91 research outputs found
Integral equation for gauge invariant quark Green's function
We consider gauge invariant quark two-point Green's functions in which the
gluonic phase factor follows a skew-polygonal line. Using a particular
representation for the quark propagator in the presence of an external gluon
field, functional relations between Green's functions with different numbers of
segments of the polygonal lines are established. An integral equation is
obtained for the Green's function having a phase factor along a single straight
line. The related kernels involve Wilson loops with skew-polygonal contours and
with functional derivatives along the sides of the contours.Comment: 7 pages; talk given at the Joint Meeting
Heidelberg-Liege-Paris-Wroclaw, Spa, 6-8 March 2008; to appear in the
Proceedings (AIP
Forward Physics at the LHC: within and beyond the Standard Model
We review the detection capabilities in the forward direction of the various
LHC experiments together with the associated physics programme. A selection of
measurements accessible with near-beam instrumentation in various sectors (and
extensions) of the Standard Model (SM) is outlined, including QCD (diffractive
and elastic scattering, low-x parton dynamics, hadronic Monte Carlos for
cosmic-rays), electroweak processes in gamma-gamma interactions, and Higgs
physics (vector-boson-fusion and central exclusive production).Comment: 9 pages, 18 figs. Lectures given at the LAWHEP'07 School (Sao Miguel
das Missoes, Brazil, 3-7 Dec 2007) to appear in Braz. J. Phys. Also presented
in HLPW08 (Spa, Belgium, 6-8 Mar 2008) AIP Conf. Proceeds, to appear; and in
HANUC European Grad. School (Jyvaskyla, Finland, 25-29 Aug. 2008
[56,4(+)] baryons in the 1/N-c expansion
Using the 1/N-c expansion of QCD, we analyze the spectrum of positive parity resonances with strangeness S=0, -1, -2, and -3 in the 2-3 GeV mass region, supposed to belong to the [56,4(+)] multiplet. The mass operator is similar to that of [56,2(+)], previously studied in the literature. The analysis of the latter is revisited. In the [56,4(+)] multiplet we find that the spin-spin term brings the dominant contribution and that the spin-orbit term is entirely negligible in the hyperfine interaction, in agreement with constituent quark model results. More data are strongly desirable, especially in the strange sector in order to fully exploit the power of this approach
The charge conjugation quantum number in multiquark systems
We discuss the charge conjugation quantum number for tetraquarks or
meson-meson molecules, seen as possible interpretations of the newly found
charmonium-like resonances.Comment: 7 pages, 1 figure, based on a talk given at the Joint Meeting
Heidelberg-Liege-Paris-Wroclaw (HLPW08): Three Days of Strong Interactions
and Astrophysics, Spa, March 6-8, 2008, Eqs. (18)-(25) corrected, text
slightly polished, conclusions unchange
Core-collapse supernova neutrinos and neutrino properties
Core-collapse supernovae are powerful neutrino sources. The observation of a
future (extra-)galactic supernova explosion or of the relic supernova neutrinos
might provide important information on the supernova dynamics, on the supernova
formation rate and on neutrino properties. One might learn more about unknown
neutrino properties either from indirect effects in the supernova (e.g. on the
explosion or on in the r-process) or from modifications of the neutrino time or
energy distributions in a detector on Earth. Here we will discuss in particular
possible effects of CP violation in the lepton sector. We will also mention the
interest of future neutrino-nucleus interaction measurements for the precise
knowledge of supernova neutrino detector response to electron neutrinos.Comment: 9 pages, 5 figures, Proceedings to "Three days of Strong Interactions
& Astrophysics HLPW08", 6-8 March 2008, SP
Group Theoretical Analysis of the Wave Function of the Nonstrange Baryons in the Expansion
Using standard group theoretical techniques we construct the exact wave
function of the multiplet in the orbital, spin and flavor
space. This symmetric wave function is compared to that customarily used in the
expansion, which is asymmetric. The comparison is made by analyzing the
