1,266 research outputs found
On threshold resummation beyond leading 1-x order
We check against exact finite order three-loop results for the non-singlet
F_2 and F_3 structure functions the validity of a class of momentum space
ansaetze for threshold resummation at the next-to-leading order in 1-x, which
generalize results previously obtained in the large-\beta_0 limit. We find that
the ansaetze do not work exactly, pointing towards an obstruction to threshold
resummation at this order, but still yield correct results at the leading
logarithmic level for each color structures, as well as at the
next-to-next-to-leading logarithmic level for the specific C_F^3 color factor.
A universality of the leading logarithm contributions to the physical evolution
kernels of F_2 and F_3 at the next-to-leading order in 1-x is observed.Comment: v1:18 pages; v2: 26 pages, expanded version with new results for the
F_3 structure function and added references; v3: more concise sections 3 and
4, improved discussion in section 5, added references, to be published in
JHE
Fixing the conformal window in QCD
A physical characterization of Landau singularities is emphasized, which
should trace the lower boundary N_f^* of the conformal window in QCD and
supersymmetric QCD. A natural way to disentangle ``perturbative'' from
``non-perturbative'' contributions to amplitudes below N_f^* is suggested.
Assuming an infrared fixed point persists in the perturbative part of the QCD
coupling even below N_f^* leads to the condition \gamma(N_f^*)=1, where \gamma
is the critical exponent. Using the Banks-Zaks expansion, one gets 4<N_f^*<6.
This result is incompatible with the existence of an analogue of Seiberg
duality in QCD. The presence of a negative ultraviolet fixed point is required
both in QCD and in supersymmetric QCD to preserve causality within the
conformal window. Evidence for the existence of such a fixed point in QCD is
provided.Comment: 10 pages, 1 figure, extended version of a talk given at the
QCDNET2000 meeting, Paris, September 11-14 2000; main new material added is
evidence for negative ultraviolet fixed point in QC
On next-to-eikonal exponentiation
The eikonal approximation is at the heart of many theoretical and
phenomenological studies involving multiple soft gauge boson emissions in high
energy physics. We describe our efforts towards the extension of the eikonal
approximation for scattering amplitudes to the first subleading power in the
soft momentum.Comment: Proc. of "Loops and Legs in Quantum Field Theory", April, 2010,
W\"orlitz, German
Nonperturbative Contributions in an Analytic Running Coupling of QCD
In the framework of analytic approach to QCD the nonperturbative
contributions in running coupling of strong interaction up to 4-loop order are
obtained in an explicit form. For all they are shown to be
represented in the form of an expansion in inverse powers of Euclidean momentum
squared. The expansion coefficients are calculated for different numbers of
active quark flavors and for different number of loops taken into
account. On basis of the stated expansion the effective method for precise
calculation of the analytic running coupling can be developed.Comment: 9 pages, LaTeX, 1 table, 1 eps figur
On the macroion virial contribution to the osmotic pressure in charge-stabilized colloidal suspensions
Our interest goes to the different virial contributions to the equation of
state of charged colloidal suspensions. Neglect of surface effects in the
computation of the colloidal virial term leads to spurious and paradoxical
results. This pitfall is one of the several facets of the danger of a naive
implementation of the so called One Component Model, where the micro-ionic
degrees of freedom are integrated out to only keep in the description the
mesoscopic (colloidal) degrees of freedom. On the other hand, due incorporation
of wall induced forces dissolves the paradox brought forth in the naive
approach, provides a consistent description, and confirms that for salt-free
systems, the colloidal contribution to the pressure is dominated by the
micro-ionic one. Much emphasis is put on the no salt case but the situation
with added electrolyte is also discussed
The Importance of Reporting Housing and Husbandry in Rat Research
In 1963, the National Institutes of Health (NIH) first issued guidelines for animal housing and husbandry. The most recent 2010 revision emphasizes animal care “in ways judged to be scientifically, technically, and humanely appropriate” (National Institutes of Health, 2010, p. XIII). The goal of these guidelines is to ensure humanitarian treatment of animals and to optimize the quality of research. Although these animal care guidelines cover a substantial amount of information regarding animal housing and husbandry, researchers generally do not report all these variables (see Table ​Table1).1). The importance of housing and husbandry conditions with respect to standardization across different research laboratories has been debated previously (Crabbe et al., 1999; Van Der Staay and Steckler, 2002; Wahlsten et al., 2003; Wolfer et al., 2004; Van Der Staay, 2006; Richter et al., 2010, 2011). This paper focuses on several animal husbandry and housing issues that are particularly relevant to stress responses in rats, including transportation, handling, cage changing, housing conditions, light levels and the light–dark cycle. We argue that these key animal housing and husbandry variables should be reported in greater detail in an effort to raise awareness about extraneous experimental variables, especially those that have the potential to interact with the stress response
Infrared Renormalons and Finite Volume
We analyze the perturbative expansion of a condensate in the O(N) non-linear
sigma model for large N on a two dimensional finite lattice. On an infinite
volume this expansion is affected by an infrared renormalon. We extrapolate
this analysis to the case of the gluon condensate of Yang-Mills theory and
argue that infrared renormalons can be detected by performing perturbative
studies even on relatively small lattices.Comment: LaTeX file, 6 figures in postscrip
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