64 research outputs found
Electromagnetic superconductivity of vacuum induced by strong magnetic field: numerical evidence in lattice gauge theory
Using numerical simulations of quenched SU(2) gauge theory we demonstrate
that an external magnetic field leads to spontaneous generation of quark
condensates with quantum numbers of electrically charged rho mesons if the
strength of the magnetic field exceeds the critical value eBc = 0.927(77) GeV^2
or Bc =(1.56 \pm 0.13) 10^{16} Tesla. The condensation of the charged rho
mesons in strong magnetic field is a key feature of the magnetic-field-induced
electromagnetic superconductivity of the vacuum.Comment: 14 pages, 5 figures, 2 tables, elsarticle style; continuum limit is
analyzed, best fit parameters are presented in Table 2, published versio
Dispersionless Toda hierarchy and two-dimensional string theory
The dispersionless Toda hierarchy turns out to lie in the heart of a recently
proposed Landau-Ginzburg formulation of two-dimensional string theory at
self-dual compactification radius. The dynamics of massless tachyons with
discrete momenta is shown to be encoded into the structure of a special
solution of this integrable hierarchy. This solution is obtained by solving a
Riemann-Hilbert problem. Equivalence to the tachyon dynamics is proven by
deriving recursion relations of tachyon correlation functions in the machinery
of the dispersionless Toda hierarchy. Fundamental ingredients of the
Landau-Ginzburg formulation, such as Landau-Ginzburg potentials and tachyon
Landau-Ginzburg fields, are translated into the language of the Lax formalism.
Furthermore, a wedge algebra is pointed out to exist behind the Riemann-Hilbert
problem, and speculations on its possible role as generators of ``extra''
states and fields are presented.Comment: LaTeX 21 pages, KUCP-0067 (typos are corrected and a brief note is
added
Renormalization group improvement of the spectrum of Hydrogen-like atoms with massless fermions
We obtain the next-to-next-to-leading-log renormalization group improvement
of the spectrum of Hydrogen-like atoms with massless fermions by using
potential NRQED. These results can also be applied to the computation of the
muonic Hydrogen spectrum where we are able to reproduce some known double logs
at O(m\alpha^6). We compare with other formalisms dealing with log resummation
available in the literature.Comment: 9 pages, LaTeX. Minor changes, note added, final versio
Space-time evolution of hadronization
Beside its intrinsic interest for the insights it can give into color
confinement, knowledge of the space-time evolution of hadronization is very
important for correctly interpreting jet-quenching data in heavy ion collisions
and extracting the properties of the produced medium. On the experimental side,
the cleanest environment to study the space-time evolution of hadronization is
semi-inclusive Deeply Inelastic Scattering on nuclear targets. On the
theoretical side, 2 frameworks are presently competing to explain the observed
attenuation of hadron production: quark energy loss (with hadron formation
outside the nucleus) and nuclear absorption (with hadronization starting inside
the nucleus). I discuss recent observables and ideas which will help to
distinguish these 2 mechanisms and to measure the time scales of the
hadronization process.Comment: 6 pages, 4 figures. Based on talks given at "Hot Quarks 2006",
Villasimius, Italy, May 15-20, 2006, and at the "XLIV internataional winter
meeting on nuclear physics", Bormio, Italy, Jan 29 - Feb 5, 2006. To appear
in Eur.Phys.J.
Renormalization group improvement of the NRQCD Lagrangian and heavy quarkonium spectrum
We complete the leading-log renormalization group scaling of the NRQCD
Lagrangian at . The next-to-next-to-leading-log renormalization group
scaling of the potential NRQCD Lagrangian (as far as the singlet is concerned)
is also obtained in the situation . As a
by-product, we obtain the heavy quarkonium spectrum with the same accuracy in
the situation m\alpha_s^2 \simg \Lambda_{QCD}. When , this is equivalent to obtain the whole set of
terms in the heavy quarkonium spectrum.
The implications of our results in the non-perturbative situation are also mentioned.Comment: 16 pages, LaTeX. Minor changes. Final versio
Optimalisatie bemesting: Een blauwdruk voor optimaal hergebruik van drainwater getoetst op vijf bedrijven
Het doel van dit onderzoek is het beperken van de uitstoot van overtollig drainwater naar het milieu door beter beheersen van de water- en voedingsstromen binnen het bedrijf. Een kerngedachte hierbij is dat de emissie kan verminderen door de samenstelling van de gift zo goed mogelijk aan te passen aan de behoefte van het gewas. Op vijf bedrijven is gekeken naar de water- en voedingshuishouding. Op basis van bestaande gegevens is per bedrijf en per dag berekend wat het verschil is tussen gift en drain uitgedrukt in l.m -2 (voor water) en in mmol.m -2 (voor de afzonderlijke voedingselementen) Hierbij is het verschil plantbehoefte genoemd hoewel daar andere verliezen bij ingesloten zij
Renormalization group analysis of the QCD quark potential to order v^2
A one-loop renormalization group analysis of the order v^2 relativistic
corrections to the static QCD potential is presented. The velocity
renormalization group is used to simultaneously sum ln(m/mv) and ln(m/mv^2)
terms. The results are compared to previous calculations in the literature.Comment: 13 pages. important change: running of soft Lagrangian include
The QCD heavy-quark potential to order v^2: one loop matching conditions
The one-loop QCD heavy quark potential is computed to order v^2 in the color
singlet and octet channels. Several errors in the previous literature are
corrected. To be consistent with the velocity power counting, the full
dependence on |p' + p|/|p' - p| is kept. The matching conditions for the NRQCD
one-loop potential are computed by comparing the QCD calculation with that in
the effective theory. The graphs in the effective theory are also compared to
terms from the hard, soft, potential, and ultrasoft regimes in the threshold
expansion. The issue of off-shell versus on-shell matching and gauge dependence
is discussed in detail for the 1/(m k) term in the potential. Matching on-shell
gives a 1/(m k) potential that is gauge independent and does not vanish for
QED.Comment: 28 pages, References added and minor changes to section III, results
unchange
Doseersysteem voor element correcties: Aanpassingen in ammonium en calcium gift, gebaseerd op pH en ammoniumvracht
De werking is getest van een flexibel geautomatiseerd meet- en regelsysteem voor de ammoniumgift (afhankelijk van de pH van de drain). Het effect is van de verhoogde ammoniumgift op de pH, de gewassamenstelling en gewasproductie is gemeten
The Isgur-Wise function in a relativistic model for system
We use the Dirac equation with a ``(asymptotically free) Coulomb + (Lorentz
scalar) linear '' potential to estimate the light quark wavefunction for mesons in the limit . We use these wavefunctions to
calculate the Isgur-Wise function for orbital and radial
ground states in the phenomenologically interesting range . We find a simple expression for the zero-recoil slope, , where is the energy eigenvalue
of the light quark, which can be identified with the parameter
of the Heavy Quark Effective Theory. This result implies an upper bound of
for the slope . Also, because for a very light quark the size of the meson is determined mainly by the
``confining'' term in the potential , the shape of
is seen to be mostly sensitive to the dimensionless
ratio . We present results for the ranges of
parameters , and
light quark masses and compare to existing
experimental data and other theoretical estimates. Fits to the data give:
,
and [ARGUS
'93]; , and
[CLEO '93]; ${\bar\Lambda_{u,d}}^2/Comment: 22 pages, Latex, 4 figures (not included) available by fax or via
email upon reques
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