980 research outputs found
Meson-Baryon s-wave Resonances with Strangeness -3
Starting from a consistent SU(6) extension of the Weinberg-Tomozawa (WT)
meson-baryon chiral Lagrangian (Phys. Rev. D74 (2006) 034025), we study the
s-wave meson-baryon resonances in the strangeness S=-3 and negative parity
sector. Those resonances are generated by solving the Bethe-Salpeter equation
with the WT interaction used as kernel. The considered mesons are those of the
35-SU(6)-plet, which includes the pseudoscalar (PS) octet of pions and the
vector (V) nonet of the rho meson. For baryons we consider the 56-SU(6)-plet,
made of the 1/2+ octet of the nucleon and the 3/2+ decuplet of the Delta.
Quantum numbers I(J^P)=0(3/2^-) are suggested for the experimental resonances
Omega*(2250)- and Omega*(2380)-. Among other, resonances with I=1 are found,
with minimal quark content sss\bar{l}l', being s the strange quark and l, l'
any of the the light up or down quarks. A clear signal for such a pentaquark
would be a baryonic resonance with strangeness -3 and electric charge of -2 or
0, in proton charge units. We suggest looking for K- Xi- resonances with masses
around 2100 and 2240 MeV in the sector 1(1/2^-), and for pi Omega- and K- Xi*-
resonances with masses around 2260 MeV in the sector 1(3/2^-).Comment: 3 pages, 1 Postscript figure, 7 table
SU(6)SU(3)xSU(2) and SU(8)SU(4)xSU(2) Clebsch-Gordan coefficients
Tables of scalar factors are presented for 63x63 and 120x63 in
SU(8)SU(4)xSU(2), and for 35x35 and 56x35 in
SU(6)SU(3)xSU(2). Related tables for SU(4)SU(3)xU(1) and
SU(3)SU(2)xU(1) are also provided so that the Clebsch-Gordan
coefficients can be completely reconstructed. These are suitable to study
meson-meson and baryon-meson within a spin-flavor symmetric scheme.Comment: 30 pages, mostly table
Leptonic CP violating effective action for Dirac and Majorana neutrinos
In the Standard Model minimally extended to include massive neutrinos, we
compute the leading CP-violating zero temperature contributions to the one-loop
effective action induced by integration of the leptons. Such contributions
start at operators of dimension six and they are P even for Dirac neutrinos and
P even or odd for Majorana neutrinos. Dimension four operators are allowed in
the mixed Dirac-Majorana case. It is verified by explicit calculation that CP
can be violated in two generation settings for Majorana neutrinos. Using
different neutrino scenarios we give upper bounds for the couplings of the
CP-violating operators. As a rule, we find that lepton-induced couplings are
suppressed as compared to quark-induced couplings, whenever the latter are
allowed, nevertheless, through virtual lepton-number violating mechanisms,
Majorana neutrinos induce new CP-violating operators not present in the quark
or Dirac-neutrino cases.Comment: 47 pages, 4 figure
Anti-inflammatory activity of beta-sitosterol in a model of oxazolone-induced contact delayed type hypersensitivity.
Large Nc Weinberg-Tomozawa interaction and negative parity s--wave baryon resonances
It is shown that in the 70 and 700 SU(6) irreducible spaces, the SU(6)
extension of the Weinberg-Tomozawa (WT) s-wave meson-baryon interaction
incorporating vector mesons ({\it hep-ph/0505233}) scales as ,
instead of the well known behavior for its SU(3)
counterpart. However, the WT interaction behaves as order
within the 56 and 1134 meson-baryon spaces. Explicit expressions for the WT
couplings (eigenvalues) in the irreducible SU(2) spaces, for arbitrary
and , are given. This extended interaction is used as a kernel of
the Bethe-Salpeter equation, to study the large scaling of masses and
widths of the lowest--lying negative parity s-wave baryon resonances.
