3,542 research outputs found
Remarks on the Heavy Quark Potential in the Supergravity Approach
We point out certain unexpected features of the planar QCD3 confining
potential, as computed from a classical worldsheet action in an AdS metric via
the Maldacena conjecture. We show that there is no Luscher c/R term in the
static-quark potential, which is contrary to both the prediction of various
effective string models, and the results of some recent lattice Monte Carlo
studies. It is also noted that the glueball masses extracted from classical
supergravity tend to finite, coupling-independent constants in the strong
coupling limit, even as the string tension tends to infinity in the same limit;
this is a counter-intuitive result.Comment: 10 pages, 2 figures, Latex2e. Some additional remarks added
concerning worldsheet fluctuations in AdS spac
Worldsheet Fluctuations and the Heavy Quark Potential in the AdS/CFT Approach
We consider contributions to the heavy quark potential, in the AdS/CFT approach to SU(N) gauge theory, which arise from first order fluctuations of the associated worldsheet in anti-deSitter space. The gaussian fluctuations occur around a classical worldsheet configuration resembling an infinite square well, with the bottom of the well lying at the AdS horizon. The eigenvalues of the corresponding Laplacian operators can be shown numerically to be very close to those in flat space. We find that two of the transverse world sheet fields become massive, which may have implications for the existence of a L{ĂĽ}scher term in the heavy quark potential. It is also suggested that these massive degrees of freedom may relate to extrinsic curvature of the QCD string
Broadening of the QCD3 flux tube from the AdS/CFT correspondence
We use the finite temperature AdS/CFT approach to demonstrate logarithmic
broadening of the confining QCD3 flux tube as a function of quark separation.
This behavior indicates that, unlike lattice QCD, there is no roughening
transition in the AdS/CFT formulation, which raises the interesting possibility
of extrapolating strong coupling results to weak couplings by the use of
resummation techniques. In the zero-temperature non-confining limit, we find
that this logarithmic broadening of the field strength distribution is absent.
Our results are obtained numerically at strong couplings, in the supergravity
approximation.Comment: 19 pages, LaTex, 10 figures. Version to appear in JHE
From the Quantum Link Model on the Honeycomb Lattice to the Quantum Dimer Model on the Kagom\'e Lattice: Phase Transition and Fractionalized Flux Strings
We consider the -d quantum link model on the honeycomb lattice
and show that it is equivalent to a quantum dimer model on the Kagom\'e
lattice. The model has crystalline confined phases with spontaneously broken
translation invariance associated with pinwheel order, which is investigated
with either a Metropolis or an efficient cluster algorithm. External
half-integer non-Abelian charges (which transform non-trivially under the
center of the gauge group) are confined to each other
by fractionalized strings with a delocalized flux. The strands
of the fractionalized flux strings are domain walls that separate distinct
pinwheel phases. A second-order phase transition in the 3-d Ising universality
class separates two confining phases; one with correlated pinwheel
orientations, and the other with uncorrelated pinwheel orientations.Comment: 16 pages, 20 figures, 2 tables, two more relevant references and one
short paragraph are adde
From the Quantum Link Model on the Honeycomb Lattice to the Quantum Dimer Model on the Kagom\'e Lattice: Phase Transition and Fractionalized Flux Strings
We consider the -d quantum link model on the honeycomb lattice
and show that it is equivalent to a quantum dimer model on the Kagom\'e
lattice. The model has crystalline confined phases with spontaneously broken
translation invariance associated with pinwheel order, which is investigated
with either a Metropolis or an efficient cluster algorithm. External
half-integer non-Abelian charges (which transform non-trivially under the
center of the gauge group) are confined to each other
by fractionalized strings with a delocalized flux. The strands
of the fractionalized flux strings are domain walls that separate distinct
pinwheel phases. A second-order phase transition in the 3-d Ising universality
class separates two confining phases; one with correlated pinwheel
orientations, and the other with uncorrelated pinwheel orientations.Comment: 16 pages, 20 figures, 2 tables, two more relevant references and one
short paragraph are adde
Confinement effects from interacting chromo-magnetic and axion fields
We study a non-Abelian gauge theory with a pseudo scalar coupling \phi
\epsilon ^{\mu \nu \alpha \beta} F_{\mu \nu}^a F_{\alpha \beta}^a in the case
where a constant chromo-electric, or chromo-magnetic, strength expectation
value is present. We compute the interaction potential within the framework of
gauge-invariant, path-dependent, variables formalism. While in the case of a
constant chromo-electric field strength expectation value the static potential
remains Coulombic, in the case of a constant chromo-magnetic field strength the
potential energy is the sum of a Coulombic and a linear potentials, leading to
the confinement of static charges.Comment: 12 pages, no figures, published versio
Quantum corrections from a path integral over reparametrizations
We study the path integral over reparametrizations that has been proposed as
an ansatz for the Wilson loops in the large- QCD and reproduces the area law
in the classical limit of large loops. We show that a semiclassical expansion
for a rectangular loop captures the L\"uscher term associated with
dimensions and propose a modification of the ansatz which reproduces the
L\"uscher term in other dimensions, which is observed in lattice QCD. We repeat
the calculation for an outstretched ellipse advocating the emergence of an
analog of the L\"uscher term and verify this result by a direct computation of
the determinant of the Laplace operator and the conformal anomaly
Wilson Loops and QCD/String Scattering Amplitudes
We generalize modern ideas about the duality between Wilson loops and
scattering amplitudes in SYM to large QCD by deriving a
general relation between QCD meson scattering amplitudes and Wilson loops. We
then investigate properties of the open-string disk amplitude integrated over
reparametrizations. When the Wilson loop is approximated by the area behavior,
we find that the QCD scattering amplitude is a convolution of the standard
Koba-Nielsen integrand and a kernel. As usual poles originate from the first
factor, whereas no (momentum dependent) poles can arise from the kernel. We
show that the kernel becomes a constant when the number of external particles
becomes large. The usual Veneziano amplitude then emerges in the kinematical
regime where the Wilson loop can be reliably approximated by the area behavior.
In this case we obtain a direct duality between Wilson loops and scattering
amplitudes when spatial variables and momenta are interchanged, in analogy with
the =4 SYM case.Comment: 39pp., Latex, no figures; v2: typos corrected; v3: final, to appear
in PR
Integrated nitrogen input systems in Denmark
Cycling of N in agriculture through the use of mineral fertilizers, manures and N-fixing crops gives rise to many forms of N emissions to the environment, including nitrate (NO3) leaching, ammonia (NH3) volatilization and nitrous oxide (N2O) emissions, resulting in ground water pollution, eutrophication of surface waters, soil acidification and contributions to global warming. The high rates of N input in intensive North European agricultural systems have given rise to high loss rates, and the focus in Danish agriculture during the past two decades has been on increasing the N use efficiency with the aim of reducing losses. The N use efficiency at the system level can be increased by improved handling of manure, targeted application of fertilizers and manures, and through adjustments of the crop rotation
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