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H. Rubinstein

Publications and source records attributed to H. Rubinstein.

4 recordsLinked to original sources
arXiv2008

Anisotropic fragmentation in low-energy dissociative recombination

On a dense energy grid reaching up to 75 meV electron collision energy the fragmentation angle and the kinetic energy release of neutral dissociative recombination fragments have been studied in a twin merged beam experiment. The anisotropy described by Legendre polynomials and the extracted rotational state contributions were found to vary on a likewise narrow energy scale as the rotationally averaged rate coefficient. For the first time angular dependences higher than 2$^{nd}$ order could be deduced. Moreover, a slight anisotropy at zero collision energy was observed which is caused by the flattened velocity distribution of the electron beam.

physics.atom-ph↗
arXiv2006

3-manifolds built from injective handlebodies

This paper looks at a class of closed orientable 3-manifolds constructed from a gluing of three handlebodies, such that the inclusion of each handlebody is $\pi_1$-injective. This construction is the generalisation to handlebodies of the condition for gluing three solid tori to produce non-Haken Seifert fibered 3-manifolds with infinite fundamental group. It is shown that there is an efficient algorithm to decide if a gluing of handlebodies meets the disk-condition. Also an outline for the construction of the characteristic variety (JSJ decomposition) in such manifolds is given. Some non-Haken and atoroidal examples are given.

math.GT↗
arXiv1999

Constraints on the Variation of the Fine Structure Constant from Big Bang Nucleosynthesis

We put bounds on the variation of the value of the fine structure constant $α$, at the time of Big Bang nucleosynthesis. We study carefully all light elements up to $^7$Li. We correct a previous upper limit on $|Δα/ α|$ estimated from $^4$He primordial abundance and we find interesting new potential limits (depending on the value of the baryon-to-photon ratio) from $^7$Li, whose production is governed to a large extent by Coulomb barriers. The presently unclear observational situation concerning the primordial abundances preclude a better limit than $|Δα/α| \lsim 2\cdot 10^{-2}$, two orders of magnitude less restrictive than previous bounds. In fact, each of the (mutually exclusive) scenarios of standard Big Bang nucleosynthesis proposed, one based on a high value of the measured deuterium primordial abundance and one based on a low value, may describe some aspects of data better if a change in $α$ of this magnitude is assumed.

astro-ph↗