arXiv subjects

M. Ladisa

Publications and source records attributed to M. Ladisa.

16 recordsLinked to original sources

arXiv2008

Ab initio GW many-body effects in graphene

We present an {\it ab initio} many-body GW calculation of the self-energy, the quasiparticle band plot and the spectral functions in free-standing undoped graphene. With respect to other approaches, we numerically take into account the full ionic and electronic structure of real graphene and we introduce electron-electron interaction and correlation effects from first principles. Both non-hermitian and also dynamical components of the self-energy are fully taken into account. With respect to DFT-LDA, the Fermi velocity is substantially renormalized and raised by a 17%, in better agreement with magnetotransport experiments. Furthermore, close to the Dirac point the linear dispersion is modified by the presence of a kink, as observed in ARPES experiments. Our calculations show that the kink is due to low-energy $π\to π^*$ single-particle excitations and to the $π$ plasmon. Finally, the GW self-energy does not open the band gap.

cond-mat.mtrl-sci↗

arXiv2005

Model independent pre-processing of X-ray powder diffraction profiles

Precise knowledge of X-ray diffraction profile shape is crucial in the investigation of the properties of matter in crystals powder. Line-broadening analysis is a pre-processing step in most of the full powder pattern fitting softwares. Final result of line-broadening analysis strongly depends on preliminary three steps: Noise filtering, removal of background signal and peak fitting. In this work a new model independent procedure for two of the aforementioned steps (background suppression and peak fitting) is presented. The former is dealt with by using morphological mathematics, while the latter relies on the Hankel Lanczos Singular Value Decomposition technique. Real X-ray powder diffraction (XRPD) intensity profiles of Ceria samples are used to test the performance of the proposed procedure. Results show the robustness of this approach and its capability of efficiently improving the disentangling of instrumental broadening. These features make the proposed approach an interesting and user-friendly tool for the pre-processing of XRPD data.

math.SP↗

arXiv2005

Application of the HLSVD technique to the filtering of X-ray diffraction data

A filter based on the Hankel Lanczos Singular Value Decomposition (HLSVD) technique is presented and applied for the first time to X-ray diffraction (XRD) data. Synthetic and real powder XRD intensity profiles of nanocrystals are used to study the filter performances with different noise levels. Results show the robustness of the HLSVD filter and its capability to extract easily and efficiently the useful crystallographic information. These characteristics make the filter an interesting and user-friendly tool for processing XRD data.

math.SP↗

arXiv2005

Disentangling instrumental broadening

A new procedure aiming at disentangling the instrumental profile broadening and the relevant X-ray powder diffraction (XRPD) profile shape is presented. The technique consists of three steps: denoising by means of wavelet transforms, background suppression by morphological functions and deblurring by a Lucy--Richardson damped deconvolution algorithm. Real XRPD intensity profiles of ceria samples are used to test the performances. Results show the robustness of the method and its capability of efficiently disentangling the instrumental broadening affecting the measurement of the intrinsic physical line profile. These features make the whole procedure an interesting and user-friendly tool for the pre-processing of XRPD data.

cond-mat.mtrl-sci↗

arXiv2005

Nanoparticle size distribution estimation by full-pattern powder diffraction analysis

The increasing scientific and technological interest in nanoparticles has raised the need for fast, efficient and precise characterization techniques. Powder diffraction is a very efficient experimental method, as it is straightforward and non-destructive. However, its use for extracting information regarding very small particles brings some common crystallographic approximations to and beyond their limits of validity. Powder pattern diffraction calculation methods are critically discussed, with special focus on spherical particles with log-normal distribution, with the target of determining size distribution parameters. A 20-nm CeO$_{2}$ sample is analyzed as example.

cond-mat.mtrl-sci↗

arXiv2003

Charming penguins in B => K* pi, K (rho,omega,phi) decays

We evaluate the decays B => K* pi, K (rho,omega,phi) adding the long distance charming penguin contributions to the short distance: Tree+Penguin amplitudes. We estimate the imaginary part of the charming penguin by an effective field theory inspired by the Heavy Quark Effective Theory and parameterize its real part. The final results for branching ratios depend on only two real parameters and show a significant role of the charming penguins. The overall agreement with the available experimental data is satisfactory.

hep-ph↗

arXiv2002

Charming penguin contributions to charmless B decays into two pseudoscalar mesons

We present estimates of the charming penguin contribution to B => K pi, pi pi,K eta, K eta' decays due to intermediate charmed meson states. We find that this contribution is indeed significant for B => K pi decays, and its inclusion, together with the tree and penguin terms, produces large branching ratios in agreement with data, though the analysis is affected by large theoretical uncertainties. On the other hand, for B => pi pi, K eta, K eta' decays, the effect of the charming penguin contribution is more modest. We also compute CP asymmetries for B => K pi, pi pi decays and we obtain rather large results.

hep-ph↗

arXiv2001

Semileptonic and nonleptonic B decays to three charm quarks: B->J/psi (eta_c) D l nu and J/psi (eta_c) D pi

We evaluate the form factors describing the semileptonic decays $\bar{B^0}\to J/ψ(η_c) D^+ \ell^- \bar ν_\ell$, within the framework of a QCD relativistic potential model. This decay is complementary to $\bar{B^0}\to J/ψ(η_c) D^+ π^-$ in a phase space region where a pion factors out.We estimate the branching ratio for these semileptonic and nonleptonic channels, finding $\mathcal{BR}(\bar{B^0} \to J/ψ(η_c) D^+ \ell ν_\ell) \simeq 10^{-13}$, $\mathcal{BR}(\bar{B^0} \to J/ψD^+ π^-) = 3.1 \times 10^{-8}$ and $\mathcal{BR}(\bar{B^0} \to η_c D^+ π^-) = 3.5 \times 10^{-8}$.

