the dependence on the hard momentum
transfer is separated out. The remainder factors into a product of two
functions of longitudinal momentum variables and x_T^2, whose
renormalization-group evolution is derived and solved in closed form. The
matching of these functions at small x_T onto standard parton distributions is
calculated at O(alpha_s), while their anomalous dimensions are known to three
loops.Comment: 32 pages, 2 figures; version to appear in Eur. Phys. J.
Spectrum of confining strings in SU(N) gauge theories
We study the spectrum of the confining strings in four-dimensional SU(N)
gauge theories. We compute, for the SU(4) and SU(6) gauge theories formulated
on a lattice, the string tensions sigma_k related to sources with Z_N charge k,
using Monte Carlo simulations. Our results are consistent with the sine formula
sigma_k/sigma = sin k pi/N / sin pi/N for the ratio between sigma_k and the
standard string tension sigma.
For the SU(4) and SU(6) cases the accuracy is approximately 1% and 2%,
respectively. The sine formula is known to emerge in various realizations of
supersymmetric SU(N) gauge theories. On the other hand, our results show
deviations from Casimir scaling. We also discuss an analogous behavior
exhibited by two-dimensional SU(N) x SU(N) chiral models.Comment: Latex, 34 pages, 10 figures. Results of new SU(4) simulations added.
The new data are included in the analysis, leading to improved final
estimates for SU(4). Conclusions unchange
Event Shape/Energy Flow Correlations
We introduce a set of correlations between energy flow and event shapes that
are sensitive to the flow of color at short distances in jet events. These
correlations are formulated for a general set of event shapes, which includes
jet broadening and thrust as special cases. We illustrate the method for
electron-positron annihilation dijet events, and calculate the correlation at
leading logarithm in the energy flow and at next-to-leading-logarithm in the
event shape.Comment: 43 pages, eight eps figures; minor changes, references adde
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