Search results for "Approx"
showing 10 items of 922 documents
Renormalized Proton-Neutron Quasiparticle Random-Phase Approximation and Its Application to Double Beta Decay
1995
A self-consistent method of treating excitations of the proton-neutron quasiparticle random-phase approximation is presented. The non-self-consistent methods violate the Pauli exclusion principle and lead to an eventual collapse of the ground state. This behavior renders a reliable calculation of the nuclear matrix elements, relevant for the prediction of double-beta-decay half-lives, difficult. The present formalism promotes the Pauli exclusion principle and avoids the collapse of the double-beta-decay matrix elements. We have applied this formalism to the double beta decay of ${}^{100}$Mo.
Pseudoscalar decays into lepton pairs from rational approximants
2016
The pseudoscalar decays into lepton pairs P! ‘‘ are analyzed with the machinery of Canterbury approximants, an extension of Pade approximants to bivariate functions. This framework provides an ideal model-independent approach to implement all our knowledge of the pseudoscalar transition form factors driving these decays, can be used for data analysis, and allows to include experimental data and theoretical constraints in an easy way, and determine a systematic error. We find that previous theoretical estimates for these branching ratios have underestimated their theoretical uncertainties. From our updated results, the existing experimental discrepancies for p 0 ! e + e and h! m + m channels…
The Kadanoff–Baym approach to double excitations in finite systems
2011
We benchmark many-body perturbation theory by studying neutral, as well as non-neutral, excitations of finite lattice systems. The neutral excitation spectra are obtained by time-propagating the Kadanoff-Baym equations in the Hartree-Fock and second Born approximations. Our method is equivalent to solving the Bethe-Salpeter equation with a high-level kernel while respecting self-consistently, which guarantees the fulfillment of a frequency sum rule. As a result, we find that a time-local method, such as Hartree-Fock, can give incomplete spectra, while already the second Born, which is the simplest time-nonlocal approximation, reproduces well most of the additional excitations, which are cha…
Waveguide-QED-based measurement of a reservoir spectral density
2015
The spectral density (SD) function has a central role in the study of open quantum systems (OQSs). We discover a method allowing for a "static" measurement of the SD - i.e., it requires neither the OQS to be initially excited nor its time evolution tracked in time - which is not limited to the weak-coupling regime. This is achieved through one-dimensional photon scattering for a zero-temperature reservoir coupled to the OQS via the rotating wave approximation. We find that the SD profile is a universal simple function of the photon's reflectance and transmittance. As such, it can be straightforwardly inferred from photon's reflection and transmission spectra.
Initial correlations effects on decoherence at zero temperature
2004
We consider a free charged particle interacting with an electromagnetic bath at zero temperature. The dipole approximation is used to treat the bath wavelengths larger than the width of the particle wave packet. The effect of these wavelengths is described then by a linear Hamiltonian whose form is analogous to phenomenological Hamiltonians previously adopted to describe the free particle-bath interaction. We study how the time dependence of decoherence evolution is related with initial particle-bath correlations. We show that decoherence is related to the time dependent dressing of the particle. Moreover because decoherence induced by the T=0 bath is very rapid, we make some considerations…
Relaxation due to random collisions with a many-qudit environment
2008
We analyze the dynamics of a system qudit of dimension mu sequentially interacting with the nu-dimensional qudits of a chain playing the ore of an environment. Each pairwise collision has been modeled as a random unitary transformation. The relaxation to equilibrium of the purity of the system qudit, averaged over random collisions, is analytically computed by means of a Markov chain approach. In particular, we show that the steady state is the one corresponding to the steady state for random collisions with a single environment qudit of effective dimension nu_e=nu*mu. Finally, we numerically investigate aspects of the entanglement dynamics for qubits (mu=nu=2) and show that random unitary …
QCD corrections to inclusive ΔS = 1, 2 transitions at the next-to-leading order
1994
24 páginas, 3 figuras, 2 tablas.-- arXiv:hep-ph/9402363v1
Measurement of Proton Electromagnetic Form Factors in e+e−→pp¯ in the Energy Region 2.00–3.08 GeV
2020
The process of e+e−→pp¯ is studied at 22 center-of-mass energy points (s) from 2.00 to 3.08 GeV, exploiting 688.5 pb−1 of data collected with the BESIII detector operating at the BEPCII collider. The Born cross section (σpp¯) of e+e−→pp¯ is measured with the energy-scan technique and it is found to be consistent with previously published data, but with much improved accuracy. In addition, the electromagnetic form-factor ratio (|GE/GM|) and the value of the effective (|Geff|), electric (|GE|), and magnetic (|GM|) form factors are measured by studying the helicity angle of the proton at 16 center-of-mass energy points. |GE/GM| and |GM| are determined with high accuracy, providing uncertaintie…
Including Tetraquark Operators in the Low-Lying Scalar Meson Sectors in Lattice QCD
2019
Lattice QCD allows us to probe the low-lying hadron spectrum in finite-volume using a basis of single- and multi-hadron interpolating operators. Here we examine the effect of including tetraquark operators on the spectrum in the scalar meson sectors containing the $K_0^*(700)$ ($\kappa$) and the $a_0(980)$ in $N_f = 2 + 1$ QCD, with $m_\pi \approx 230$ MeV. Preliminary results of additional finite-volume states found using tetraquark operators are shown, and possible implications of these states are discussed.
Dynamics of H2 molecule driven by an ultra-short laser field
2004
We describe, using a semiclassical approach, the molecular dynamics of a one-dimensional H2 molecule interacting with a laser, beyond the Born–Oppenheimer approximation. We observe and discuss different molecular behaviors, such as ionization and dissociation.