Search results for "UNITARITY"
showing 10 items of 245 documents
On the corner elements of the CKM and PMNS matrices
2013
Recent experiments show that the top-right corner element (U-e3) of the PMNS matrix is small but nonzero, and suggest further via unitarity that it is smaller than the bottom-left corner element (U-tau 1). Here, it is shown that if to the assumption of a universal rank-one mass matrix, long favoured by phenomenologists, one adds that this matrix rotates with scale, then it follows that A) by inputting the mass ratios m(c)/m(t), m(s)/m(b), m(mu)/m(tau), and m(2)/m(3), i) the corner elements are small but nonzero, ii) V-ub < V-td, U-e3 < U-tau 1, iii) estimates result for the ratios V-ub/V-td and U-e3/U-tau 1, and B) by inputting further the experimental values of V-us, V-tb and U-e2, U-mu 3,…
Eta photoproduction from nuclei
2008
Low-energy eta photoproduction from complex nuclei is investigated in a distorted wave impulse approximation (DWIA) framework carried out in momentum spaces. The elementary operator is fixed by the hadronic reactions πN→πN, πN→ππN and π−p→ηn as well as the process γN→πN to constrain the electromagnetic vertex. The resonances S11(1535), P11(1440) and D13(I520) are used to generate s-, p- and d-wave interactions. This coupled channels approach fulfils unitarity and allows the prediction of γp→ηp cross sections. The η final state interaction has been included via a simple optical potential using the ηN t-matrix as an input. We find that coherent eta production is dominated by the D13(1520) iso…
Charm-beauty meson bound states from B(B*)D(D*) and B(B*)D¯(D¯*) interaction
2017
We evaluate the $s$-wave interaction of pseudoscalar and vector mesons with both charm and beauty to investigate the possible existence of molecular $BD$, ${B}^{*}D$, $B{D}^{*}$, ${B}^{*}{D}^{*}$, $B\overline{D}$, ${B}^{*}\overline{D}$, $B{\overline{D}}^{*}$, or ${B}^{*}{\overline{D}}^{*}$ meson states. The scattering amplitude is obtained implementing unitarity starting from a tree level potential accounting for the dominant vector meson exchange. The diagrams are evaluated using suitable extensions to the heavy flavor sector of the hidden gauge symmetry Lagrangians involving vector and pseudoscalar mesons, respecting heavy quark spin symmetry. We obtain bound states at energies above 7 Ge…
Theoretical study of the Ξ(1620) and Ξ(1690) resonances in Ξc→π+MB decays
2017
Nonleptonic weak decays of ${\mathrm{\ensuremath{\Xi}}}_{c}$ into ${\ensuremath{\pi}}^{+}$ and a meson $(M)$-baryon $(B)$ final state, $MB$, are analyzed from the viewpoint of probing $S=\ensuremath{-}2$ baryon resonances, i.e., $\mathrm{\ensuremath{\Xi}}(1620)$ and $\mathrm{\ensuremath{\Xi}}(1690)$, of which spin-parity and other properties are not well known. We argue that the weak decay of ${\mathrm{\ensuremath{\Xi}}}_{c}$ is dominated by a single quark-line diagram, preferred by the Cabibbo-Kobayashi-Maskawa coefficient, color recombination factor, the diquark correlation, and the kinematical condition. The decay process has an advantage of being free from meson resonances in the ${\ens…
Unified description of hadronic and electromagnetic reactions of the two-nucleon system
2010
Abstract Studies of the two-nucleon system are essential for a profound understanding of nuclear structure and for the exploration of the limits of the effective description of atomic nuclei in terms of nucleons, mesons and isobars. In the present work, a unified description of hadronic and electromagnetic reactions on the two-nucleon system is developed in the framework of a coupled-channel N N / N Δ -approach which is based on one general Hamiltonian and which treats the pion exchange in the hadronic baryon–baryon interaction as well as in the meson exchange currents in the exact retarded manner. Unitarity and gauge invariance are at least approximately fulfilled. Several hadronic and ele…
Reduced hadronic uncertainty in the determination of $V_{ud}$
2018
We analyze the universal radiative correction $\Delta_R^V$ to neutron and superallowed nuclear $\beta$ decay by expressing the hadronic $\gamma W$-box contribution in terms of a dispersion relation, which we identify as an integral over the first Nachtmann moment of the $\gamma W$ interference structure function $F_3^{(0)}$. By connecting the needed input to existing data on neutrino and antineutrino scattering, we obtain an updated value of $\Delta_R^V = 0.02467(22)$, wherein the hadronic uncertainty is reduced. Assuming other Standard Model theoretical calculations and experimental measurements remain unchanged, we obtain an updated value of $|V_{ud}| = 0.97366(15)$, raising tension with …
Dispersive Evaluation of the Inner Radiative Correction in Neutron and Nuclear $\beta$-decay
2019
We propose a novel dispersive treatment of the so-called inner radiative correction to the neutron and nuclear $\beta$-decay. We show that it requires knowledge of the parity-violating structure function $F_3^{(0)}$ that arises from the interference of the axial vector charged current and the isoscalar part of the electromagnetic current. By isospin symmetry, we relate this structure function to the charged current inelastic scattering of neutrinos and antineutrinos. Applying this new data-driven analysis we obtain a new, more precise evaluation for the universal radiative correction $\Delta_{R}^{V,\,new}=0.02467(22)$ that supersedes the previous estimate by Marciano and Sirlin, $\Delta_R^V…
Single-energy partial wave analysis for pion photoproduction with fixed-t analyticity
2021
Experimental data for pion photoproduction including differential cross sections and various polarization observables from four reaction channels, $\gamma p \to \pi^0 p$, $\gamma p \to \pi^+n$, $\gamma n \to \pi^- p$ and $\gamma n \to \pi^0 n$ from threshold up to $W=2.2$ GeV have been used in order to perform a single-energy partial wave analysis with minimal model dependence by imposing constraints from unitarity and fixed-$t$ analyticity in an iterative procedure. Reaction models were only used as starting point in the very first iteration. We demonstrate that with this procedure partial wave amplitudes can be obtained which show only a minimal dependence on the initial model assumptions…
Watson’s theorem and theNΔ(1232)axial transition
2016
We present a new determination of the $N\mathrm{\ensuremath{\Delta}}$ axial form factors from neutrino induced pion production data. For this purpose, the model of Hernandez et al. [Phys. Rev. D 76, 033005 (2007)] is improved by partially restoring unitarity. This is accomplished by imposing Watson's theorem on the dominant vector and axial multipoles. As a consequence, a larger ${C}_{5}^{A}(0)$, in good agreement with the prediction from the off-diagonal Goldberger-Treiman relation, is now obtained.
A pedagogical approach to the Magnus expansion
2010
Time-dependent perturbation theory as a tool to compute approximate solutions of the Schrodinger equation does not preserve unitarity. Here we present, in a simple way, how the Magnus expansion (also known as exponential perturbation theory) provides such unitary approximate solutions. The purpose is to illustrate the importance and consequences of such a property. We suggest that the Magnus expansion may be introduced to students in advanced courses of quantum mechanics.