Experimental bounds on the coupling strength of torsion potentials

We examine the experimental implications of a recent suggestion by Kaempffer that the coupling strength $G^{\prime }$ for a propagating torsion potential need not be the same as the Newtonian gravitational coupling strength $G$. We allow the torsion potential to transform either as a six-tensor, or as a pseudoscalar. In neutrino-electron and neutrino-nucleon scattering, we find that pseudoscalar exchange does not contribute, while exchange of the six-tensor closely simulates exchange of a $Z^0$. Agreement of data with Weinberg-Salam neutral current theory is preserved if $4\pi G^{\prime }<0.14\mathrm{}\frac{G_F{c}^2}{{\hslash }^2}$, where $G_F$ is the Fermi $\mu$ decay constant. If we demand that emission of torsion quanta not destroy the energy balance in helium-burning stars, we get a much stronger bound $4\pi G^{\prime }<5\mathrm{}\times {10}^{-19\mathrm{}}\frac{G_F{c}^2}{{\hslash }^2}$. This bound applies to both cases, pseudoscalar as well as six-tensor. It may be rewritten $G^{\prime }<\frac{1}{{(1.5\mathrm{}\times {10}^{12} \mathrm{GeV})}^2}$ in natural units. For comparison, $G=\frac{1}{{(1.2\mathrm{}\times {10}^{19} \mathrm{GeV})}^2}$.