992 research outputs found
Static quark-antiquark potential and Dirac eigenvector correlators
We represent the Polyakov loop correlator as a spectral sum of correlators of
eigenvectors of the lattice Dirac operator. This spectral representation is
studied numerically using quenched SU(3) configurations below and above the
deconfinement temperature. We analyze whether the individual Dirac eigenvector
correlators differ in the confined and deconfined phases. The decay properties
of the normalized Dirac eigenvector correlators turn out to be essentially
identical in the two phases, but the amplitudes change. This change of the
amplitudes shifts the relative contributions of the individual Dirac
eigenvector correlators and is the driving mechanism for the transition from
the confining static potential into the deconfining one
Heavy Quark diffusion from lattice QCD spectral functions
We analyze the low frequency part of charmonium spectral functions on large
lattices close to the continuum limit in the temperature region as well as for . We present evidence for the
existence of a transport peak above and its absence below . The
heavy quark diffusion constant is then estimated using the Kubo formula. As
part of the calculation we also determine the temperature dependence of the
signature for the charmonium bound state in the spectral function and discuss
the fate of charmonium states in the hot medium.Comment: 4 pages, Proceedings for Quark Matter 2011 Conference, May 23-28,
2011, Annecy, Franc
Direct comparison of sterile neutrino constraints from cosmological data, <i>ν</i><sub><i>e</i></sub> disappearance data and <i>ν</i><sub><i>μ</i></sub>→ <i>ν</i><sub><i>e</i></sub> appearance data in a 3+1 model
A Novel Electrical Method to Measure Wire Tensions for Time Projection Chambers
We present a novel electrical technique to measure the tension of wires in
multi-wire drift chambers. We create alternating electric fields by biasing
adjacent wires on both sides of a test wire with a superposition of positive
and negative DC voltages on an AC signal (). The
resulting oscillations of the wire will display a resonance at its natural
frequency, and the corresponding change of the capacitance will lead to a
measurable current. This scheme is scalable to multiple wires and therefore
enables us to precisely measure the tension of a large number of wires in a
short time. This technique can also be applied at cryogenic temperatures making
it an attractive solution for future large time-projection chambers such as the
DUNE detector. We present the concept, an example implementation and its
performance in a real-world scenario and discuss the limitations of the
sensitivity of the system in terms of voltage and wire length.Comment: 7 pages, 8 figures. Accepted by NIM
Studies for a Photon Collider at the ILC
One option at the International Linear Collider is to convert the electron
beams into high energy photon beams by Compton scattering a few millimetres in
front of the interaction region. Selected physics channels for this option have
been analysed and technical issues have been studied. So far no showstoppers
for this option have been found.Comment: V2: Minor changes, accepted by NI
Strong Coupling Constant from the Photon Structure Function
We extract the value of the strong coupling constant alpha_s from a
single-parameter pointlike fit to the photon structure function F_2^gamma at
large x and Q^2 and from a first five-parameter full (pointlike and hadronic)
fit to the complete F_2^gamma data set taken at PETRA, TRISTAN, and LEP. In
next-to-leading order and the MSbar renormalization and factorization schemes,
we obtain alpha_s(m_Z)=0.1183 +/- 0.0050(exp.)^+0.0029_-0.0028(theor.)
[pointlike] and alpha_s(m_Z)=0.1198 +/- 0.0028(exp.)^+0.0034_-0.0046(theor.)
[pointlike and hadronic]. We demonstrate that the data taken at LEP have
reduced the experimental error by about a factor of two, so that a competitive
determination of alpha_s from F_2^gamma is now possible.Comment: 11 pages, 2 tables, 2 figures. Version accepted for publication by
Phys. Rev. Let
Gamma(*)Gamma(*) reaction at high energies
The energy available for gamma(*)gamma(*) physics at LEP2 is opening a new
window on the study of diffractive phenomena, both non-perturbative and
perturbative. We discuss some of the uncertainties and problems connected with
the experimental measurements and their interpretation.Comment: 6 pages, 6 figures, submitted to proceedings of the Durham Collider
Workshop, 22-26 September 199
Adjoint quarks and fermionic boundary conditions
We study quenched SU(2) lattice gauge theory with adjoint fermions in a wide
range of temperatures. We focus on spectral quantities of the Dirac operator
and use the temporal fermionic boundary conditions as a tool to probe the
system. We determine the deconfinement temperature through the Polyakov loop,
and the chiral symmetry restoration temperature for adjoint fermions through
the gap in the Dirac spectrum. This chiral transition temperature is about four
times larger than the deconfinement temperature. In between the two transitions
we find that the system is characterized by a non-vanishing chiral condensate
which differs for periodic and anti-periodic fermion boundary conditions. Only
for the latter (physical) boundary conditions, the condensate vanishes at the
chiral transition. The behavior between the two transitions suggests that
deconfinement manifests itself as the onset of a dependence of spectral
quantities of the Dirac operator on boundary conditions. This picture is
supported further by our results for the dual chiral condensate.Comment: Minor changes; final version to appear in JHE
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