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G. Calderon

Publications and source records attributed to G. Calderon.

8 recordsLinked to original sources
arXiv2013

Axial-vector mesons from $τ\to APν_τ$ decays

Axial-vector mesons $a_1(1260)$, $f_1(1285)$, $h_1(1170)$, $K_1(1270)$, and $K_1(1400)$ can be produced in semileptonic $τ\to A P ν_τ$ decays, where $P$ stands for the pseudoscalar mesons $π$ or $K$. We calculate the branching ratios based in a meson dominance model. The exclusive channels $τ^-\to a_1(1260)^-π^0ν$, $τ^-\to a_1(1260)^0π^-ν$, and $τ^-\to h_1(1170)π^-ν$ turn out to be of order ${\cal O}(10^{-3})$, the channel $τ^-\to f_1(1285)π^-ν$ of order ${\cal O}(10^{-4})$, and channels $τ^-\to K_1(1270)^-π^0ν$, $τ^-\to K_1(1270)^0π^-ν$, $τ^-\to K_1(1400)^-π^0ν$, and $τ^-\to K_1(1400)^0π^-ν$ of order ${\cal O}(10^{-6})$. These results indicate that the branching ratios could be measured in experiments.

hep-ph↗
arXiv2013

Structural distortion in Ludwigites

Structural distortion in a three-leg-ladder is studied in connection with Ludwigites, in particular the Fe and Co homometallic ones. Static impurities in t_{2g}-orbitals as infinite repulsion potentials randomly located in the three-leg-ladder and a Su-Schrieffer-Heeger like tight-binding Hamiltonian are proposed and discussed. It is found that such potentials block itinerant electrons and diminish a structural staggered order parameter, related with structural distortion, as 3^{-M} being M the number of impurities. This diminution is in detriment of Peierls like distortion that occurs in these ladders as in the case of Fe-Ludwigite. On the other hand, this diminution could explain the lack of structural distortion as in the case of Co-Ludwigite.

cond-mat.str-el↗
arXiv2010

Branching ratios and CP asymmetries in charmless nonleptonic B decays to radially excited mesons

Nonleptonic two body B decays including radially excited $π(1300)$ or $ρ(1450)$ mesons in the final state are studied using the framework of generalized naive factorization approach. Branching ratios and CP asymmetries of $B\to Pπ(1300)$, $B\to Vπ(1300)$, $B\to Pρ(1450)$ and $B\to Vρ(1450)$ decays are calculated, where P and V stand for pseudoscalar and vector charmless mesons. Form factors for $B\to π(1300)$ and $B\to ρ(1450)$ transitions are estimated in the improved version of the Isgur-Scora-Grinstein-Wise quark model. In some processes, CP asymmetries of more than 10% and branching ratios of $10^{-5}$ order are found, which could be reached in experiments.

hep-ph↗
arXiv2008

Convolution formula and finite W boson width effects in the top quark width

In the standard model, the top quark decay width Γ_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 Γ_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=Γ(t-> bW) is recovered by taking the limit of massless fermions followed by the W boson narrow width approximation. Although both calculations of Γ_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.

hep-ph↗
arXiv2007

Nonleptonic two-body B-decays including axial-vector mesons in the final state

We present a systematic study of exclusive charmless nonleptonic two-body B decays including axial-vector mesons in the final state. We calculate branching ratios of B\to PA, VA and AA decays, where A, V and P denote an axial-vector, a vector and a pseudoscalar meson, respectively. We assume naive factorization hypothesis and use the improved version of the nonrelativistic ISGW quark model for form factors in B\to A transitions. We include contributions that arise from the effective ΔB=1 weak Hamiltonian H_{eff}. The respective factorized amplitude of these decays are explicitly showed and their penguin contributions are classified. We find that decays B^-to a_1^0π^-,\barB^0\to a_1^{\pm}π^{\mp}, B^-\to a_1^-\bar K^0, \bar B^0\to a_1^+K^-, \bar B^0\to f_1\bar K^0, B^-\to f_1K^-, B^-\to K_1^-(1400)\etap, B^-\to b_1^-\bar K^{0}, and \bar B^0\to b_1^+π^-(K^-) have branching ratios of the order of 10^{-5}. We also study the dependence of branching ratios for B \to K_1P(V,A) decays (K_1=K_1(1270),K_1(1400)) with respect to the mixing angle between K_A and K_B.

hep-ph↗
arXiv2007

Is there a paradox in CP asymmetries of tau to K_{L,S} pi nu decays?

Based on the description of unstable $K_{L,S}$ particles in quantum field theory (QFT), we compute the time-dependent probabilities for transitions between asymptotic states in $τ^{\pm} \to [π^+π^-]_Kπ^{\pm}ν$ decays, where the pair $[π^+π^-]_K$ is the product of (intermediate state) neutral kaon decays. Then we propose a definition of $τ$ decays into $K_L$ and $K_S$ 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 $K_{L,S}$ final states in $τ$ decays is motivated on experimental grounds, our predictions for the integrated CP rate asymmetries can be tested in a dedicated experiment.

hep-ph↗
arXiv2001

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.

hep-ph↗