Analytical expressions are found in the limit, from which it
can be deduced that resonance widths and excitation energies behave
as order , in agreement with model independent arguments, and
moreover they fall in the 70-plet, as expected in constituent quark models for
an orbital excitation. For the 56 and 1134 spaces, excitation energies and
widths grow indicating that such resonances do not
survive in the large limit. The relation of this latter behavior
with the existence of exotic components in these resonances is discussed. The
interaction comes out repulsive in the 700.Comment: 21 pages, 3 figures, requires wick.sty and young.sty. Subsection
added. Conclusions revised. To appear in Physical Review
Non-localities and Fermi motion corrections in atoms
We evaluate the p-wave amplitudes from the chiral Lagrangians and from
there construct the p-wave part of the nucleus optical potential plus a
small s-wave part induced from the elementary p-wave amplitude and the nuclear
Fermi motion. Simultaneously, the momentum and energy dependence of the s-wave
optical potential, previously developed, are taken into account and shown to
generate a small p-wave correction to the optical potential. All the
corrections considered are small compared to the leading s-wave potential, and
lead to changes in the shifts and widths which are smaller than the
experimental errors.
A thorough study of the threshold region and low densities is conducted,
revealing mathematical problems for which a physical solution is given.Comment: revised version, 28 pages, Latex, 8 postscript figures. Submitted to
Nucl. Phys.
CCharPPI web server: computational characterization of proteinâprotein interactions from structure
The atomic structures of proteinâprotein interactions are central to understanding their role in biological systems, and a wide variety of biophysical functions and potentials have been developed for their characterization and the construction of predictive models. These tools are scattered across a multitude of stand-alone programs, and are often available only as model parameters requiring reimplementation. This acts as a significant barrier to their widespread adoption. CCharPPI integrates many of these tools into a single web server. It calculates up to 108 parameters, including models of electrostatics, desolvation and hydrogen bonding, as well as interface packing and complementarity scores, empirical potentials at various resolutions, docking potentials and composite scoring functions.The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Unions Seventh Framework Programme (FP7/2007-
2013) under REA grant agreement PIEF-GA-2012-327899 and grant BIO2013-48213-R from Spanish Ministry of Economy and
Competitiveness.Peer ReviewedPostprint (published version
D mesic nuclei
The energies and widths of several D^0 meson bound states for different
nuclei are obtained using a D-meson selfenergy in the nuclear medium, which is
evaluated in a selfconsistent manner using techniques of unitarized
coupled-channel theory. The kernel of the meson-baryon interaction is based on
a model that treats heavy pseudoscalar and heavy vector mesons on equal
footing, as required by heavy quark symmetry. We find D^0 bound states in all
studied nuclei, from 12C up to 208Pb. The inclusion of vector mesons is the
keystone for obtaining an attractive D-nucleus interaction that leads to the
existence of D^0-nucleus bound states, as compared to previous studies based on
SU(4) flavor symmetry. In some cases, the half widths are smaller than the
separation of the levels, what makes possible their experimental observation by
means of a nuclear reaction. This can be of particular interest for the future
PANDA@FAIR physics program. We also find a D^+ bound state in 12C, but it is
too broad and will have a significant overlap with the energies of the
continuum.Comment: 13 pages, 6 figures, 2 table
Biological and Pharmacological aspects of the NK1-Receptor.
The neurokinin 1 receptor (NK-1R) is the main receptor for the tachykinin family of peptides. Substance P (SP) is the major mammalian ligand and the one with the highest affinity. SP is associated with multiple processes: hematopoiesis, wound healing, microvasculature permeability, neurogenic inflammation, leukocyte trafficking, and cell survival. It is also considered a mitogen, and it has been associated with tumorigenesis and metastasis. Tachykinins and their receptors are widely expressed in various human systems such as the nervous, cardiovascular, genitourinary, and immune system. Particularly, NK-1R is found in the nervous system and in peripheral tissues and are involved in cellular responses such as pain transmission, endocrine and paracrine secretion, vasodilation, and modulation of cell proliferation. It also acts as a neuromodulator contributing to brain homeostasis and to sensory neuronal transmission associated with depression, stress, anxiety, and emesis. NK-1R and SP are present in brain regions involved in the vomiting reflex (the nucleus tractus solitarius and the area postrema). This anatomical localization has led to the successful clinical development of antagonists against NK-1R in the treatment of chemotherapy-induced nausea and vomiting (CINV). The first of these antagonists, aprepitant (oral administration) and fosaprepitant (intravenous administration), are prescribed for high and moderate emesis
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