14,666 research outputs found

### Perturbative Confinement

A Procedure is outlined that may be used as a starting point for a
perturbative treatment of theories with permanent confinement. By using a
counter term in the Lagrangian that renormalizes the infrared divergence in the
Coulomb potential, it is achieved that the perturbation expansion at a finite
value of the strong coupling constant may yield reasonably accurate properties
of hadrons, and an expression for the string constant as a function of the QCD
Lambda parameter.Comment: Presented at QCD'02, Montpellier, July 2002. 12 pages LaTeX, 8
Figures PostScript, uses gthstyle.sty Reprt-no: ITF-2002/39; SPIN-2002/2

### TransPlanckian Particles and the Quantization of Time

Trans-Planckian particles are elementary particles accelerated such that
their energies surpass the Planck value. There are several reasons to believe
that trans-Planckian particles do not represent independent degrees of freedom
in Hilbert space, but they are controlled by the cis-Planckian particles. A way
to learn more about the mechanisms at work here, is to study black hole
horizons, starting from the scattering matrix Ansatz.
By compactifying one of the three physical spacial dimensions, the scattering
matrix Ansatz can be exploited more efficiently than before. The algebra of
operators on a black hole horizon allows for a few distinct representations. It
is found that this horizon can be seen as being built up from string bits with
unit lengths, each of which being described by a representation of the SO(2,1)
Lorentz group. We then demonstrate how the holographic principle works for this
case, by constructing the operators corresponding to a field in space-time. The
parameter t turns out to be quantized in Planckian units, divided by the period
R of the compactified dimension.Comment: 12 pages plain tex, 1 figur

### Geometry of Scattering at Planckian Energies

We present an alternative derivation and geometrical formulation of Verlinde
topological field theory, which may describe scattering at center of mass
energies comparable or larger than the Planck energy. A consistent trunckation
of 3+1 dimensional Einstein action is performed using the standard geometrical
objects, like tetrads and spin connections. The resulting topological invariant
is given in terms of differential forms.Comment: 8

### Winding Solutions for the two Particle System in 2+1 Gravity

Using a PASCAL program to follow the evolution of two gravitating particles
in 2+1 dimensions we find solutions in which the particles wind around one
another indefinitely. As their center of mass moves `tachyonic' they form a
Gott-pair. To avoid unphysical boundary conditions we consider a large but
closed universe. After the particles have evolved for some time their momenta
have grown very large. In this limit we quantize the model and find that both
the relevant configuration variable and its conjugate momentum become discrete.Comment: 15 pages Latex, 4 eps figure

### Can Electro-Weak \h-Term be Observable ?

We rederive and discuss the result of the previous paper that in the standard
model $\theta$-term related to $W$-boson field can not be induced by weak
instantons. This follows from the existence of the fermion zero mode in the
instanton field even when Yukawa couplings are switched on and there are no
massless particles. We consider the new index theorem connecting the
topological charge of the weak gauge field with the number of fermion zero
modes of a certain differential operator which depends not only on gauge but
also on Higgs fields. The possible generalizations of the standard model are
discussed which lead to nonvanishing weak $\theta$-term. In $SU(2)_L \times
SU(2)_R$ model the $\theta$ dependence of the vacuum energy is computed.Comment: 21 pages, Preprint TPI-MINN-93/24-

### Quantization of Space and Time in 3 and in 4 Space-time Dimensions

The fact that in Minkowski space, space and time are both quantized does not
have to be introduced as a new postulate in physics, but can actually be
derived by combining certain features of General Relativity and Quantum
Mechanics. This is demonstrated first in a model where particles behave as
point defects in 2 space dimensions and 1 time, and then in the real world
having 3+1 dimensions. The mechanisms in these two cases are quite different,
but the outcomes are similar: space and time form a (non-cummutative) lattice.
These notes are short since most of the material discussed in these lectures
is based on two earlier papers by the same author (gr-qc/9601014 and
gr-qc/9607022), but the exposition given in the end is new.Comment: Lectures held at the NATO Advanced Study Institute on ``Quantum
Fields and Quantum Space Time", Carg\`ese, July 22 -- August 3, 1996. 16
pages Plain TeX, 6 Figure

### Thermal photon dispersion law and modified black-body spectra

Based on the postulate that photon propagation is governed by an SU(2) gauge
principle we numerically compute the one-loop dispersion for thermalized photon
propagation on the radiatively induced mass shell. Formerly, the dispersion was
addressed by assuming $p^2=0$. While this approximation turns out to be
excellent for temperatures $\le 2 T_{\tiny{CMB}}$ the exact result exhibits a
much faster (power-like) shrinking of the gap in the black-body spectral
intensity with rising temperature. Our previous statements on anomalous
large-angle CMB temperature-temperature correlations, obtained in the
approximation $p^2=0$, remain valid.Comment: v2: 13 pages, 6 figures; sec. 2.1. added to explain effective theory;
references added; matches journal published versio

### Pauli-Lubanski scalar in the Polygon Approach to 2+1-Dimensional Gravity

In this paper we derive an expression for the conserved Pauli-Lubanski scalar
in 't Hooft's polygon approach to 2+1-dimensional gravity coupled to point
particles. We find that it is represented by an extra spatial shift $\Delta$ in
addition to the usual identification rule (being a rotation over the cut). For
two particles this invariant is expressed in terms of 't Hooft's phase-space
variables and we check its classical limit.Comment: Some errors are corrected and a new introduction and discussion are
added. 6 pages Latex, 4 eps-figure

### Are magnetic monopoles hadrons?

The charges of magnetic monopoles are constrained to a multiple of $2\pi$
times the inverse of the elementary unit electric charge. In the standard
model, quarks have fractional charge, raising the question of whether the basic
magnetic monople unit is a multiple of $2 \pi/e$ or three times that. A simple
lattice construction shows how a magnetic monopole of the lower strength is
possible if it interacts with gluonic fields as well. Such a monopole is thus a
hadron. This is consistent with the construction of magnetic monopoles in grand
unified theories.Comment: Poster presented at Lattice2004(topology), Fermilab, June 21-26,
2004. 3 pages, 5 figure

### Heavy meson semileptonic decays in two dimensions in the large Nc

We study QCD in 1+1 dimensions in the large Nc limit using light-front
Hamiltonian perturbation theory in the 1/Nc expansion. We use this formalism to
exactly compute hadronic transition matrix elements for arbitrary currents at
leading order in 1/Nc, which we use to write the semileptonic differential
decay rate of a heavy meson and its moments. We then compare with the results
obtained using an effective field theory approach based on perturbative
factorization, with the intention of better understanding quark-hadron duality.
A very good numerical agreement is obtained between the exact result and the
result using effective theories.Comment: Talk given at the High-Energy Physics International Conference on
Quantum Chromodynamics, 3-7 July (2006), Montpellier (France

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