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M. R. Pennington

Publications and source records attributed to M. R. Pennington.

At least 73 records · Page 4Linked to original sources
arXiv2002

Translating Quark Dynamics into Hadron Physics (and back again)

Why should we study mesons in 2002? Two approaches to relating quark and gluon dynamics to hadron physics, namely QCD sum rules and effective field theories, are briefly discussed. These are linked by progress in the study of strong QCD, both by lattice Monte Carlo methods and in the continuum. These provide the translation from quark dynamics to hadron physics and back again. Scope for more theoretical work and further experiments to elucidate the nature of the QCD vacuum and its precise relation to scalar mesons and their interactions is outlined.

hep-ph↗
arXiv2002

Dynamical Generation of Scalar Mesons

Starting with just one bare seed for each member of a scalar nonet, we investigate when it is possible to generate more than one hadronic state for each set of quantum numbers. In the framework of a simple model, we find that in the I=1 sector it is possible to generate two physical states with the right features to be identified with the a_0(980) and the a_0(1450). In the I=1/2 sector, we can generate a number of physical states with masses higher than 1 GeV, including one with the right features to be associated with the K_0^*(1470), but none which can be identified with the light kappa scalar meson. The I=0 sector is the most complicated and elusive: since all outcomes are very strongly model dependent, we cannot draw any robust conclusion. Nevertheless, we find that in that case too, depending on the coupling scheme adopted, the occurrence of numerous states can be achieved. This shows that dynamical generation of physical states is a possible solution to the problem of accounting for more scalar mesons than can fit in a single nonet, as experiments clearly deliver.

hep-ph↗
arXiv2001

QCD Finite Energy Sum Rules and the Isoscalar Scalar Mesons

We apply QCD Finite Energy Sum Rules to the scalar-isoscalar current to determine the lightest $u \bar{u} + d \bar{d}$ meson in this channel. We use `pinch-weights' to improve the reliability of the QCD predictions and reduce the sensitivity to the cut-off $s_0$. A decaying exponential is included in the weight function to allow us to focus on the contribution from low mass states to the phenomenological integral. On the theoretical side we include OPE contributions up to dimension six and a contribution due to instantons taken from the Instanton Liquid Model. Phenomenologically, we incorporate experimental data by using a coupling scheme for the scalar current which links the vacuum polarisation to the $ππ$ scattering amplitude via the scalar form factor. We find that the sum rules are well saturated for certain instanton parameters. We conclude that the $f_0(400-1200)$ definitely contains a large $u \bar{u} + d \bar{d}$ component, whereas the $f_0(980)$ most likely does not. We are able to estimate the average light quark mass and find $m_q(1 \GeV) = 5.2 \pm 0.6$ MeV.

hep-ph↗
arXiv2001

On Radiative $ϕ\to ηγ$, $ϕ\to η^\prime γ$ Decays

We use QCD sum-rules to study the decays $ϕ\to ηγ$ and $ϕ\to η^\prime γ$, obtaining ${\cal B}(ϕ\to ηγ)=(1.15 \pm 0.2) 10^{-2}$ and ${\cal B}(ϕ\to η^\prime γ)=(1.18 \pm 0.4) 10^{-4}$, in very good agreement with existing experimental data. We also discuss the issue of $η-η^\prime$ mixing, predicting the $η$ and $η^\prime$ decay constants in a mixing scheme in the quark-flavour basis.

hep-ph↗
arXiv2001

Radiative $ϕ$$-$meson decays and $η$-$η^\prime$ mixing: a QCD sum rule analysis

The radiative transitions $ϕ\to ηγ$ and $ϕ\to η^\prime γ$ are analysed using QCD sum-rules. The results we obtain for ${\cal B}(ϕ\to ηγ)=(1.15 \pm 0.2) 10^{-2}$ and ${\cal B}(ϕ\to η^\prime γ)=(1.18 \pm 0.4) 10^{-4}$ are in very good agreement with existing experimental data. The related issue of $η-η^\prime$ mixing is discussed and we give predictions for the $η$ and $η^\prime$ decay constants in the framework of a mixing scheme in the quark-flavour basis.

hep-ph↗
arXiv2001

Probing the structure of $f_0(980)$ through radiative $ϕ$ decays

We consider the radiative transition $ϕ\to f_0 γ$, which is a sensitive probe of the nature of the $f_0(980)$ particle. Using the QCD sum-rule technique, we estimate the branching ratio of such decay mode to be: ${\cal B}(ϕ\to f_0 γ)=(2.7 \pm 1.1) ~ 10^{-4}$, in fair agreement with present experimental data. As for the structure of the $f_0$, the result suggests a sizeable $s {\bar s}$ component; however, this result does not exclude the possibility of further components and allows a more complex structure than indicated by the naive quark model.

hep-ph↗
arXiv2000

There is no $κ(900)$

In the I=0 sector there are more scalar mesons than can fit in one $q{\bar q}$ nonet. Consequently, many have claimed that there is in fact more than one multiplet, perhaps both $q{\bar q}$ and $qq{\bar {qq}}$. Such proposals require the existence of at least two strange isodoublets (and their antiparticles). The current PDG Tables list just one state, the $K^*_0(1430)$, while fits to data with Breit-Wigner forms and variable backgrounds can accommodate a $κ(900)$ too. Whether a state exists in the spectrum of hadrons is not a matter of ability to fit data along the real energy axis, but is completely specified by the number of poles in the complex energy plane. Here we perform a model-independent analytic continuation of $πK$ scattering results between 825 MeV and 2 GeV to determine the number and position of resonance poles. We find that there {\bf is} a $K^*_0(1430)$, but {\bf no} $κ(900)$. The LASS data cannot rule out the possibility of a very low mass $κ$ well below 825 MeV.

hep-ph↗
arXiv2000

Does the weak coupling limit of the Burden-Tjiang deconstruction of the massless quenched QED3 vertex agree with perturbation theory?

