921,641 research outputs found

### Nonperturbative physics at short distances

There is accumulating evidence in lattice QCD that attempts to locate
confining fields in vacuum configurations bring results explicitly depending on
tha lattice spacing (that is, ultraviolet cut off). Generically, one deals with
low-dimensional vacuum defects which occupy a vanishing fraction of the total
four-dimensional space. We review briefly existing data on the vacuum defects
and their significance for confinement and other nonperturbative phenomena. We
introduce the notion of `quantum numbers' of the defects and draw an analogy,
rather formal one, to developments which took place about 50 years ago and were
triggered by creation of the Sakata model.Comment: 15 pages, contributed to International Symposium on the Jubilee of
the Sakata Model (pnLambda50), Nagoya, Japan, Nov. 200

### Power corrections from short distances

It is argued that power contributions of short distance origin naturally
arise in the infrared finite coupling approach. A phenomenology of $1/Q^2$
power corrections is sketched.Comment: 5 pages, latex, no figures. Expanded version of a talk presented at
the EPS HEP97 Conference (Jerusalem, August 1997

### Quark Pseudo-Distributions at Short Distances

We perform a one-loop study of the small-$z_3^2$ behavior of the Ioffe-time
distribution (ITD) ${\cal M} (\nu, z_3^2)$, the basic function that may be
converted into parton pseudo- and quasi-distributions. We calculate the
corrections at the operator level, so that our results may be later used for
pseudo-distribution amplitudes and generalized parton pseudo-distributions. We
separate two sources of the $z_3^2$-dependence at small $z_3^2$. One is related
to the ultraviolet (UV) singularities generated by the gauge link, and another
to short-distance logarithms generating perturbative evolution of parton
densities. Our calculation explicitly shows that, for a finite UV cut-off, the
UV-singular terms vanish when $z_3^2=0$. The UV divergences are absent in the
ratio ${\cal M} (\nu, z_3^2)/{\cal M} (0, z_3^2)$ ("reduced" ITD). Still, it
has a non-trivial short-distance behavior due to $\ln z_3^2 \Lambda^2$ terms
generating perturbative evolution of the parton densities. We give an explicit
expression, up to constant terms, for the reduced ITD at one loop. It may be
used in extraction of PDFs from the lattice QCD simulations. We also use our
results to get new insights concerning the structure of parton
quasi-distributions at one-loop level.Comment: 10 pages, 4 figures, typos fixed, references added, some changes in
tex

### Short distances, black holes, and TeV gravity

The Hawking effect can be rederived in terms of two-point functions and in
such a way that it makes it possible to estimate, within the conventional
semiclassical theory, the contribution of ultrashort distances at $I^+$ to the
Planckian spectrum. Thermality is preserved for black holes with $\kappa l_P <<
1$. However, deviations from the Planckian spectrum can be found for mini black
holes in TeV gravity scenarios, even before reaching the Planck phase.Comment: 4 pages. Contribution to the MG11 Meeting (Berlin, July 2006

### Dynamical nucleus-nucleus potential at short distances

The dynamical nucleus-nucleus potentials for fusion reactions 40Ca+40Ca,
48Ca+208Pb and 126Sn+130Te are studied with the improved quantum molecular
dynamics (ImQMD) model together with the extended Thomas-Fermi approximation
for the kinetic energies of nuclei. The obtained fusion barrier for 40Ca+40Ca
is in good agreement with the extracted fusion barrier from the measured fusion
excitation function, and the depth of the fusion pockets are close to the
results of time-dependent Hartree-Fock calculations. The energy dependence of
fusion barrier is also investigated. For heavy fusion system, the fusion pocket
becomes shallow and almost disappears for symmetric systems and the obtained
potential at short distances is higher than the adiabatic potential.Comment: 6 figures, accepted for publication in Phys. Rev.

### Monopole clusters at short and large distances

We present measurements of various geometrical characteristics of monopole
clusters in SU(2) lattice gauge theory. The maximal Abelian projection is
employed and both infinite, or percolating cluster and finite clusters are
considered. In particular, we observe scaling for average length of segments of
the percolating cluster between self-crossings, correlators of vacuum monopole
currents, angular correlation between links along trajectories. Short clusters
are random walks and their spectrum in length corresponds to free particles. At
the hadronic scale, on the other hand, the monopole trajectories are no longer
random walks. Moreover, we argue that the data on the density of finite
clusters suggest that there are long-range correlations between finite clusters
which can be understood as association of the clusters with two-dimensional
surfaces, whose area scales.Comment: 9 pages, 11 figure

### Probing Physics at Short Distances with Supersymmetry

We discuss the prospect of studying physics at short distances, such as
Planck length or GUT scale, using supersymmetry as a probe. Supersymmetry
breaking parameters contain information on all physics below the scale where
they are induced. We will gain insights into grand unification (or in some
cases string theory) and its symmetry breaking pattern combining measurements
of gauge coupling constants, gaugino masses and scalar masses. Once the
superparticle masses are known, it removes the main uncertainty in the analysis
of proton decay, flavor violation and electric dipole moments. We will be able
to discuss the consequence of flavor physics at short distances quantitatively.Comment: 20 pages, uses sprocl.sty, psfig.sty, to appear in `Perspectives on
Supersymmetry', World Scientific, Editor G. Kan

### QCD at large and short distances (annotated version)

The formulation of QCD which contains no divergences and no renormalization
procedure is presented. It contains both perturbative and non-perturbative
phenomena. It is shown that, due to its asymptotically free nature, the theory
is not defined uniquely. The chiral symmetry breaking and the nature of the
octet of pseudo-scalar particles as quasi-Goldstone states are analysed in the
theory with massless and massive quarks. The U(1) problem is discussed.
=======================================================================
Note: The original version of the paper completed by the author in April 1997
was submitted to the hep-ph archive (hep-ph/9708424) a few days after Prof.
V.N. Gribov passed away on August 13, 1997.
This is the first of the two papers concluding his 20 year long study of the
problem of quark confinement in QCD. In an attempt to understand the paper by a
group of his colleagues, started in November 1997 in Orsay, this annotated
version appeared. A number of misprints were eliminated, most of the equations
were checked, and some corrected. Comments have been added in order to make the
text easier to read. These comments are displayed in square brackets. Many
theorists participated in the process; the comments were assembled and the
final version prepared by Yu. Dokshitzer, C. Ewerz, A. Kaidalov, A. Mueller, J.
Nyiri and A. Vainshtein. The second paper ``The theory of quark confinement''
will soon be published.Comment: 38 pages, Latex, 108 figures included using epsfig.sty. Annotated
version of hep-ph/9708424, misprints eliminated, equations checked and some
corrected, comments added (see abstract for further details

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