44,627 research outputs found
Non-standard interactions in decays
Originally thought as clean processes to study the hadronization of the weak
currents, semileptonic tau lepton decays can be useful to set constraints on
non-standard (NS) weak interactions. In this talk we summarize our recent
studies on the effects of NS interactions in decays. We find that experimental data on
these decays provide strong constraints on NS scalar and tensor interactions,
respectively. Further improved measurements at Belle II and a better knowledge
of necessary tensor and scalar form factors will allow to set limits on these
NS interactions that are similar or better to contraints obtained from other
low-energy processes.Comment: 11 pages. Procs. 15th Int. Workshop on Tau Lepton Physics, Amsterdam,
24-28 september 201
Updating V_us from kaon semileptonic decays
We update the determination of |V_us| using semielectronic and semimuonic
decays of K mesons. A modest improvement of 15% with respect to its present
value is obtained for the error bar of this matrix element when we combine the
four available semileptonic decays. The combined effects of long-distance
radiative corrections and nonlinear terms in the vector form factors can
decrease the value of |V_us| by up to 1%. Refined measurements of the decay
widths and slope form factors in the semimuonic modes and a more accurate
calculation of vector form factors at zero momentum transfer can push the
determination of |V_us| at a few of percent level.Comment: 19 pages, 2 figure
Convolution formula and finite W boson width effects in the top quark width
In the standard model, the top quark decay width \Gamma_t is computed from
the exclusive t -> bW decay. We argue in favor of using the three body decays
t-> bf_i\bar{f}_j to compute \Gamma_t as a sum over these exclusive modes. As
dictated by the S-matrix theory, these three body decays of the top quark
involve only asymptotic states and incorporate the width of the W boson
resonance in a natural way. The convolution formula (CF) commonly used to
include the finite width effects is found to be valid, in the general case,
when the intermediate resonance couples to a conserved current (limit of
massless fermions in the case of W bosons). The relation Gamma_t=\Gamma(t-> bW)
is recovered by taking the limit of massless fermions followed by the W boson
narrow width approximation. Although both calculations of \Gamma_t are
different at the formal level, their results would differ only by tiny effects
induced by light fermion masses and higher order radiative corrections.Comment: 10 pages, published versio
Coverages on Inverse Semigroups
First we give a definition of a coverage on a inverse semigroup that is
weaker than the one gave by a Lawson and Lenz and that generalizes the
definition of a coverage on a semilattice given by Johnstone. Given such a
coverage, we prove that there exists a pseudogroup that is universal in the
sense that it transforms cover-to-join idempotent-pure maps into
idempotent-pure pseudogroup homomorphisms. Then, we show how to go from a
nucleus on a pseudogroup to a topological groupoid embedding of the
corresponding groupoids. Finally, we apply the results found to study Exel's
notions of tight filters and tight groupoids
Recovering the boundary path space of a topological graph using pointless topology
First, we generalize the definition of a locally compact topology given by
Paterson and Welch for a sequence of locally compact spaces to the case where
the underlying spaces are and sober. We then consider a certain
semilattice of basic open sets for this topology on the space of all paths on a
graph and impose relations motivated by the definitions of graph C*-algebra in
order to recover the boundary path space of a graph. This is done using
techniques of pointless topology. Finally, we generalize the results to the
case of topological graphs
Is there a paradox in CP asymmetries of tau to K_{L,S} pi nu decays?
Based on the description of unstable particles in quantum field
theory (QFT), we compute the time-dependent probabilities for transitions
between asymptotic states in
decays, where the pair is the product of (intermediate state)
neutral kaon decays. Then we propose a definition of decays into
and states, which reflects into the cancellation between their CP rate
asymmetries, thus solving in a natural way the paradox pointed out previously
in litterature. Since our definition of final states in decays
is motivated on experimental grounds, our predictions for the integrated CP
rate asymmetries can be tested in a dedicated experiment.Comment: 4 pages, 1 figur
Arithmetic and the standard electroweak theory
We propose the relations 1/e - e =3 and tan(2theta_W)=3/2, where e is the
positron charge and theta_W is the weak angle. Present experimental data
support these relations to a very high accuracy. We suggest that some duality
relates the weak isospin and hypercharge gauge groups of the standard
electroweak theory.Comment: Latex, 6 page
Relation between masses of particles and the Fermi constant in the electroweak Standard Model
An empirical formula relating the physical masses of elementary particles and
the Fermi constant is proposed. Although no mechanism or theoretical model
behind this formula is advocated, we seek for a possible physical
interpretation. If not a simple numerical coincidence, this formula may
motivate theorists to search for relations among the different sectors of the
Electroweak Standard model.Comment: 2 page
Unstable particles, gauge invariance and the Delta^{++} resonance parameters
The elastic and radiative pion(+)-proton scattering are studied in the
framework of an effective Lagrangian model for the Delta^{++} resonance and its
interactions. The finite width effects of this spin-3/2 resonance are
introduced in the scattering amplitudes through a complex mass scheme to
respect electromagnetic gauge invariance. The resonant pole (Delta^{++}) and
background contributions (rho^0, sigma, Delta and neutron states) are separated
according to the principles of the analytic S-matrix theory. The mass and width
parameters of the \Delta^{++} obtained from a fit to experimental data on the
total cross section are in agreement with the results of a model-independent
analysis based on the analytic S-matrix approach. The magnetic dipole moment
determined from the radiative pion-proton scattering is mu_Delta^{++}=(6.14 +/-
0.51) nuclear magnetons.Comment: 16 pages, 2 figures, Talk given at Zacatecas Forum in Physics, May
11-13, 2002, Zacatecas Mexic
On the physics of the hydrogen atom
In this work we investigate the -deformation of the dynamical
symmetry of the hydrogen atom using the theory of the quantum group .
We derive the energy spectrum in a physically consistent manner and find a
degeneracy breaking as well as a smaller Hilbert space. We point out that using
the deformed Casimir as was done before leads to inconsistencies in the
physical interpretation of the theory.Comment: 10 pages; major changes to section
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