A
bstract
We formulate a method for computing the effective Lagrangian of the Polyakov line on the lattice. Using mean field approximation we calculate the effective potential for high temperatures. ...The result agrees with recent lattice simulations. We reveal a new type of ultraviolet divergence (coming from longitudinal gluons) which dominates the effective potential and explains the discrepancy of the lattice simulations and standard perturbative calculations performed in covariant gauges.
All baryon resonances can be systematized from one and the same point of view, according to what they would look like if the number of colors Nc was large. Although in the real world Nc is only ...three, the consequences of the large-Nc classification are visible in the observed spectrum. At large Nc baryon resonances are collective excitations about intrinsic one-quark or particle-hole states in a certain mean field. Exotic pentaquark baryons appear as `Gamov–Teller' particle-hole excitations. A charmed Bc pentaquark baryon is predicted which may well be so light that it is stable with respect to strong decays.
Inevitable Pentaquark Diakonov, Dmitri
Progress of theoretical physics. Supplement,
01/2007, Letnik:
168
Journal Article
Recenzirano
Odprti dostop
The experimental status of the pentaquark searches is briefly reviewed. Recent null results by the CLAS collaboration are commented, and new strong evidence of a very narrow Θ+ resonance by the DIANA ...collaboration is presented. On the theory side, we revisit the argument against the existence of the pentaquark – that of Callan and Klebanov – and show that actually a strong resonance is predicted in that approach, however its width is grossly overestimated. A recent calculation gives 2 MeV for the pentaquark width, and this number is probably still an upper bound.
The existence of a light
S
=
+
1
baryon resonance follows from Quantum Field Theory applied to baryons. This is illustrated in the Skyrme model (where
Θ
+
exists but is too strong) and in a new mean ...field approach where
Θ
+
arises as a consequence of three known resonances:
Λ
(
1405
)
,
N
(
1440
)
and
N
(
1535
)
.
We present a generating functional producing quark wave functions of all Fock states in the octet, decuplet and antidecuplet baryons in the mean field approximation, both in the rest and infinite ...momentum frames. In particular, for the usual octet and decuplet baryons we get the SU(6)‐symmetric wave functions for their 3‐quark component but with specific corrections from relativism and from additional quark‐antiquark pairs. For the exotic antidecuplet baryons we obtain the 5‐quark wave function.
A
bstract
C-parity-even quarkonia
η
b
,
c
and
χ
b,c
with spin 0 and 2 are produced via two-gluon fusion. The expected cross section of the inclusive production of the quarkonia at the LHC, times the ...branching ratios of convenient decays, is up to tens of nanobarn per unit rapidity in the case of charmonia and around one nanobarn for the bottomonia. Measuring the quarkonia production as function of rapidity will allow to determine the gluon distribution function in nucleons in a very broad range of the Bjorken
x
from
x
~ 10
−2
where it is already known, down to
x
~ 10
−6
where it is totally unknown. The scale of the gluon distribution found from such measurements turns out to be rather low,
Q
2
≃ 2
.
5 − 3 GeV
2
, for charmonia and rather large,
Q
2
≃ 20 GeV
2
, for bottomonia. We evaluate the scale by studying the next-to-leading-order production cross sections.
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