We derive constraints on the non-perturbative 3-point fermion-boson transverse vertex in massless QED3 from its perturbative calculation to order $α$. We also check the transversality condition to two loops and evaluate the fermion propagator to the same order. We compare a conjecture of the non-perturbative vertex by Burden and Tjiang against our results and comment on its draw backs. Our calculation calls for the need to construct a non-perturbative form for the fermion-boson vertex which agrees with its perturbative limit to ${\cal O}(α)$.

hep-th↗
arXiv2000

Is the $σ(600)$ a Glueball? Two photon reactions can tell us

Minkowski and Ochs have recently argued that the small two photon coupling of a conjectured $σ(600)$ is so small that it is likely to be a glueball. We ask whether this can be so or whether it is simply gauge invariance that produces the observed low mass suppression?

hep-ph↗
arXiv2000

The Lightest Strange Scalar Resonance

I present the results of a recent calculation to determine the number of strange scalar resonances below 1.8 GeV based on the analytic properties of the experimental pi K scattering amplitude. Only one resonance was found in the data, and this is readily identifiable as the K_0^*(1430). We found no evidence to support the kappa(900).

hep-ph↗
arXiv2000

Low Energy Hadron Physics

Ask a group of particle theorists about low energy hadron physics and they will say that this is a subject that belongs to the age of the dinosaurs. However, it is GeV physics that controls the outcome of every hadronic interaction at almost every energy. Confinement of quarks and gluons (and any other super-constituents) means that it is the femto-universe that determines what experiments detect. What we have to learn at the start of the 21st century is discussed.

hep-ph↗
arXiv1999

Analytic Form of the One-loop Vertex and of the Two-loop Fermion Propagator in 3-Dimensional Massless QED

We evaluate the analytic expression for the one-loop fermion-boson vertex in massless QED3 in an arbitrary covariant gauge. The result is written in terms of elementary functions of its momenta. The vertex is decomposed into a longitudinal part, that is fully responsible for ensuring the Ward and Ward-Takahashi identities are satisfied, and a transverse part. Following Ball and Chiu and Kızılersü {\it et. al.}, the transverse part is written in its most general form as a function of 4 independent vectors. We calculate the coefficients of each of these vectors. We also check the transversality condition to two loops and evaluate the fermion propagator to the same order. We compare our results with a conjecture of the non-perturbative vertex by Tjiang and Burden.

hep-ph↗
arXiv1999

Riddle of the scalars: where is the sigma?

The riddle of the sigma is recast in a way that tries to differentiate fact from fiction as a basis for future/further discussion. By doing this, it is hoped that the role of the sigma as dominating the ubiquitous $ππ$ interactions below 1 GeV and its relation to the QCD vacuum can be clarified.

hep-ph↗
arXiv1998

Determination of Radiative Widths of Scalar Mesons from Experimental Results on $γγ\toππ$

The scalar mesons in the 1 GeV region constitute the Higgs sector of the strong interactions. They are responsible for the masses of all light flavour hadrons. However, the composition of these scalar states is far from clear, despite decades of experimental effort. The two photon couplings of the $f_{0}$'s are a guide to their structure. Two photon results from Mark II, Crystal Ball and CELLO prompt a new Amplitude Analysis of $γγ\toπ^+π^-$, $π^0π^0$ cross-sections. Despite their currently limited angular coverage and lack of polarized photons, we use a methodology that provides the nearest one can presently achieve to a model-independent partial wave separation. We find two distinct classes of solutions. Both have very similar two photon couplings for the $f_0(980)$ and $f_0(400-1200)$. Hopefully these definitive results will be a spur to dynamical calculations that will bring us a better understanding of these important states.

hep-ph↗
arXiv1998

Glueballs : the Naked Truth

The current status of the accepted glueball candidates is reviewed. The difference between bare and dressed hadrons is emphasised. What two photon processes, both production and decay, have taught us about these is discussed.

hep-ph↗
arXiv1998

Mass production requires precision engineering

This talk is in two parts both entitled mass production requires precision engineering. The first is about the dynamical generation of mass for matter particles in gauge theories. I will explain how the details of this depend on a precision knowledge of the interactions. The second is about tests of the mechanism of chiral symmetry breaking in QCD that the precision engineering of high luminosity colliders and particle detectors will shortly make possible. Since the latter topic has been described in Ref. 1, here I will just discuss the first: the production of mass from nothing.

hep-th↗