Finite inflation in curved space

Hergt, L. T.; Agocs, F. J.; Handley, Will; Hobson, M. P.; Lasenby, A.

doi:10.1103/physrevd.106.063529

Cited by 12 publications

(6 citation statements)

References 111 publications

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“…Other models that can violate the above properties of vacuum-produced GW background are those introducing non-minimal coupling of the inflaton [49][50][51], additional scalar fields [52][53][54][55][56], and modified gravity models [57]. Non-zero spatial curvature and kinetically-dominated initial conditions for inflation could also play a role in amplification or suppression of the GW background [58,59].…”

mentioning

confidence: 99%

Measuring the spectrum of primordial gravitational waves with CMB, PTA and laser interferometers

Campeti

Komatsu

Poletti

et al. 2021

J. Cosmol. Astropart. Phys.

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We investigate the possibility of measuring the primordial gravitational wave (GW) signal across 21 decades in frequencies, using the cosmic microwave background (CMB), pulsar timing arrays (PTA), and laser and atomic interferometers. For the CMB and PTA experiments we consider the LiteBIRD mission and the Square Kilometer Array (SKA), respectively. For the interferometers we consider space mission proposals including the Laser Interferometer Space Antenna (LISA), the Big Bang Observer (BBO), the Decihertz Interferometer Gravitational wave Observatory (DECIGO), the µAres experiment, the Decihertz Observatory (DO), and the Atomic Experiment for Dark Matter and Gravity Exploration in Space (AEDGE), as well as the ground-based Einstein Telescope (ET) proposal. We implement the mathematics needed to compute sensitivities for both CMB and interferometers, and derive the response functions for the latter from the first principles. We also evaluate the effect of the astrophysical foreground contamination in each experiment. We

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confidence: 99%

Measuring the spectrum of primordial gravitational waves with CMB, PTA and laser interferometers

Campeti

Komatsu

Poletti

et al. 2021

J. Cosmol. Astropart. Phys.

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“…(1). Second, when |Ω K | becomes sizeable, it opens up a channel of backreaction of the curvature perturbation onto the background dynamics, which in turn alters the inflationary amplification of the curvature perturbations themselves [39,40]. This mechanism might be tractable in an extended stochastic-inflation formalism [41][42][43][44][45], which we plan to develop in a future work.…”

Section: Discussionmentioning

confidence: 99%

Spatial Curvature from Super-Hubble Cosmological Fluctuations

Blachier¹,

Auclair²,

Ringeval³

et al. 2023

Preprint

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We revisit how super-Hubble cosmological fluctuations induce, at any time in the cosmic history, a non-vanishing spatial curvature of the local background metric. The random nature of these fluctuations promotes the curvature density parameter to a stochastic quantity for which we derive novel non-perturbative expressions for its mean, variance, higher moments and full probability distribution. For scale-invariant Gaussian perturbations, such as those favored by cosmological observations, we find that the most probable value for the curvature density parameter ΩK today is −10 −9 , that its mean is +10 −9 , both being overwhelmed by a standard deviation of order 10 −5 . We then discuss how these numbers would be affected by the presence of large super-Hubble non-Gaussianities, or, if inflation lasted for a very long time. In particular, we find that substantial values of ΩK are obtained if inflation lasts for more than a billion e-folds.

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“…Certainly, there are inflationary models -by which we mean Lagrangians of field theories coupled to GR, 16 as opposed to our previous use of model to denote a choice of background manifold -that, for certain ranges of the Lagrangian parameters, take many cosmological initial conditions and map them into late-time universes in which certain spatial averages of the spatial Riemann tensor are small. For those models, parameter choices and initial conditions, the flat-FLRW metric, and thus Ω K = 0, is an attractor of the classical theory -given any patch of the early universe in which the initial conditions allow inflation to begin and in which there is a short-wavelength cutoff to the initial perturbation spectrum, then, ignoring quantum fluctuations, the Riemann tensor in that patch will be driven toward that of the flat-FLRW metric, and Ω K will be driven toward zero.…”

Section: Inflationary Model Priorsmentioning

confidence: 99%

“…In "just-so" inflationary models, this leads to Ω K arriving near 0, but to a value that may be observationally distinguishable from 0. Meanwhile, there are also inflationary models that predict Ω K = 0 for appropriate parameters [2,16] -such models were particularly popular when it was thought that Ω K = 0 and are once-again becoming of interest.…”

Section: Inflationary Model Priorsmentioning

confidence: 99%

“…However,[13] argued that for models[14,15] specifically constructed to give ΩK = 0 it is not, and even suggested that ns should not be included as a parameter for these models. Others[16] have argued for using parameters that characterize the kinematics of the inflationary period (eg. slow-roll parameters, or the number of e-folds) and avoiding entirely parameters, like ns that characterize a phenomenological or model-specific power-spectrum.…”

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confidence: 99%

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What is flat ΛCDM, and may we choose it?

Anselmi

Carney²,

Giblin

et al. 2023

J. Cosmol. Astropart. Phys.

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The Universe is neither homogeneous nor isotropic, but it is close enough that we can reasonably approximate it as such on suitably large scales. The inflationary-Λ-Cold Dark Matter (ΛCDM) concordance cosmology builds on these assumptions to describe the origin and evolution of fluctuations. With standard assumptions about stress-energy sources, this system is specified by just seven phenomenological parameters, whose precise relations to underlying fundamental theories are complicated and may depend on details of those fields. Nevertheless, it is common practice to set the parameter that characterizes the spatial curvature, Ω K , exactly to zero. This parameter-fixed ΛCDM is awarded distinguished status as separate model, “flat ΛCDM.” Ipso facto this places the onus on proponents of “curved ΛCDM” to present sufficient evidence that Ω K ≠ 0, and is needed as a parameter. While certain inflationary model Lagrangians, with certain values of their parameters, and certain initial conditions, will lead to a present-day universe well-described as containing zero curvature, this does not justify distinguishing that subset of Lagrangians, parameters and initial conditions into a separate model. Absent any theoretical arguments, we cannot use observations that suggest small Ω K to enforce Ω K = 0. Our track record in picking inflationary models and their parameters a priori makes such a choice dubious, and concerns about tensions in cosmological parameters and large-angle cosmic-microwave-background anomalies strengthens arguments against this choice. We argue that Ω K must not be set to zero, and that ΛCDM remains a phenomenological model with at least 7 parameters.

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Finite inflation in curved space

Cited by 12 publications

References 111 publications

Measuring the spectrum of primordial gravitational waves with CMB, PTA and laser interferometers

Measuring the spectrum of primordial gravitational waves with CMB, PTA and laser interferometers

Spatial Curvature from Super-Hubble Cosmological Fluctuations

What is flat ΛCDM, and may we choose it?

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