99 research outputs found
A Tentative Description of Z_c,b States in Terms of Metastable Feshbach Resonances
We attempt a description of the recently discovered Z_{c,b} states in terms
of Feshbach resonances arising from the interaction between the `closed'
subspace of hadrocharmonium levels and the `open' one of open-charm/beauty
thresholds. We show how the neutrality of the X(3872) might be understood in
this scheme and provide a preliminary explanation of the pattern of the
measured total widths of X,Z_{c,b}.Comment: To appear in the proceedings of The 6th International Workshop on
Charm Physics (CHARM 2013
Doubly Charmed Tetraquarks in B_c and Xi_bc Decays
The phenomenology of the so-called X, Y and Z hadronic resonances is hard to
reconcile with standard charmonium or bottomonium interpretations. It has been
suggested that some of these new hadrons can possibly be described as tightly
bound tetraquark states and/or as loosely bound two-meson molecules. In the
present paper we focus on the hypothetical existence of flavored, doubly
charmed, tetraquarks. Such states might also carry double electric charge, and
in this case, if discovered, they could univocally be interpreted in terms of
compact tetraquarks. Flavored tetraquarks are also amenable to lattice studies
as their interpolating operators do not overlap with ordinary meson ones. We
show that doubly charmed tetraquarks could significantly be produced at LHC
from B_c or Xi_bc heavy baryons.Comment: 12 pages, 8 figures. Comments and references added. Version to appear
in Phys.Rev.
Flavored tetraquark spectroscopy
The recent confirmation of the charged charmonium like resonance Z(4430) by the LHCb experiment strongly suggests the existence of QCD multi quark bound states. Some preliminary results about hypothetical flavored tetraquark mesons are reported. Such states are particularly amenable to Lattice QCD studies as their interpolating operators do not overlap with those of ordinary hidden-charm mesons
Frustration driven structural distortion in VOMoO4
Nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR),
magnetization measurements and electronic structure calculations in VOMoO4 are
presented. It is found that VOMoO4 is a frustrated two-dimensional
antiferromagnet on a square lattice with competing exchange interactions along
the side J1 and the diagonal J2 of the square. From magnetization measurements
J1+J2 is estimated around 155 K, in satisfactory agreement with the values
derived from electronic structure calculations. Around 100 K a structural
distortion, possibly driven by the frustration, is evidenced. This distortion
induces significant modifications in the NMR and EPR spectra which can be
accounted for by valence fluctuations. The analysis of the spectra suggests
that the size of the domains where the lattice is distorted progressively grows
as the temperature approaches the transition to the magnetic ground state at
Tc=42 K
K^0-\bar{K}^0 mixing in the Standard Model from Nf=2+1+1 Twisted Mass Lattice QCD
We present preliminary results at {\beta} = 1.95 (a = 0.077 fm) on the first
unquenched N_f=2+1+1 lattice computation of the B_K parameter which controls
the neutral kaon oscillations in the Standard Model. Using N_f=2+1+1 maximally
twisted sea quarks and Osterwalder-Seiler valence quarks we achieve O(a)
improvement and a continuum-like renormalization pattern for the four-fermion
operator. Our results are extrapolated/interpolated to the physical
light/strange quark mass but not yet to the continuum limit. The computation of
the relevant renormalization constants is performed non perturbatively in the
RI'-MOM scheme using dedicated simulations with N_f=4 degenerate sea quark
flavours produced by the ETM collaboration.
We get B_K^{RGI} (a = 0.077) = 0.747(18), which when compared to our previous
unquenched N_f=2 determination and most of the existing results, suggests a
rather weak B_K^{RGI} dependence on the number of dynamical flavours. We are at
the moment analysing lattice data at two additional {\beta} values which will
allow us to perform an extrapolation to the continuum limit.Comment: 7 pages, 8 figures, Proceedings of Lattice 2011, XXIX International
Symposium on Lattice Field Theory, Squaw Valley, Lake Tahoe, Californi
Flavored tetraquark spectroscopy
The recent confirmation of the charged charmonium like resonance Z(4430) by
the LHCb experiment strongly suggests the existence of QCD multi quarks bound
states. Some preliminary results about hypothetical flavored tetraquark mesons
are reported. Such states are particularly amenable to Lattice QCD studies as
their interpolating operators do not overlap with those of ordinary
hidden-charm mesons.Comment: 7 pages, 7 figures, presented at the 32nd International Symposium on
Lattice Field Theory (Lattice 2014), June 23-28 2014, New York, US
Twisted mass fermions: neutral pion masses from disconnected contributions
Twisted mass fermions allow light quarks to be explored but with the
consequence that there are mass splittings, such as between the neutral and
charged pion. Using a direct calculation of the connected neutral pion
correlator and stochastic methods to evaluate the disconnected correlations, we
determine the neutral pion mass. We explore the dependence on lattice spacing
and quark mass in quenched QCD. For dynamical QCD, we determine the sign of the
splitting which is linked, via chiral PT, to the nature of the phase transition
at small quark mass.Comment: 6 pages, poster (hadron spectrum and quark masses) at Lattice
2005,Dublin, July 25-3
Neurite Orientation Dispersion and Density Imaging Color Maps to Characterize Brain Diffusion in Neurologic Disorders
Purpose: Neurite orientation dispersion and density imaging (NODDI) has recently been developed to overcome diffusion technique limitations in modeling biological systems. This manuscript reports a preliminary investigation into the use of a single color-coded map to represent NODDI-derived information.
Materials and methods: An optimized diffusion-weighted imaging protocol was acquired in several clinical neurological contexts including demyelinating disease, neoplastic process, stroke, and toxic/metabolic disease. The NODDI model was fitted to the diffusion datasets. NODDI is based on a three-compartment diffusion model and provides maps that quantify the contributions to the total diffusion signal in each voxel. The NODDI compartment maps were combined into a single 4-dimensional volume visualized as RGB image (red for anisotropic Gaussian diffusion, green for non-Gaussian anisotropic diffusion, and blue for isotropic Gaussian diffusion), in which the relative contributions of the different microstructural compartments can be easily appreciated.
Results: The NODDI color maps better describe the heterogeneity of neoplastic as well inflammatory lesions by identifying different tissue components within areas apparently homogeneous on conventional imaging. Moreover, NODDI color maps seem to be useful for identifying vasogenic edema differently from tumor-infiltrated edema. In multiple sclerosis, the NODDI color maps enable a visual assessment of the underlying microstructural changes, possibly highlighting an increased inflammatory component, within lesions and potentially in normal-appearing white matter.
Conclusion: The NODDI color maps could make this technique valuable in a clinical setting, providing comprehensive and accessible information in normal and pathological brain tissues in different neurological pathologies
Dynamic Critical Behavior of an Extended Reptation Dynamics for Self-Avoiding Walks
We consider lattice self-avoiding walks and discuss the dynamic critical
behavior of two dynamics that use local and bilocal moves and generalize the
usual reptation dynamics. We determine the integrated and exponential
autocorrelation times for several observables, perform a dynamic finite-size
scaling study of the autocorrelation functions, and compute the associated
dynamic critical exponents . For the variables that describe the size of the
walks, in the absence of interactions we find in two dimensions
and in three dimensions. At the -point in two dimensions
we have .Comment: laTeX2e, 32 pages, 11 eps figure
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