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2.
We derive a method to calculate the multi-channel K -matrix applicable to a broad class of models in which mesons linearly couple to the quark core. The method is used to calculate
pion scattering amplitudes in the energy region of low-lying P11 and P33 resonances. A good agreement with experimental data
is achieved if in addition to the elastic channel we include the
and
N (
channels where the -meson models the correlated two-pion decay. We solve the integral equation for the K -matrix in the approximation of separable kernels; it yields a sizable increase of the widths of the (1232) and the N(1440) resonances compared to the bare quark values. 相似文献
3.
G. Martens C. Greiner S. Leupold U. Mosel 《The European Physical Journal A - Hadrons and Nuclei》2003,18(2-3):223-226
We calculate color electric fields of quark/antiquark (
) and 3-quark (qqq) systems within the Chromodielectric Model (CDM). We explicitly evaluate the string tension of flux tubes in the
-system and analyze their profile. To reproduce results of lattice calculations we use a bag pressure
from which an effective strong-coupling constant
follows. With these parameters we get a Y-shaped configuration for large qqq-systems.Received: 30 September 2002, Published online: 22 October 2003PACS:
11.10.Lm Field theory: Nonlinear or nonlocal theories and models - 11.15.Kc Gauge field theories: Classical and semiclassical techniques - 12.39.Ba Phenomenological quark models: Bag model 相似文献
4.
F. Farchioni I. Montvay E. Scholz L. Scorzato The qq+q Collaboration 《The European Physical Journal C - Particles and Fields》2003,31(2):227-238
The dependence of the pseudo-scalar meson masses and decay constants on sea and valence quark masses is compared to next-to-leading order (NLO) chiral perturbation theory (ChPT). The numerical simulations with two light dynamical quark flavors are performed with the Wilson quark lattice action at gauge coupling
and hopping parameters
on a 164 lattice.
lattice artifacts are taken into account by applying chiral perturbation theory for the Wilson lattice action. The values of the relevant combinations of Gasser-Leutwyler constants L
4, L
5, L
6 and L
8 are estimated.Received: 7 July 2003, Published online: 2 October 2003 相似文献
5.
The qq+q Collaboration F. Farchioni I. Montvay E. Scholz 《The European Physical Journal C - Particles and Fields》2004,37(2):197-204
Our previous calculations of the sea- and valence-quark mass dependence of the pseudoscalar meson masses and decay constants is repeated on a
lattice, which allows for a better determination of the quantities in question. The conclusions are similar as before on the 164 lattice [1]. The two light dynamical quark flavours we simulate have masses in the range m
s
/4 < m
u,d
< 2m
s
/3. The sea quark mass dependence of
and
is well described by the next-to-leading order (NLO) chiral perturbation theory (ChPT) formulas and clearly shows the presence of chiral logarithms. The valence quark mass dependence requires the presence of NNLO contributions in partially quenched ChPT (PQChPT)--in addition to the NLO terms. The
lattice artifacts in these quantities turn out to be small.Received: 19 March 2004, Published online: 24 August 2004 相似文献
6.
The nonlocal version of the SU(2) x SU(2) symmetric four-quark interaction of the NJL type is considered. Each of the quark lines contains the form factors. These form factors remove the ultraviolet divergences in quark loops. The additional condition on the quark mass function m(p) ensures the absence of the poles in the quark propagator (quark confinement). The constituent-quark mass m(0) is expressed through the cut-off parameter
,
MeV in the chiral limit. These parameters are fixed by the experimental value of the weak pion decay and allow us to describe the mass of the light scalar meson, the strong decay
and the D/S ratio in the decay
in satisfactory agreement with the experimental data.Received: 16 June 2003, Revised: 28 July 2003, Published online: 18 December 2003PACS:
14.40.-n Mesons - 11.10.Lm Nonlinear or nonlocal theories and models - 12.39.Ki Relativistic quark model 相似文献
7.
