Constraining single-field inflation with MegaMapper

Local primordial non-Gaussianity (LPNG) is predicted by many non-minimal models of inflation, and creates a scale-dependent contribution to the power spectrum of large-scale structure (LSS) tracers, whose amplitude is characterized by bϕ . Knowledge of bϕ for the observed tracer population is therefore crucial for learning about inflation from LSS. Recently, it has been shown that the relationship between linear bias b1 and bϕ for simulated halos exhibits significant secondary dependence on halo concentration. We leverage this fact to forecast multi-tracer constraints on f loc NL. We train a machine learning model on observable properties of simulated IllustrisTNG galaxies to predict bϕ for samples constructed to approximate DESI emission line galaxies (ELGs) and luminous red galaxies (LRGs). We find σ(f loc NL) = 2.3, and σ(f loc NL = 3.7, respectively. These forecasted errors are roughly factors of 3, and 35% improvements over the single-tracer case for each sample, respectively. When considering both ELGs and LRGs in their overlap region, we forecast σ(f loc NL) = 1.5 is attainable with our learned model, more than a factor of 3 improvement over the single-tracer case, while the ideal split by bϕ could reach σ(f loc NL) < 1. We also perform multi-tracer forecasts for upcoming spectroscopic surveys targeting LPNG (MegaMapper, SPHEREx) and show that splitting tracer samples by bϕ can lead to an order-of-magnitude reduction in projected σ(f loc NL for these surveys.

Section: Forecast Setupmentioning

confidence: 99%

Learning to concentrate: multi-tracer forecasts on local primordial non-Gaussianity with machine-learned bias

Sullivan

Prijon

Seljak

2023

“…The study of cosmological inhomogeneities evolving in a symmetric background plays a crucial role in our current understanding of the primordial universe from pioneering works [1][2][3][4][5][6][7][8][9][10][11][12][13][14] to latest observations [58][59][60][61][62][63][122][123][124][125][126]. The dynamics of the background is imprinted in the evolution of the fluctuations which can be used as tracers of the geometry [127][128][129].…”

Section: Two-field Primordial Universe Modelsmentioning

confidence: 99%

Decoherence out of fire: purity loss in expanding and contracting universes

Colas,

de Rham,

Kaplanek

2024

We investigate quantum decoherence in a class of models which interpolates between expanding (inflation) and contracting (ekpyrosis) scenarios. For the cases which result in a scale-invariant power spectrum, we find that ekpyrotic universes lead to complete decoherence of the curvature perturbation before the bounce. This is in stark contrast to the inflationary case, where recoherence has been previously observed in some situations. Although the purity can be computed for couplings of all sizes, we also study the purity perturbatively and observe that late-time (secular growth) breakdown of perturbation theory often occurs in these cases. Instead, we establish a simple yet powerful late-time purity resummation which captures the exact evolution to a remarkable level, while maintaining analytical control. We conclude that the cosmological background plays a crucial role in the decoupling of the heavy fields during inflation and alternatives.

“…In this limit, it is possible to extend the WKB solution for χ to include effects of φ. 12 Then, one can use it to compute δO R by expanding the expectation value of O to linear order in φ. Note that the particular form of the kernel depends crucially on the structure of the operator in terms of χ, i.e., the five different combinations listed above.…”

Section: Jcap08(2023)076mentioning

confidence: 99%

“…The possibility that perturbations are generated by a scalar field different from the inflaton will be tested by local non-Gaussianities [5][6][7], once the threshold f loc NL ∼ 1 is reached (see for example [8][9][10]). Equilateral non-Gaussianities will be able to test whether the inflaton perturbations travel subluminally [11], although reaching f eq NL ∼ 1 will require more patience (see for example [9,12]).…”

Section: Introductionmentioning

confidence: 99%

Dissipative inflation via scalar production

Creminelli,

Kumar,

Salehian

et al. 2023

We describe a new mechanism that gives rise to dissipation during cosmic inflation. In the simplest implementation, the mechanism requires the presence of a massive scalar field with a softly-broken global U(1) symmetry, along with the inflaton field. Particle production in this scenario takes place on parametrically sub-horizon scales, at variance with the case of dissipation into gauge fields. Consequently, the backreaction of the produced particles on the inflationary dynamics can be treated in a local manner, allowing us to compute their effects analytically. We determine the parametric dependence of the power spectrum which deviates from the usual slow-roll expression. Non-Gaussianities are always sizeable whenever perturbations are generated by the noise induced by dissipation: f NL eq ≳ O(10).