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Adam P. Szczepaniak

Publications and source records attributed to Adam P. Szczepaniak.

89 records · Page 5Linked to original sources
arXiv2004

Chiral Symmetry and Hyperfine Quark-Antiquark Splittings

We briefly review theoretical calculations for the pseudoscalar-vector meson hyperfine splitting with no open flavor and also report a many body field theoretical effort to assess the impact of chiral symmetry in the choice of effective potentials for relativistic quark models. Our calculations predict the missing eta_b meson to have mass near 9400 $MeV$. The radial excitation $η_c(2S)$ is in agreement with the measurements of the BELLE and most recently BABAR collaborations.

hep-ph↗
arXiv2003

The low lying glueball spectrum

The complete low-lying positive charge conjugation glueball spectrum is obtained from QCD. The formalism relies on the construction of an efficient quasiparticle gluon basis for Hamiltonian QCD in Coulomb gauge. The resulting rapidly convergent Fock space expansion is exploited to derive quenched low-lying glueball masses with no free parameters which are in remarkable agreement with lattice gauge theory.

hep-ph↗
arXiv2003

Confinement and gluon propagator in Coulomb gauge QCD

We consider the effects of the Faddeev-Popov determinant in the Coulomb gauge on the confinement properties of the QCD vacuum. We show that the the determinant is needed to regularize the otherwise divergent functional integrals near the Gribov horizon but still enables large field configurations to generate IR enhanced running coupling. The physical gluon propagator is found to be strongly suppressed in the IR consistent with expectations from lattice gauge calculations.

hep-ph↗
arXiv2003

Study of the $ηπ$ and $η'π$ spectra and interpetation of possible exotic $J^{PC}=1^{-+}$ mesons

We discuss a coupled channel analysis of the $ηπ$ and $η'π$ systems produced in $π^-p$ interactions at 18 GeV/$c$. We show that known $Q\bar Q$ resonances, together with residual soft meson-meson rescattering, saturate the spectra including the exotic $J^{PC}=1^{-+}$ channel. A possibility of a narrow exotic resonance at a mass near 1.6 GeV/$c^2$ cannot, however, be ruled out.

hep-ph↗
arXiv2002

Spontaneous chiral symmetry breaking in the linked cluster expansion

We investigate dynamical chiral symmetry breaking in the Coulomb gauge Hamiltonian QCD. Within the framework of the linked cluster expansion we extend the BCS ansatz for the vacuum and include correlation beyond the quark-antiquark paring. In particular we study the effects of the three-body correlations involving quark-antiquark and transverse gluons. The high momentum behavior of the resulting gap equation is discussed and numerical computation of the chiral symmetry breaking is presented.

hep-ph↗
arXiv2002

Special relativity constraints on the effective constituent theory of hybrids

We consider a simplified constituent model for relativistic strong-interaction decays of hybrid mesons. The model is constructed using rules of renormalization group procedure for effective particles in light-front quantum field theory, which enables us to introduce low-energy phenomenological parameters. Boost covariance is kinematical and special relativity constraints are reduced to the requirements of rotational symmetry. For a hybrid meson decaying into two mesons through dissociation of a constituent gluon into a quark-anti-quark pair, the simplified constituent model leads to a rotationally symmetric decay amplitude if the hybrid meson state is made of a constituent gluon and a quark-anti-quark pair of size several times smaller than the distance between the gluon and the pair, as if the pair originated from one gluon in a gluonium state in the same effective theory.

hep-ph↗
arXiv2001

Coulomb Gauge QCD, Confinement, and the Constituent Representation

Quark confinement and the genesis of the constituent quark model are examined in nonperturbative QCD in Coulomb gauge. We employ a self-consistent method to construct a quasiparticle basis and to determine the quasiparticle interaction. The results agree remarkably well with lattice computations. They also illustrate the mechanism by which confinement and constituent quarks emerge, provide support for the Gribov-Zwanziger confinement scenario, clarify several perplexing issues in the constituent quark model, and permit the construction of an improved model of low energy QCD.

hep-ph↗
arXiv2001

Chiral Extrapolation, Renormalization, and the Viability of the Quark Model

The relationship of the quark model to the known chiral properties of QCD is a longstanding problem in the interpretation of low energy QCD. In particular, how can the pion be viewed as both a collective Goldstone boson quasiparticle and as a valence quark antiquark bound state where universal hyperfine interactions govern spin splittings in the same way as in the heavy quark systems. We address this issue in a simplified model which; however, reproduces all features of QCD relevant to this problem. A comparison of the many-body solution to our model and the constituent quark model demonstrates that the quark model is sufficiently flexible to describe meson hyperfine splitting provided proper renormalization conditions and correct degrees of freedom are employed consistently.

