588 research outputs found
QCD sum rules for D mesons in dense and hot nuclear matter
Open charm mesons (pseudo-scalar and scalar as well as axial-vector and
vector) propagating or resting in nuclear matter display an enhanced
sensitivity to the chiral condensate. This offers new prospects to seek for
signals of chiral restoration, in particular in p-A and p-bar-A reactions as
envisaged in first-round experiments by the CBM and PANDA collaborations at
FAIR. Weinberg type sum rules for charming chiral partners are presented, and
the distinct in-medium modifications of open-charm mesons are discussed. We
also address the gluon condensates near Tc and their impact on QCD sum rules.Comment: 6 pages, 7 figures, conference proceeding
QCD sum rules for D and B mesons in nuclear matter
QCD sum rules for D and B mesons embedded in cold nuclear matter are
evaluated. We quantify the mass splitting of D - D-bar and B - B-bar mesons as
a function of the nuclear matter density; extrapolated to saturation density it
is in the order of 60 and 130 MeV driven essentially by the condensates
, and . The genuine chiral
condensate , amplified by heavy-quark masses, enters the Borel
transformed sum rules for the mass splitting beyond linear density dependence.
Including strange quark condensates reveals a umerically smaller and opposite
effect for the Ds - Ds-bar mass splitting.Comment: 16 pages, 8 figures, to be published; a broader range of condensate
values is discussed (v2
Spectral caustics in laser assisted Breit-Wheeler process
Electron-positron pair production by the Breit-Wheeler process embedded in a
strong laser pulse is analyzed. The transverse momentum spectrum displays
prominent peaks which are interpreted as caustics, the positions of which are
accessible by the stationary phases. Examples are given for the superposition
of an XFEL beam with an optical high-intensity laser beam. Such a configuration
is available, e.g., at LCLS at present and at European XFEL in near future. It
requires a counter propagating probe photon beam with high energy which can be
generated by synchronized inverse Compton backscattering
In-Medium Modifications of Scalar Charm Mesons in Nuclear Matter
Employing QCD sum rules the in-medium modifications of scalar charm mesons in
a cold nuclear matter environment are estimated. The mass splitting of
D*-D*-bar is quantified.Comment: Talk given at QCD 10, Montpelier, France, 27.06.-05.07.201
Thermodynamics of the \phi^4 theory in tadpole approximation
Relying on the Luttinger-Ward theorem we derive a thermodynamically
selfconsistent and scale independent approximation of the thermodynamic
potential for the scalar theory in the tadpole approximation. The
resulting thermodynamic potential as a function of the temperature is similar
to the one of the recently proposed screened perturbation theory.Comment: 6 pages, including 1 eps figur
Four-quark condensates in open-charm chiral QCD sum rules
Recently, in Hilger et al. (2011) [1] QCD sum rules for chiral partners in
the open-charm meson sector have been presented at nonzero baryon net density
or temperature up to and including mass dimension 5. Referring to this, details
concerning the cancelation of infrared divergences are presented and important
technical and conceptional ingredients for an incorporation of four-quark
condensates beyond factorization and of other mass dimension 6 condensates are
collected.Comment: 7 pages, 5 figures, conference proceedin
Chiral QCD sum rules for open charm mesons
QCD sum rules for chiral partners in the open-charm meson sector are
presented at nonzero baryon net density or temperature. We focus on the
differences between pseudo-scalar and scalar as well as vector and axial-vector
D mesons and derive the corresponding Weinberg type sum rules. This allows for
the identification of such QCD condensates which drive the non-degeneracy of
chiral partners in lowest order of the strong coupling alpha_s and which
therefore may serve as "order parameters" for chiral restoration (or elements
thereof).Comment: 24 pages, 4 figure
Pair production by Schwinger and Breit-Wheeler processes in bi-frequent fields
Counter-propagating and suitably polarized light (laser) beams can provide
conditions for pair production. Here, we consider in more detail the following
two situations: (i) In the homogeneity regions of anti-nodes of linearly
polarized ultra-high intensity laser beams, the Schwinger process is
dynamically assisted by a second high-frequency field, e.g. by a XFEL beam.
(ii) A high-energy probe photon beam colliding with a superposition of
co-propagating intense laser and XFEL beams gives rise to the laser assisted
Breit-Wheeler process. Prospects of such bi-frequent field constellations with
respect to the feasibility of conversion of light into matter are discussed
Microscopic Model versus Systematic Low-Energy Effective Field Theory for a Doped Quantum Ferromagnet
We consider a microscopic model for a doped quantum ferromagnet as a test
case for the systematic low-energy effective field theory for magnons and
holes, which is constructed in complete analogy to the case of quantum
antiferromagnets. In contrast to antiferromagnets, for which the effective
field theory approach can be tested only numerically, in the ferromagnetic case
both the microscopic and the effective theory can be solved analytically. In
this way the low-energy parameters of the effective theory are determined
exactly by matching to the underlying microscopic model. The low-energy
behavior at half-filling as well as in the single- and two-hole sectors is
described exactly by the systematic low-energy effective field theory. In
particular, for weakly bound two-hole states the effective field theory even
works beyond perturbation theory. This lends strong support to the quantitative
success of the systematic low-energy effective field theory method not only in
the ferromagnetic but also in the physically most interesting antiferromagnetic
case.Comment: 34 pages, 1 figur
Systematic Low-Energy Effective Field Theory for Magnons and Holes in an Antiferromagnet on the Honeycomb Lattice
Based on a symmetry analysis of the microscopic Hubbard and t-J models, a
systematic low-energy effective field theory is constructed for hole-doped
antiferromagnets on the honeycomb lattice. In the antiferromagnetic phase,
doped holes are massive due to the spontaneous breakdown of the
symmetry, just as nucleons in QCD pick up their mass from spontaneous chiral
symmetry breaking. In the broken phase the effective action contains a
single-derivative term, similar to the Shraiman-Siggia term in the square
lattice case. Interestingly, an accidental continuous spatial rotation symmetry
arises at leading order. As an application of the effective field theory we
consider one-magnon exchange between two holes and the formation of two-hole
bound states. As an unambiguous prediction of the effective theory, the wave
function for the ground state of two holes bound by magnon exchange exhibits
-wave symmetry.Comment: 33 pages, 6 figure
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