Comment to: Corrections to the fine structure constant in the spacetime of a cosmic string from the generalized uncertainty principle

In the paper [F. Nasseri, Phys. Lett. B 632 (2006) 151--154], F. Nasseri supposed that the value of the angular momentum for the Bohr's atom in the presence of the cosmic string is quantized in units of ℏ. Using this assumption it was obtained an incorrect expression for Bohr radius in this scenario. In this comment I want to point out that this assumption is not correct and present a corrected expression for the Bohr radius in this background.Comment: This paper was published in Phys. Lett.

T-duality and α′\alpha'-corrections

We construct an $O(d,d)$ invariant universal formulation of the first-order $\alpha'$-corrections of the string effective actions involving the dilaton, metric and two-form fields. Two free parameters interpolate between four-derivative terms that are even and odd with respect to a $Z_2$-parity transformation that changes the sign of the two-form field. The $Z_2$-symmetric model reproduces the closed bosonic string, and the heterotic string effective action is obtained through a $Z_2$-parity-breaking choice of parameters. The theory is an extension of the generalized frame formulation of Double Field Theory, in which the gauge transformations are deformed by a first-order generalized Green-Schwarz transformation. This deformation defines a duality covariant gauge principle that requires and fixes the four-derivative terms. We discuss the $O(d,d)$ structure of the theory and the (non-)covariance of the required field redefinitions.Comment: 35 pages, v2: Minor corrections, published in JHE

Identification of fullerene-like CdSe nanoparticles from optical spectroscopy calculations

Semiconducting nanoparticles are the building blocks of optical nanodevices as their electronic states, and therefore light absorption and emission, can be controlled by modifying their size and shape. CdSe is perhaps the most studied of these nanoparticles, due to the efficiency of its synthesis, the high quality of the resulting samples, and the fact that the optical gap is in the visible range. In this article, we study light absorption of CdSe nanostructures with sizes up to 1.5 nm within density functional theory. We study both bulk fragments with wurtzite symmetry and novel fullerene-like core-cage structures. The comparison with recent experimental optical spectra allows us to confirm the synthesis of these fullerene-like CdSe clusters

The planar-to-tubular structural transition in boron clusters from optical absorption

The optical response of the lowest energy isomers of the B_20 family is calculated using time-dependent density functional theory within a real-space, real-time scheme. Significant differences are found among the absorption spectra of the clusters studied. We show that these differences can be easily related to changes in the overall geometry. Optical spectroscopy is thus an efficient tool to characterize the planar to tubular structural transition, known to be present in these boron based systems

Clustering and Correlations at the Neutron Dripline

Some recent experimental studies of clustering and correlations within very neutron-rich light nuclei are reviewed. In particular, the development of the novel probes of neutron-neutron interferometry and Dalitz-plot analyses is presented through the example of the dissociation of the two-neutron halo system $^{14}$Be. The utility of high-energy proton radiative capture is illustrated using a study of the $^{6}$He(p,$\gamma$) reaction. A new approach to the production and detection of bound neutron clusters is also described, and the observation of events with the characteristics expected for tetraneutrons ($^{4}$n) liberated in the breakup of $^{14}$Be is discussed. The prospects for future work, including systems beyond the neutron dripline, are briefly outlined.Comment: Invited contribution to a topical issue on Exotic Nuclei of Les Comptes Rendus de l'Academie des Sciences Paris, Serie IV. 29 pages,11 figures (format RevTex preprint