Reassessing the link betweenB-modes and inflation

Abstract

We reevaluate the predictions of inflation regarding primordial gravity waves, which should appear as B-modes in the CMB, in light of the fact that the standard inflationary paradigm is unable to account for the transition from an initially symmetric state into a non-symmetric outcome. We show that the incorporation of an element capable of explaining such a transition dramatically alters the prediction for the shape and size of the B-mode spectrum. In particular, we find that by adapting a realistic objective collapse model to the situation at hand, the B-mode spectrum gets strongly suppressed with respect to the standard prediction. We conclude that the failure to detect B-modes in the CMB does not rule-out the simplest inflationary models.The exquisite matching between observations of temperature anisotropies in the CMB and the generic predictions of inflation provides a powerful justification for the recent consolidation of the inflationary paradigm as a cornerstone of modern cosmology. However, such a paradigm also makes predictions for the shape and amplitude of primordial gravity waves, which should be observable in the B-mode polarization of the CMB. The fact that, so far, such B-modes have not been observed, has been used to severely constrain the set of viable inflationary models [1][2][3]. Moreover, the recent detection of gravity waves by LIGO [4] removes all lingering doubts about the reality of such waves (if there were any remaining, given the dramatic indirect evidence provided by the Binary Pulsar studies [5]). This only increases the urgency to resolve the tension generated by the predictions regarding B-modes and our failure to detect them.As initially argued in [6], the standard inflationary account for the emergence of the primordial perturbations lacks a crucial element capable of accounting for the transition from the initially homogeneous and isotropic quantum state into a state lacking such symmetries. The objective of this letter is to show that the adoption of a framework that explicitly introduces this element drastically modifies the predictions for the shape and amplitude of the primordial gravity waves (without also altering confirmed predictions of inflation) [7]. As a result, we conclude that the impact of the B-polarization nullresults on the viability of various inflationary models has to be reexamined. In particular, we establish that, contrary to what has been argued, the failure to detect Bmodes in the CMB does not rule-out the simplest inflationary models.The crucial observation overlooked by the standard account is concerned with the way in which the quantum fluctuations of the completely homogeneous and isotropic state that characterizes the early stages of inflation (i.e., the Bunch-Davies vacuum or related states), are supposed to transform into actual inhomogeneities and anisotropies. The problem is that such "fluctuations" are nothing more than a characterization of the width of the wave function for the corresponding field degrees of freedom and not acutal, physical...

Constraining quantum collapse inflationary models with current data: The semiclassical approach

“…This view is quite natural once one considers, say the problem of time in canonical quantum gravity, and the regimes in which a notion of time might effectively emerge 6. For instance in[53,54] it was argued that when considering the spectrum at the end of inflation, it was natural to take a cutoff scale to be given by the last scale that exits the horizon during inflation. On the other hand, when one is interested in comparing the theoretical predictions with the data from the CMB, one must take into account plasma damping effects and thus introduce a cutoff scale corresponding to the scale of diffusion or Silk damping…”

Generation of inflationary perturbations in the continuous spontaneous localization model: The second order power spectrum

“…of order |α s | 10 −3 and the tensor-to-scalar ratio r remains undetected, then the hierarchy of the HFF would be broken and the standard slow roll inflationary model would be in some sense jeopardized. On the other hand, the CSLIM generically predicts a strong suppression of tensor modes, that is r 2 1 10 −12 [33,34]. And, since the function C(k) introduces an extra k dependence on the PS, the situation described previously, in principle, could not yield an inconsistency between the CSLIM and hierarchy of the HFF.…”

“…The CSLIM also predicts a strong suppression of primordial gravity waves, but in this case the tensor modes are generated by second order scalar perturbations [33,34]; in fact, an estimate for the tensor-to-scalar ratio has been obtained in Ref. [33]: r = 10 −7 2…”

“…Moreover, in [32][33][34], and working in the context of semiclassical gravity, it was shown that the CSLIM predicts a strong suppression of primordial B-modes, i.e. the predicted amplitude of the tensor power spectrum is very small generically (undetectable by current experiments).…”

Eternal inflation and the quantum birth of cosmic structure

“…The implementation of the CSL model into the picture of slow-roll inflation has been analyzed in previous work [42,[46][47][48] (in Refs. [43][44][45] the CSL model is also considered during inflation but based on a different conceptual approach).…”