Catastrophic Production of Slow Gravitinos. (arXiv:2102.10113v1 [hep-th])

<a href="http://arxiv.org/find/hep-th/1/au:+Kolb_E/0/1/0/all/0/1">Edward W. Kolb</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Long_A/0/1/0/all/0/1">Andrew J. Long</a>, <a href="http://arxiv.org/find/hep-th/1/au:+McDonough_E/0/1/0/all/0/1">Evan McDonough</a>

We study gravitational particle production of the massive spin-$3/2$

Rarita-Schwinger field, and its close relative, the gravitino, in FRW

cosmological spacetimes. For masses lighter than the value of the Hubble

expansion rate after inflation, $m_{3/2} lesssim H$, we find catastrophic

gravitational particle production, wherein the number of gravitationally

produced particles is divergent, caused by a transient vanishing of the

helicity-1/2 gravitino sound speed. In contrast with the conventional gravitino

problem, the spectrum of produced particles is dominated by those with momentum

at the UV cutoff. This suggests a breakdown of effective field theory, which

might be cured by new degrees of freedom that emerge in the UV. We study the UV

completion of the Rarita-Schwinger field, namely ${cal N}=1$, $d=4$,

supergravity. We reproduce known results for models with a single superfield

and models with an arbitrary number of chiral superfields, find a simple

geometric expression for the sound speed in the latter case, and extend this to

include nilpotent constrained superfields and orthogonal constrained

superfields. We find supergravity models where the catastrophe is cured and

models where it persists. Insofar as quantizing the gravitino is tantamount to

quantizing gravity, as is the case in any UV completion of supergravity, the

models exhibiting catastrophic production are prime examples of 4-dimensional

effective field theories that become inconsistent when gravity is quantized,

suggesting a possible link to the Swampland program. We propose the Gravitino

Swampland Conjecture, which is consistent with and indeed follows from the KKLT

and Large Volume scenarios for moduli stabilization in string theory.

We study gravitational particle production of the massive spin-$3/2$

Rarita-Schwinger field, and its close relative, the gravitino, in FRW

cosmological spacetimes. For masses lighter than the value of the Hubble

expansion rate after inflation, $m_{3/2} lesssim H$, we find catastrophic

gravitational particle production, wherein the number of gravitationally

produced particles is divergent, caused by a transient vanishing of the

helicity-1/2 gravitino sound speed. In contrast with the conventional gravitino

problem, the spectrum of produced particles is dominated by those with momentum

at the UV cutoff. This suggests a breakdown of effective field theory, which

might be cured by new degrees of freedom that emerge in the UV. We study the UV

completion of the Rarita-Schwinger field, namely ${cal N}=1$, $d=4$,

supergravity. We reproduce known results for models with a single superfield

and models with an arbitrary number of chiral superfields, find a simple

geometric expression for the sound speed in the latter case, and extend this to

include nilpotent constrained superfields and orthogonal constrained

superfields. We find supergravity models where the catastrophe is cured and

models where it persists. Insofar as quantizing the gravitino is tantamount to

quantizing gravity, as is the case in any UV completion of supergravity, the

models exhibiting catastrophic production are prime examples of 4-dimensional

effective field theories that become inconsistent when gravity is quantized,

suggesting a possible link to the Swampland program. We propose the Gravitino

Swampland Conjecture, which is consistent with and indeed follows from the KKLT

and Large Volume scenarios for moduli stabilization in string theory.

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