matrix elements of various operators entering the mass formula. These matrix
elements are calculated by the help of isoscalar factors of the permutation
group, specially derived for this purpose as a function of . We also
compare two distinct methods used in the study of the
multiplet. In the first method the generators are divided into two parts, one
part acting on a subsystem of quarks called core and another on the
separated quark. In the second method the system is treated as a whole. We show
that the latter is simpler and allows to clearly reveal the physically
important operators in the mass formula.Comment: 14 pages, 12 tables, talk given by N. Matagne at the workshop "Three
Days of Strong Interactions and Astrophysics", joint meeting
Heidelberg-Liege-Paris-Wroclaw, March 6-8, 2008, Sol Cress, Spa, Belgium,to
be published in AIP Proceeding
Two-photon decay of pseudoscalar quarkonia
We report on our recent evaluation of the two-photon width of the
pseudoscalar quarkonia, eta_c(nS) and eta_b(nS) in an approach based on
Heavy-Quark Spin Symmetry (HQSS). To what concerns the 1S state eta_c, our
parameter-free computation agrees with experiments, as well as most of other
theoretical works. On the other hand, our computation for the 2S-state looks 2S
like a confirmation that there may exist an anomaly related to the decay of
eta_c(2S), especially in the light of the new preliminary result of the Belle
collaboration. We also point out that the essentially model-independent ratio
of eta_b two-photon width to the Upsilon leptonic width and the eta_b
two-photon width could be used to extract the strong coupling constant alpha_s.Comment: Presented by T.N. Pham at the Joint Meeting
Heidelberg-Liege-Paris-Wroclaw (HLPW08), Spa, Belgium, 6-8 March 2008, 9
pages, 2 figures, LaTeX, uses aip-6s.clo, aipproc.cls and aipxfm.sty
(included
Pions in the quark matter phase diagram
The relationship between mesonic correlations and quantum condensates in the
quark matter phase diagram is explored within a quantum field theoretical
approach of the Nambu and Jona-Lasinio (NJL) type. Mean-field values in the
scalar meson and diquark channels are order parameters signalling the
occurrence of quark condensates, entailing chiral symmetry breaking (chi SB)
and color superconductivity (2SC) in quark matter. We investigate the spectral
properties of scalar and pseudoscalar meson excitations in the phase diagram in
Gaussian approximation and show that outside the chi SB region where the pion
is a zero-width bound state, there are two regions where it can be considered
as a quasi-bound state with a lifetime exceeding that of a typical heavy-ion
collision fireball: (A) the high-temperature chi SB crossover region at low
densities and (B) the high-density color superconducting phase at temperatures
below 100 MeV.Comment: presented by D. Zablocki at the Joint Meeting
Heidelberg-Liege-Paris-Wroclaw (HLPW08), Spa, Belgium, 6-8 March 2008, 10
pages, 5 figures, LaTeX, uses aip-6s.clo, aipproc.cls and aipxfm.sty
(included
Axions and polarisation of quasars
We present results showing that, thanks to axion-photon mixing in external
magnetic fields, it is actually possible to produce an effect similar to the
one needed to explain the large-scale coherent orientations of quasar
polarisation vectors in visible light that have been observed in some regions
of the sky.Comment: Contributed to "Three days of Strong Interactions & Astrophysics,
Heidelberg-Liege-Paris-Wroclaw", 6/3/2008-8/3/2008, Spa, Belgium. To be
published in AIP proceeding
Astrophysical tests of mirror dark matter
Mirror matter is a self-collisional dark matter candidate. If exact mirror
parity is a conserved symmetry of the nature, there could exist a parallel
hidden (mirror) sector of the Universe which has the same kind of particles and
the same physical laws of our (visible) sector. The two sectors interact each
other only via gravity, therefore mirror matter is naturally "dark". The most
promising way to test this dark matter candidate is to look at its
astrophysical signatures, as Big Bang nucleosynthesis, primordial structure
formation and evolution, cosmic microwave background and large scale structure
power spectra.Comment: 9 pages, 2 figure
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