hep-ph↗

arXiv2001

Charming penguin contributions to B => K π

We present calculations of the charming-penguin long-distance contributions to B => K πdecays due to intermediate charmed meson states. Our calculation is based on the Chiral Effective Lagrangean for light and heavy mesons, corrected for the hard pion and kaon momenta. We find that the charming-penguin contributions increase significantly the B => K πdecay rates in comparison with the short-distance contributions, giving results in better agreement with experimental data.

hep-ph↗

arXiv2000

B and B_s decays into three pseudoscalar mesons and the determination of the angle gamma of the unitarity triangle

We reconsider two classical proposals for the determination of the angle gamma of the unitarity triangle: B^\pm => chi_{c0} π^\pm => π^+π^-π^\pm and B_s => rho^0 K_S => π^+ π^- K_S. We point out the relevance, in both cases, of non resonant amplitudes, where the π^+ π^- pair is produced by weak decay of a B^* (J^P=1^-) or B_0 (J^P=0^+) off-shell meson. In particular, for the B decay channel, the inclusion of the B_0 pole completes some previous analyses and confirms their conclusions, provided a suitable cut in the Dalitz plot is performed; for the B_s decay the inclusion of the B^*, B_0 amplitudes enhances the role of the tree diagrams as compared to penguin amplitudes, which makes the theoretical uncertainty related to the B_s => rho^0 K_S decay process less significant. While the first method is affected by theoretical uncertainties, the second one is cleaner, but its usefulness will depend on the available number of events to perform the analysis.

hep-ph↗

arXiv2000

Measuring B -> rho pi decays and the unitarity angle alpha

The decay mode B -> rho pi is currently studied as a channel allowing, in principle, to measure without ambiguities the angle alpha of the unitarity triangle. It is also investigated by the CLEO Collaboration where a branching ratio larger than expected for the decay mode B+/- -> rho0 pi+/- has been found. We investigate the role that the B* and B(0+) resonances play in these analyses.

hep-ph↗

arXiv1999

B => ππ\ell νdecays in a QCD relativistic potential model

In the framework of a QCD relativistic potential model we evaluate the form factors describing the exclusive decay B => ππ\ell ν. The calculation is performed in a phase space region far away from the resonances and therefore is complementary to other decay mechanisms where the pions are produced by intermediate particles, e.g. in the chiral approach. We give an estimate of the contribution of the non resonant channel of the order of BR(B- => π+ π- \ell ν) \approx 2.2 x 10^(-4).

hep-ph↗

arXiv1999

Cottingham formula and the pion electromagnetic mass difference at finite temperature

We generalize the Cottingham formula at finite (T\neq 0) temperature by using the imaginary time formalism. The Cottingham formula gives the theoretical framework to compute the electromagnetic mass differences of the hadrons using a dispersion relation approach. It can be also used in other contexts, such as non leptonic weak decays, and its generalization to finite temperature might be useful in evaluating thermal effects in these processes. As an application we compute the π^+-π^0 mass difference at T\neq 0; at small T we reproduce the behaviour found by other authors: δm^2(T)= δm^2(0)+\mathcal{O}(αT^2), while for moderate T, near the deconfinement temperature, we observe deviations from this behaviour.

hep-ph↗

arXiv1999

Semileptonic and rare B meson decays into a light pseudoscalar meson

In the framework of a QCD relativistic potential model we evaluate the form factors describing the exclusive decays B => πl nu and B => K l+ l-. The present calculation extends a previous analysis of B meson decays into light vector mesons. We find results in agreement with the data, when available, and with the theoretical constraints imposed by the Callan-Treiman relation and the infinite heavy quark mass limit.

hep-ph↗

arXiv1998

Semileptonic and Rare $B$-meson transitions in a QCD relativistic potential model

Using a QCD relativistic potential model, previously applied to the calculation of the heavy meson leptonic constants, we evaluate the form factors governing the exclusive decays $B\toρ\ellν$, $B\to K^*γ$ and $B\to K^*\ell^+\ell^-$. In our approach the heavy meson is described as a $Q\bar q$ bound state, whose wave function is solution of the relativistic Salpeter equation, with an instantaneous potential displaying Coulombic behaviour at small distances and linear behaviour at large distances. The light vector meson is described by using a vector current interpolating field, according to the Vector Meson Dominance assumption. A Pauli-Villars regularized propagator is assumed for the quarks not constituting the heavy meson. Our procedure allows to avoid the description of the light meson in terms of wave function and constituent quarks, and consequently the problem of boosting the light meson wave function. Assuming as an input the experimental results on $B\to K^*γ$, we evaluate all the form factors describing the $B\to ρ, K^*$ semileptonic and rare transitions. The overall comparison with the data, whenever available, is satisfactory.

hep-ph↗

arXiv1997

Electromagnetic Mass Difference of Heavy Mesons

Using the Cottingham formula, we give an estimate of the electromagnetic mass splitting of pseudoscalar heavy mesons in the beauty and charm sector. We include in the dispersion relation the Born term, the $1^-$ resonance and the positive parity $1^+$ resonance. We also evaluate the contribution to the mass difference from the isospin breaking quark mass differences. Our results: $m_{B^+}-m_{B^0} = - 0.83\pm 0.34 MeV$ and $m_{D^+}-m_{D^0} = + 4.33\pm 0.37 MeV$, are in agreement with the experimental measurements: $m_{B^+}-m_{B^0} = - 0.35\pm 0.29 MeV$ and $m_{D^+}-m_{D^0} = + 4.78\pm 0.10 MeV$. We also compute the mass differences in the infinite heavy quark mass limit, which show small deviations from the finite mass results for the B case and 30% effects in the charm case.

hep-ph↗