A search for lepton-flavor-violating interactions
and
has been performed with the ZEUS detector using the entire HERA I data sample, corresponding to an integrated luminosity
of
. The data were taken at center-of-mass energies,
, of 300 and
. No evidence of lepton-flavor violation was found, and constraints were derived on leptoquarks (LQs) that could mediate such
interactions. For LQ masses below
, limits were set on
, where
is the coupling of the LQ to an electron and a first-generation quark q1, and
is the branching ratio of the LQ to the final-state lepton
(μ or
) and a quark q. For LQ masses much larger than
, limits were set on the four-fermion interaction term
for LQs that couple to an electron and a quark
and to a lepton
and a quark
, where
and
are quark generation indices. Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks
in R-Parity-violating supersymmetric models. In some cases, especially when a higher-generation quark is involved and for the
process
, the ZEUS limits are the most stringent to date.
Received: 1 April 2005, Revised: 13 July 2005, Published online: 18 October 2005 相似文献
8.
?nan? ?ahin 《The European Physical Journal C - Particles and Fields》2009,60(3):431-439
We investigate the potential of γ
γ collisions to probe scalar unparticle couplings via top–antitop quark pair production. We find 95% confidence level limits
on the unparticle couplings with an integrated luminosity of 500 fb−1 and an energy of
TeV. We investigate the effect of the top quark spin polarization on the unparticle couplings. It is shown that spin polarization
of the top quark leads to a significant improvement in the sensitivity limits. 相似文献
9.
G. S. Khadekar Rupali Wanjari Cenap Ozel 《International Journal of Theoretical Physics》2009,48(9):2550-2557
In this study we have analyzed the Kaluza-Klein type Robertson Walker (RW) cosmological model by considering variable cosmological
constant term Λ of the form:
,
and Λ∼ρ in the presence of strange quark matter with domain wall. The various physical aspects of the model are also discussed. 相似文献
10.
S. Descotes-Genon N. H. Fuchs L. Girlanda J. Stern 《The European Physical Journal C - Particles and Fields》2004,34(2):201-227
Due to its light mass, of order
, the strange quark can play a special role in chiral symmetry breaking (
SB): differences in the pattern of
SB in the limits Nf = 2 (
, ms physical) and Nf = 3 (
) may arise due to vacuum fluctuations of
pairs, related to the violation of the Zweig rule in the scalar sector and encoded in particular in the O(p4) low-energy constants L4 and L6. In case of large fluctuations, we show that the customary treatment of SU(3) x SU(3) chiral expansions generates instabilities upsetting their convergence. We develop a systematic program to cure these instabilities by resumming non-perturbatively vacuum fluctuations of
pairs, in order to extract information about
SB from experimental observations even in the presence of large fluctuations. We advocate a Bayesian framework for treating the uncertainties due to the higher orders. As an application, we present a three-flavor analysis of the low-energy
scattering and show that the recent experimental data imply a lower bound on the quark mass ratio
at 95% confidence level. We outline how additional information may be incorporated to further constrain the pattern of
SB in the Nf = 3 chiral limit.Received: 2 December 2003, Published online: 3 March 2004J. Stern: stern@ipno.in2p3.fr 相似文献
11.
S. Leupold 《The European Physical Journal A - Hadrons and Nuclei》2003,18(2-3):219-221
The properties of mesonic resonances can be calculated in terms of the low-energy coefficients of chiral perturbation theory (
PT) by extending unitarized
PT to higher energies. On the other hand, these low-energy coefficients can be calculated in two different models, namely i) by assuming resonance saturation and ii) within a constituent quark model. By matching the expressions of the two models combined with the results of unitarized
PT and the Weinberg sum rules, the properties of vector and axial-vector mesons can be calculated in the combined large-N
c
and chiral limit.Received: 30 September 2002, Published online: 22 October 2003PACS:
12.39.Fe Phenomenological quark models: Chiral Lagrangians - 14.40.Cs Properties of specific particles: Other mesons with S = C = 0, mass < 2.5 GeV 相似文献
12.
F. Arleo 《The European Physical Journal C - Particles and Fields》2003,30(2):213-221
The multiple scatterings incurred by a hard quark produced in a nuclear medium induce the emission of soft gluons which carry a fraction of the quark energy and eventually affect the hadronization process. Here, the depletion of semi-inclusive hadron spectra in DIS on various nuclei (N, Ne, Cu, Kr) is computed as a function of
and z to leading order in
through medium-modified fragmentation functions. Using the transport coefficient
previously determined from Drell-Yan production, the predictions are found to be in good agreement with EMC and HERMES preliminary data. Calculations on Xe targets are also presented and discussed.Received: 24 June 2003, Published online: 20 August 2003 相似文献
13.
