Search results for " phenomenology"
showing 10 items of 3693 documents
Meson loops in the $f_0(980)$ and $a_0(980)$ radiative decays into $\rho$, $\omega$
2008
We calculate the radiative decay widths of the $a_0(980)$ and $f_0(980)$ scalar mesons into $\rho\gamma$ and $\omega\gamma$ considering the dynamically generated nature of these scalar resonances within the realm of the Chiral Unitary Approach. The main ingredient in the evaluation of the radiative width of the scalar mesons are the loops coming from the decay into their constituent pseudoscalar-pseudoscalar components and the subsequent radiation of the photon. The dominant diagrams with only pseudoscalar mesons in the loops are found to be convergent while the divergence of those with a vector meson in the loop are written in terms of the two meson loop function easily regularizable. We p…
Meson-baryon threshold effects in the light-quark baryon spectrum
2008
We argue that selected $S$ wave meson-baryon channels may play a key role to match poor baryon mass predictions from quark models with data. The identification of these channels with effective inelastic channels in data analysis allows to derive a prescription which could improve the extraction and identification of baryon resonances.
Theoretical determination of the hadronic (g-2) of the muon
2016
An approach is discussed on the determination of the leading order hadronic contribution to the muon anomaly, $a_\mu^{HAD}$, based entirely on theory. This method makes no use of $e^+ e^-$ annihilation data, a likely source of the current discrepancy between theory and experiment beyond the $3\, \sigma$ level. What this method requires is essentially knowledge of the first derivative of the vector current correlator at zero-momentum. In the heavy-quark sector this is obtained from the well known heavy quark expansion in perturbative QCD, leading to values of $a_\mu^{HAD}$ in the charm- and bottom-quark region which were fully confirmed by later lattice QCD (LQCD) results. In the light-quark…
Semileptonic decays of light quarks beyond the Standard Model
2009
We describe non-standard contributions to semileptonic processes in a model independent way in terms of in SU(2)(L) x U(1)(Y) invariant effective lagrangian at the weak scale, front which we derive the low-energy effective lagrangian governing muon and beta decays. We find that the deviation from Cabibbo universality, Delta(CKM) equivalent to vertical bar V-ud vertical bar(2) + vertical bar V-us vertical bar(2) + vertical bar V-ub vertical bar(2) - 1, receives contributions from four effective operators. The phenomenological bound Delta(CKM) = (-1 +/- 6) x 10(-4) provides strong constraints on all four operators, corresponding to art effective scale Lambda > 11 TeV (90% CL). Depending on th…
The Heavy Quark Spin Symmetry Partners of the X(3872)
2012
We explore the consequences of heavy quark spin symmetry for the charmed meson-antimeson system in a contact-range (or pionless) effective field theory. As a trivial consequence, we theorize the existence of a heavy quark spin symmetry partner of the X(3872), with $J^{PC}=2^{++}$, which we call X(4012) in reference to its predicted mass. If we additionally assume that the X(3915) is a $0^{++}$ heavy spin symmetry partner of the X(3872), we end up predicting a total of six $D^{(*)}\bar{D}^{(*)}$ molecular states. We also discuss the error induced by higher order effects such as finite heavy quark mass corrections, pion exchanges and coupled channels, allowing us to estimate the expected theo…
Helicity-dependent generalized parton distributions and composite constituent quarks
2004
An approach, recently proposed to calculate the nucleon generalized parton distributions (GPDs) in a constituent quark model (CQM) scenario, in which the constituent quarks are taken as complex systems, is used to obtain helicity-dependent GPDs. They are obtained from the wave functions of the non relativistic CQM of Isgur and Karl, convoluted with the helicity-dependent GPDs of the constituent quarks themselves. The latter are modelled by using the polarized structure functions of the constituent quark, the double distribution representation of GPDs, and a phenomenological constituent quark form factor. The present approach permits to access a kinematical range corresponding to both the Do…
Chiral SU(3) Bethe Salpeter Model: Extension to SU(6) and SU(8) Spin-Flavor Symmetries
2008
Consistent SU(6) and SU(8) spin-flavor extensions of the SU(3) flavor Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian are constructed, which incorporate vector meson degrees of freedom. In the charmless sector, the on-shell approximation to the Bethe-Salpeter (BS) approach successfully reproduces previous SU(3) WT results for the lowest-lying s--wave negative parity baryon resonances. It also provides some information on the dynamics of heavier ones and of the lightest d-wave negative parity resonances, as e.g. the Lambda(1520). For charmed baryons the scheme is consistent with heavy quark symmetry, and our preliminary results in the strangeness-less charm C=+1 sector describe the mai…
Open-charm meson spectroscopy
2006
We present a theoretical framework that accounts for the new $D_J$ and $D_{sJ}$ mesons measured in the open-charm sector. These resonances are properly described if considered as a mixture of conventional $P-$wave quark-antiquark states and four-quark components. The narrowest states are basically $P-$wave quark-antiquark mesons, while the dominantly four-quark states are shifted above the corresponding two-meson threshold, being broad resonances. We study the electromagnetic decay widths as basic tools to scrutiny their nature. The proposed explanation incorporates in a natural way the most recently discovered mesons in charmonium spectroscopy.
A Heavy Quark Symmetry Approach to Baryons
2005
We evaluate different properties of baryons with a heavy c or b quark. The use of Heavy Quark Symmetry (HQS) provides with an important simplification of the non relativistic three body problem which can be solved by means of a simple variational approach. This scheme is able to reproduce previous results obtained with more involved Faddeev calculations. The resulting wave functions are parametrized in a simple manner, and can be used to calculate further observables.
Proton Spin in Chiral Quark Models
1997
The spin and flavor fractions of constituent quarks in the proton are obtained from their chiral fluctuations involving Goldstone bosons. SU(3) flavor symmetry breaking suggested by the mass difference between the strange and up, down quarks is included, and this improves the agreement with the data markedly.