Search results for "baryon"

Neutrino mass and baryon-number nonconservation in superstring models

1986

We propose new mechanisms for understanding neutrino masses in superstring models that contain ${\mathrm{E}}_{6}$-singlet zero-mass fields after compactification. We show that the low-energy gauge group of these models can be phenomenologically acceptable. We then comment on \ensuremath{\Delta}B=1 and \ensuremath{\Delta}B=2 baryon-number-violating processes in these models.

Improved comparison of bar P and P charge-to-mass ratios

1995

The measured ratio of charge-to-mass ratios for the antiproton and proton is 1.000 000 001 5 ± 0.000 000 001 1. This 1 part in 109 comparison (1 ppb) is possible because a single or p is now directly observed while trapped in an open access Penning trap. The comparison is the most accurate mass spectrometry of particles with opposite charge and is the most sensitive test of CPT invariance for a baryon system. It is 40 times more accurate than our earlier comparison with many trapped antiprotons and protons, and is more than 45 000 times more accurate than earlier comparisons made with other techniques.

Λb and Λc baryon decays at finite values of heavy quark masses

2000

Semileptonic decays of Lambda_b and Lambda_c baryons are studied within the Relativistic Three-Quark Model using finite heavy quark mass values. Employing the same parameters as have been used previously for the description of exclusive decays of heavy baryons in the heavy quark limit we calculate the six form factors of the process and the corresponding decay rates. Our calculation shows that the ``finite mass'' corrections are important in heavy-to-light transitions and are not negligible in heavy-to-heavy transitions.

A New Numerical Approach to Estimate the Sunyaev–Zel’dovich Effect

2013

Several years ago, we designed a particular ray tracing method. Combined with a Hydra parallel code (without baryons), it may compute some CMB anisotropies: weak lensing (WL) and Rees–Sciama (RS) effects. Only dark matter is fully necessary to estimate these effects. For very small angular scales, we made an exhaustive study leading to a lensing contribution slightly—but significantly—greater than previous ones. Afterwards, the same ray tracing procedure was included in a parallel Hydra code with baryons. The resulting code was then tested. This code is being currently applied to the study of the thermal and kinetic Sunyaev–Zel’dovich (SZ) contributions to the CMB anisotropies. We present h…

Including theΔ(1232)resonance in baryon chiral perturbation theory

2005

Baryon chiral perturbation theory with explicit $\ensuremath{\Delta}(1232)$ degrees of freedom is considered. The most general interactions of pions, nucleons, and \ensuremath{\Delta} consistent with all underlying symmetries as well as with the constraint structure of higher-spin fields are constructed. By use of the extended on-mass-shell renormalization scheme, a manifestly Lorentz-invariant effective-field theory with a systematic power counting is obtained. As applications, we discuss the mass of the nucleon, the pion-nucleon \ensuremath{\sigma} term, and the pole of the \ensuremath{\Delta} propagator.

$b\to c$ semileptonic decay of triply heavy baryons and $c\to s,d$ semileptonic decays of ground-state $cb$ baryons

2013

ERRATUM: “RELIABILITY OF THE DETECTION OF THE BARYON ACOUSTIC PEAK” (2009, ApJ, 696, L93)

2009

Due to an error in applying the passive evolution to transform Mg (z = 0) magnitudes to Mg (z = 0.3), the values of the magnitude limits for the samples DR7-LRG and DR7-LRG-VL quoted in Table 1 were not correct. The corrected Table 1 is appended below. Note that although the redshift limits of the sample DR7-LRG are the same as in Eisenstein et al. (2005), the magnitude limits are therefore slightly shifted (see Table 1). Once this fact is considered, figures and results are completely unaffected. We are very grateful to Eyal Kazin for pointing out the error.

Resonances in chiral unitary approaches

2008

The extension of chiral theories to the description of resonances, via the incorporation of unitarity in coupled channels, has provided us with a new theoretical perspective on the nature of some of the observed excited hadrons. In this contribution some of the early achievements in the field of baryonic resonances are reviewed, the recent evidence of the two-pole nature of the Lambda(1405) is discussed and results on charmed baryon resonances are presented.

Long-range chiral dynamics of Λ-hyperon in nuclear media

2008

We extend a chiral effective field theory approach to the Λ-nuclei interaction with the inclusion of the decuplet baryons. More precisely, we study the contributions due to the long-range two-pion exchange, with Σ and Σ* baryons in the internal baryonic lines considering Nh and Δh excitations. In particular, central and spin-orbit potentials are studied. For the former, regularization is needed and physical values of the cut-off give a large attraction, becoming necessary to include the repulsion of other terms not considered here. For the latter, in a model-independent framework, the inclusion of the decuplet supports the natural explanation of the smallness of the Λ-nuclear spin-orbit ter…

Fits of the baryon magnetic moments to the quark model and spectrum-generating SU(3)

1982

We show that for theoretical as well as phenomenological reasons the baryon magnetic moments that fulfill simple group transformation properties should be taken in intrinsic rather than nuclear magnetons. A fit of the recent experimental data to the reduced matrix elements of the usual octet electromagnetic current is still not good, and in order to obtain acceptable agreement, one has to add correction terms to the octet current. We have texted two kinds of corrections: U-spin-scalar terms, which are singles out by the model-independent algebraic properties of the hadron electromagnetic current, and octet U-spin vectors, which could come from quark-mass breaking in a nonrelativistic quark …