The quark mass function
in QCD is revisited, using a gluon propagator in the form 1/(k
2 + m
g
2) plus
, where the second (IR) term gives linear confinement for m
g
= 0 in the instantaneous limit, being another scale. To find
we propose a new (differential) form of the Dyson-Schwinger equation (DSE) for
, based on an infinitesimal subtractive renormalization via a differential operator which lowers the degree of divergence in integration on the RHS, by two units. This warrants
in the integrand since its k-dependence is no longer sensitive to the principal term (p-k)2 in the quark propagator. The simplified DSE (which incorporates the Ward-Takahashi (WT) identity in the Landau gauge) is satisfied for large p
2 by
=
, except for Log factors. The limit p
2 = 0 determines
. A third limit, p
2 = -m
0
2, defines the dynamical mass m
0 via
. After two checks (
MeV and
=
), for
with
MeV, the T-dependent DSE is used in the real time formalism to determine the critical index
analytically, with the IR term partly serving as the H-field. We find
MeV and check the vanishing of
and
at T
c.Received: 31 August 2004, Published online: 11 January 2005PACS:
24.85. + p, 12.38.Lg, 12.38.AwA.N. Mitra: Permanent address: 244 Tagore Park, Delhi-110009, India. 相似文献
14.
Constraints on the whole spectrum of lepton flavor violating vertices are shown in the context of the standard two Higgs doublet model. The vertex involving the e-
mixing is much more constrained than the others, and the decays proportional to such a vertex are usually very suppressed. On the other hand, bounds on the quark sector are obtained from leptonic decays of the Bd,s0 mesons and from
. We emphasize that although the Bd0-
mixing restricts severely the d-b mixing vertex, the upper bound for this vertex could still give a sizable contribution to the decay
with respect to the standard model contribution, from which we see that such a vertex could still play a role in the phenomenology.Received: 16 September 2004, Published online: 26 April 2005PACS:
12.60.Fr, 12.15.Mm, 12.15.Ff, 11.30.Hv 相似文献
15.
We investigate the properties of qq and
states in hot and dense quark matter in the framework of light-front finite-temperature field theory. Presently we use the Nambu–Jona-Lasinio model of QCD and derive the gap equation at finite temperature and density. We study pionic and scalar diquark dynamics in quark matter and calculate the masses and the Mott dissociation as a function of the temperature T and the chemical potential μ. For the scalar diquark we determine the critical temperature of color superconductivity. 相似文献
16.
Zhi-Qing Zhang Zhen-Jun Xiao 《The European Physical Journal C - Particles and Fields》2009,59(1):49-66
We calculate the important next-to-leading-order (NLO) contributions to the B→KK
* decays from the vertex corrections, the quark loops, and the magnetic penguins in the perturbative QCD (pQCD) factorization
approach. The pQCD predictions for the CP-averaged branching ratios are
,
,
and Br(B
0→K
+
K
*−+K
−
K
*+)≈1.3×10−7, which agree well with both the experimental upper limits and the predictions based on the QCD factorization approach. Furthermore,
the CP violating asymmetries of the considered decay modes are also evaluated. The NLO pQCD predictions for
and
decays are
and
. 相似文献
17.
We calculate the one-photon loop radiative corrections to virtual pion Compton scattering
→
, that subprocess which determines in the one-photon exchange approximation the pion-nucleus bremsstrahlung reaction
Z →
Z
. Ultraviolet and infrared divergencies of the loop integrals are both treated by dimensional regularization. Analytical
expressions for the O() corrections to the virtual Compton scattering amplitudes, A(s, u, Q) and B(s, u, Q) , are derived with their full dependence on the (small) photon virtuality Q from 9 classes of contributing one-loop diagrams. Infrared finiteness of these virtual radiative corrections is achieved
(in the standard way) by including soft photon radiation below an energy cut-off . In the region of low
center-of-mass energies, where the pion-nucleus bremsstrahlung process is used to extract the pion electric and magnetic
polarizabilities, we find radiative corrections up to about -3% for = 5 MeV. Furthermore, we extend our calculation of the radiative corrections to virtual pion Compton scattering
→
by including the leading pion-structure effect in the form of the polarizability difference - . Our analytical results are particularly relevant for analyzing the data of the COMPASS experiment at CERN which aims at
measuring the pion electric and magnetic polarizabilities with high statistics using the Primakoff effect. 相似文献
18.
