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It has been argued that supergravity models of inflation with vanishing sound speeds, $c_s$, lead to an unbounded growth in the production rate of gravitinos. We consider several models of inflation to delineate the conditions for which $c_s = 0$. In models with unconstrained superfields, we argue that the mixing of the goldstino and inflatino in a time-varying background prevents the uncontrolled production of the longitudinal modes. This conclusion is unchanged if there is a nilpotent field associated with supersymmetry breaking with constraint ${bf S^2} =0$, i.e. sgoldstino-less models. Models with a second orthogonal constraint, ${bf S(Phi-bar{Phi})} =0$, where $bf{Phi}$ is the inflaton superfield, which eliminates the inflatino, may suffer from the over-production of gravitinos. However, we point out that these models may be problematic if this constraint originates from a UV Lagrangian, as this may require using higher derivative operators. These models may also exhibit other pathologies such as $c_s > 1$, which are absent in theories with the single constraint or unconstrained fields.
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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.
Gravitinos are a fundamental prediction of supergravity, their mass ($m_{G}$) is informative of the value of the SUSY breaking scale, and, if produced during reheating, their number density is a function of the reheating temperature ($T_{text{rh}}$). As a result, constraining their parameter space provides in turn significant constraints on particles physics and cosmology. We have previously shown that for gravitinos decaying into photons or charged particles during the ($mu$ and $y$) distortion eras, upcoming CMB spectral distortions bounds are highly effective in constraining the $T_{text{rh}}-m_{G}$ space. For heavier gravitinos (with lifetimes shorter than a few $times10^6$ sec), distortions are quickly thermalized and energy injections cause a temperature rise for the CMB bath. If the decay occurs after neutrino decoupling, its overall effect is a suppression of the effective number of relativistic degrees of freedom ($N_{text{eff}}$). In this paper, we utilize the observational bounds on $N_{text{eff}}$ to constrain gravitino decays, and hence provide new constaints on gravitinos and reheating. For gravitino masses less than $approx 10^5$ GeV, current observations give an upper limit on the reheating scale in the range of $approx 5 times 10^{10}- 5 times 10^{11}$GeV. For masses greater than $approx 4 times 10^3$ GeV they are more stringent than previous bounds from BBN constraints, coming from photodissociation of deuterium, by almost 2 orders of magnitude.
In this paper, we discuss interesting potential implications for the supersymmetric (SUSY) universe in light of cosmological problems on (1) the number of the satellite galaxies of the Milky Way (missing satellite problem) and (2) a value of the matter density fluctuation at the scale around 8$h^{-1}$Mpc ($S_{8}$ tension). The implications are extracted by assuming that the gravitino of a particular mass can be of help to alleviate the cosmological tension. We consider two gravitino mass regimes vastly separated, that is, $m_{3/2}simeq100{rm eV}$ and $m_{3/2}simeq100{rm GeV}$. We discuss non-trivial features of each supersymmetric universe associated with a specific gravitino mass by projecting potential resolutions of the cosmological problems on each of associated SUSY models.
We compute the effective potential for scalar fields in asymptotically safe quantum gravity. A scaling potential and other scaling functions generalize the fixed point values of renormalizable couplings. The scaling potential takes a non-polynomial form, approaching typically a constant for large values of scalar fields. Spontaneous symmetry breaking may be induced by non-vanishing gauge couplings. We strengthen the arguments for a prediction of the ratio between the masses of the top quark and the Higgs boson. Higgs inflation in the standard model is unlikely to be compatible with asymptotic safety. Scaling solutions with vanishing relevant parameters can be sufficient for a realistic description of particle physics and cosmology, leading to an asymptotically vanishing cosmological constant or dynamical dark energy.
Loop corrections to observables in slow-roll inflation are found to diverge no worse than powers of the log of the scale factor, extending Weinbergs theorem to quasi-single field inflation models. Demanding perturbation theory be valid during primordial inflation leads to constraints on the effective lagrangian. This leads to some interesting constraints and coincidences on the landscape of inflationary vacua.
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