138 research outputs found
The critical region of strong-coupling lattice QCD in different large-N limits
We study the critical behavior at nonzero temperature phase transitions of an
effective Hamiltonian derived from lattice QCD in the strong-coupling
expansion. Following studies of related quantum spin systems that have a
similar Hamiltonian, we show that for large and fixed , mean
field scaling is not expected, and that the critical region has a finite width
at . A different behavior rises for and fixed
and , which we study in two spatial dimensions and for . We
find that the width of the critical region is suppressed by with
, and argue that a generalization to and to three dimensions
will change this only in detail (e.g. the value of ), but not in
principle. We conclude by stating under what conditions this suppression is
expected, and remark on possible realizations of this phenomenon in lattice
gauge theories in the continuum.Comment: 24 pages, 6 figures. New version includes: a more extensive
discussion of strong-coupling expansions and their region of validity.
Accordingly I have reworded the descriptions of the investigated limits.
Removed typos and misprint
The closed string spectrum of SU(N) gauge theories in 2+1 dimensions
We use lattice techniques to study the closed-string spectrum of SU(N) gauge
theories in 2+1 dimensions. We calculate the energies of the lowest lying ~30
states for strings with lengths between l ~ 0.45 fm and l ~ 3 fm, and compare
to different theoretical predictions. We obtain unambiguous evidence that the
closed-strings are in the universality class of the Nambu-Goto free bosonic
string. Moreover, we clearly see that our data can be described by a covariant
string theory with a small/moderate correction down to very short distance
scales, and possibly on all distance scales at large-N.Comment: 21 pages, 9 figures, 3 table
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