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We study the possibility that primordial magnetic fields generated in thetransition between inflation and reheating posses magnetic helicity, $H_M$. Thefields are induced by stochastic currents of scalar charged particles createdduring the mentioned transition. We estimate the rms value of the inducedmagnetic helicity by computing different four-point SQED Feynman diagrams. Forany considered volume, the magnetic flux across its boundaries is in principlenon null, which means that the magnetic helicity in those regions is gaugedependent. We use the prescription given by Berger and Field and interpret ourresult as the difference between two magnetic configurations that coincide inthe exterior volume. In this case the magnetic helicity gives only the numberof magnetic links inside the considered volume. We calculate a concrete valueof $H_M$ for large scales and analyze the distribution of magnetic defects as afunction of the scale. Those defects correspond to regular as well as randomfields in the considered volume. We find that the fractal dimension of thedistribution of topological defects is $D = 1/2$. We also study if the regularfields induced on large scales are helical, finding that they are and that theassociated number of magnetic defects is independent of the scale. In this casethe fractal dimension is $D=0$. We finally estimate the intensity of fieldsinduced at the horizon scale of reheating, and evolve them until the decouplingof matter and radiation under the hypothesis of inverse cascade of magnetichelicity. The resulting intensity is high enough and the coherence length longenough to have an impact on the subsequent process of structure formation.

Primordial Magnetic Helicity from Stochastic Electric Currents