Omar Mustafa S. Habib Mazharimousavi 《International Journal of Theoretical Physics》2009,48(1):183-193
Non-Hermitian but
-symmetrized spherically-separable Dirac and Schr?dinger Hamiltonians are considered. It is observed that the descendant Hamiltonians
H
r
, H
θ
, and H
φ
play essential roles and offer some “user-feriendly” options as to which one (or ones) of them is (or are) non-Hermitian.
Considering a
-symmetrized H
φ
, we have shown that the conventional Dirac (relativistic) and Schr?dinger (non-relativistic) energy eigenvalues are recoverable.
We have also witnessed an unavoidable change in the azimuthal part of the general wavefunction. Moreover, setting a possible
interaction V(θ)≠0 in the descendant Hamiltonian H
θ
would manifest a change in the angular θ-dependent part of the general solution too. Whilst some
-symmetrized H
φ
Hamiltonians are considered, a recipe to keep the regular magnetic quantum number m, as defined in the regular traditional Hermitian settings, is suggested. Hamiltonians possess properties similar to the
-symmetric ones (here the non-Hermitian
-symmetric Hamiltonians) are nicknamed as pseudo-
-symmetric. 相似文献
19.
S. Abd El-Samad R. Bilger K. -Th. Brinkmann H. Clement M. Dietrich E. Doroshkevich S. Dshemuchadse K. Ehrhardt A. Erhardt W. Eyrich A. Filippi H. Freiesleben M. Fritsch R. Geyer A. Gillitzer J. Hauffe D. Hesselbarth R. Jaekel B. Jakob L. Karsch K. Kilian J. Kress E. Kuhlmann S. Marcello S. Marwinski R. Meier K. M?ller H. P. Morsch L. Naumann J. Ritman E. Roderburg P. Sch?nmeier M. Schulte-Wissermann W. Schroeder F. Stinzing G. Y. Sun J. W?chter G. J. Wagner M. Wagner U. Weidlich A. Wilms S. Wirth G. Zhang P. Zupranski 《The European Physical Journal A - Hadrons and Nuclei》2009,39(3):281-289
The single-pion production reactions pp
d
, pp
np
and pp
pp
were measured at a beam momentum of 0.95GeV/c ( T
p
400 MeV) using the short version of the COSY-TOF spectrometer. The central calorimeter provided particle identification,
energy determination and neutron detection in addition to time-of-flight and angle measurements from other detector parts.
Thus all pion production channels were recorded with 1-4 overconstraints. The main emphasis is put on the presentation and
discussion of the np
channel, since the results on the other channels have already been published previously. The total and differential cross-sections
obtained are compared to theoretical calculations. In contrast to the pp
channel we observe in the np
channel a strong influence of the excitation. In particular, the pion angular distribution exhibits a (3 cos2
+ 1) -dependence, typical for a pure s -channel excitation and identical to that observed in the d
channel. Since the latter is understood by a s -channel resonance in the 1
D
2
pn partial wave, we discuss an analogous scenario for the pn
channel. 相似文献
20.
D. Ebert R. N. Faustov V. O. Galkin 《The European Physical Journal C - Particles and Fields》2003,32(1):29-43
Semileptonic and non-leptonic decays of the B
c
meson to B
s
and B mesons, caused by the
quark transitions, are studied in the framework of the relativistic quark model. The heavy quark expansion in inverse powers of the active c and spectator
quark is used to simplify calculations while the final s and d quarks in the B
s
and B mesons are treated relativistically. The decay form factors are explicitly expressed through the overlap integrals of the meson wave functions in the whole accessible kinematical range. The obtained results are compared with the predictions of other approaches.Received: 14 August 2003, Revised: 3 September 2003, Published online: 7 November 2003 相似文献