UV/IR mode mixing and the CMB

TL;DR

This paper explores how UV/IR mode mixing in non-commutative field theories can significantly suppress CMB power spectrum, providing constraints on the non-commutativity scale through inflationary cosmology.

Contribution

It demonstrates that UV/IR mode mixing in non-commutative theories can impose strong constraints on non-commutativity using CMB observations, regardless of inflation scale.

Findings

Non-commutativity suppresses CMB power at all observable scales.

UV/IR mixing effects are independent of inflation scale.

Constraints on non-commutativity are derived from CMB data.

Abstract

It is well understood that spatial non-commutativity, if indeed realized in nature, is a phenomenon whose effects are not just felt at energy scales comparable to the non-commutativity scale. Loop effects can transmit signatures of any underlying non-commutativity to macroscopic scales (a manifestation of a phenomenon that has come to be known as UV/IR mode mixing) and offer a potential lever to constrain the amount of non-commutativity present in nature, if present at all. Field theories defined on non-commutative spaces (realized in string theory when D-branes are coupled to backgrounds of non-trivial RR background flux), can exhibit strong UV/IR mode mixing, manifesting in a non-local one loop effective action. In the context of inflation in the presence of any background non-commutativity, we demonstrate how this UV/IR mixing at the loop level can allow us to place severe constraints on the scale of non-commutativity if we presume inflation is responsible for large scale structure. We demonstrate that any amount of non-commutativity greatly suppresses the CMB power at all observable scales, {\it independent} of the scale of inflation, and independent of whether or not the non-commutativity tensor redshifts during inflation, therefore nullifying a very salient and successful prediction of inflation.