hep-ph↗
arXiv2001

Chiral Extrapolations and Exotic Meson Spectrum

We examine the chiral corrections to exotic meson masses calculated in lattice QCD. In particular, we ask whether the non-linear chiral behavior at small quark masses, which has been found in other hadronic systems, could lead to large corrections to the predictions of exotic meson masses based on linear extrapolations to the chiral limit. We find that our present understanding of exotic meson decay dynamics suggests that open channels may not make a significant contribution to such non-linearities whereas the virtual, closed channels may be important.

hep-ph↗
arXiv2001

Role of Photoproduction in Exotic Meson Searches

We discuss two production mechanisms of the $J^{PC}=1^{-+}$ exotic meson, hadroproduction, using pion beams and photoproduction. We show that the ratio of exotic to non-exotic, in particular the $a_2$, meson production cross sections is expected to be by a factor of 5 to 10 larger, in photoproduction then in hadroproduction. Furthermore we show that the low-t photoproduction of exotic meson is enhanced as compared to hadronic production. This findings support the simple quark picture in which exotic meson production is predicted to be enhanced when the beam is a virtual $Q\bar Q$ pair with a spin-1 (photon) rather then with a spin-0 (pion).

hep-ph↗
arXiv2000

QCD Glueball Regge Trajectories and the Pomeron

We report a glueball Regge trajectory emerging from diagonalizing a confining Coulomb gauge Hamiltonian for constituent gluons. Using a BCS vacuum ansatz and gap equation, the dressed gluons acquire a mass, of order 800 $MeV$, providing the quasiparticle degrees of freedom for a TDA glueball formulation. The TDA eigenstates for two constituent gluons have orbital, $L$, excitations with a characteristic energy of 400 $MeV$ revealing a clear Regge trajectory for $\vec{J} = \vec{L} + \vec{S}$, where $S$ is the total (sum) gluon spin. Significantly, the $S = 2$ glueball spectrum coincides with the Pomeron given by $α_P(t)=1.08+0.25 t $. Finally, we also ascertain that lattice data supports our result, yielding an average intercept of 1.1 in good agreement with the Pomeron.

hep-ph↗
arXiv2000

Nonperturbative Renormalization and the QCD Vacuum

We present a self consistent approach to Coulomb gauge Hamiltonian QCD which allows one to relate single gluon spectral properties to the long range behavior of the confining interaction. Nonperturbative renormalization is discussed. The numerical results are in good agreement with phenomenological and lattice forms of the static potential.

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arXiv1998

Sudakov suppression in the soft heavy to light meson transition form factor

We calculate hard gluon contribution to the decay vertex that determines the heavy-to-light meson transition form factor at large recoil. It is found that resulting Sudakov suppression significantly decreases the soft, wave function dependent contribution to the form factor. Phenomenological implications of these findings are discussed.

hep-ph↗
arXiv1997

Hybrid Decays

The heavy quark expansion of Quantum Chromodynamics and the strong coupling flux tube picture of nonperturbative glue are employed to develop the phenomenology of hybrid meson decays. The decay mechanism explicitly couples gluonic degrees of freedom to the pair produced quarks and hence does not obey the well known, but model-dependent, selection rule which states that hybrids do not decay to pairs of L=0 mesons. However, the nonperturbative nature of gluonic excitations in the flux tube picture leads to a new selection rule: light hybrids do not decay to pairs of identical mesons. New features of the model are highlighted and partial widths are presented for several low lying hybrid states.

hep-ph↗
arXiv1996

On the Dirac Structure of Confinement

The Dirac structure of confinement is shown to be of timelike-vector nature in the heavy quark limit of QCD. This stands in contradiction with the phenomenological success of the Dirac scalar confining potential. A resolution is achieved through the demonstration that an effective scalar interaction is dynamically generated by nonperturbative mixing between ordinary and hybrid $Q \bar Q$ states. The resolution depends crucially on the collective nature of the gluonic degrees of freedom. This implies that dynamical gluonic effects are vital when attempting to incorporate fine structure in models of the $Q \bar Q$ interaction.

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