Usually, a supersymmetry transformation is carried out on bosonic and fermionic fields which are functions of the coordinates (or on a superfield which is a function of real and fermionic coordinates). But, is it possible to interpret supersymmetry transformations as coordinate transformations on the set of coordinates (x0,…,xN,θ1,…,θM)?
The problem I see is that the coordinates would transform something like xμ→xμ+θσˉθ which is no longer a real (or complex) number, but a commuting Grassmann number. Can one make sens of a coordinate position no longer being a real number?
Edit: To clarify, this is NOT about confusion in what happens when adding real numbers with commuting grassmann numbers in general. That the lagrangian in QFT for example is not a real number, but a commuting grassmann number, is fine. What I am confused about is really how to make sense of coordinates that are grassmannian. Coordinates are supposed to describe a position in spacetime/on a manifold, and it seems to me that it is essential that a position is a standard real number.
Answer
Comments to the question (v3):
Recall that a supernumber z=zB+zS consists of a body zB (which always belongs to C) and a soul zS (which only belongs to C if it is zero), cf. e.g. this Phys.SE post.
An observable/measurable quantity can only consist of ordinary numbers (belonging to C). It does not make sense to measure a soul-valued output in an actual experiment.
Souls are indeterminates that appear in intermediate formulars, but are integrated (or differentiated) out in the final result.
In a superspace formulation of a field theory, a Grasmann-even spacetime coordinates xμ in superspace is promoted to a supernumber, and is not necessarily an ordinary number.
A supersymmetry-translation of a Grasmann-even spacetime coordinate xμ only changes the soul (but not the body) of xμ.
Note that in the mathematical definition of a supermanifold, the focus of the theory is not on spacetime coordinates per se, but (very loosely speaking) rather on certain algebras of functions of spacetime. See also e.g. Refs. 1-3 for details.
References:
Pierre Deligne and John W. Morgan, Notes on Supersymmetry (following Joseph Bernstein). In Quantum Fields and Strings: A Course for Mathematicians, Vol. 1, American Mathematical Society (1999) 41–97.
V.S. Varadarajan, Supersymmetry for Mathematicians: An Introduction, Courant Lecture Notes 11, 2004.
C. Sachse, A Categorical Formulation of Superalgebra and Supergeometry, arXiv:0802.4067.
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