The Future of Primordial Features with Large-Scale Structure Surveys

TL;DR

This work forecasts the detectability of primordial feature signals with forthcoming large-scale structure surveys, classifying models into sharp features, resonance features, standard clocks, and bumps, and using simple templates to capture the essential physics. By performing Fisher-m matrix forecasts that incorporate linear galaxy clustering, redshift-space distortions, and survey characteristics for LSST-like photometric and Euclid-like spectroscopic data, the authors show that 3D LSS data can substantially improve Planck constraints on oscillatory features, often by a factor of 5 or more, especially for high-frequency models. They find complementary strengths between Euclid and LSST, with Euclid excelling in amplitude constraints and LSST in constraining detailed feature parameters, while clock signals remain a particularly powerful probe of the background expansion history. The results underscore the significant potential of next-generation LSS surveys to illuminate the physics of the primordial universe, motivate cross-checks with CMB polarization and non-Gaussianity, and guide future refinements including non-linear modeling and 21 cm probes.

Abstract

Primordial features are one of the most important extensions of the Standard Model of cosmology, providing a wealth of information on the primordial universe, ranging from discrimination between inflation and alternative scenarios, new particle detection, to fine structures in the inflationary potential. We study the prospects of future large-scale structure (LSS) surveys on the detection and constraints of these features. We classify primordial feature models into several classes, and for each class we present a simple template of power spectrum that encodes the essential physics. We study how well the most ambitious LSS surveys proposed to date, including both spectroscopic and photometric surveys, will be able to improve the constraints with respect to the current Planck data. We find that these LSS surveys will significantly improve the experimental sensitivity on features signals that are oscillatory in scales, due to the 3D information. For a broad range of models, these surveys will be able to reduce the errors of the amplitudes of the features by a factor of 5 or more, including several interesting candidates identified in the recent Planck data. Therefore, LSS surveys offer an impressive opportunity for primordial feature discovery in the next decade or two. We also compare the advantages of both types of surveys.

Figures (12)

• Figure 1: Primordial sharp feature signal. Here we have set, $k_f [{\rm Mpc}^{-1}] = 0.004$ (upper-left), 0.03 (upper-right) and 0.1 (lower). For all plots we also have $C=0.03$ and $\phi=0$.
• Figure 2: Two examples of the sharp feature signals from the step-in-potential model (Eq. \ref{['Template:step']}). The left panel is a milder step (i.e. the step has relatively small height-to-width-ratio) with ${\cal{C}} = 0.218$, $\eta_f = 1.44$ Gpc and $x_d=1.6$. As we can see, the envelop of the sinusoidal running is very important for this case. The solid-blue line in the right panel is a sharper step (i.e. the step has relatively large height-to-width-ratio) with ${\cal{C}} = 0.033$, $\eta_f=0.25$ Gpc and $x_d=100$. As we can see, the envelop of the sinusoidal running is less important, and the simple template of Eq. \ref{['Template_Sharp']} (dashed-red line, $C=0.1$, $k_f=0.004/$ Mpc and $\phi=\pi/2$) is a good approximation in this case.
• Figure 3: The resonance feature in the power spectrum, as in Eq. \ref{['Template_Resonance']}. For all three figures we have set $C=0.03$ and $\phi=0$, while for the upper-left, upper-right and lower plots we have $\Omega=5, 30$, and $100$, respectively.
• Figure 4: The clock signal for alternative scenarios (Eq.\ref{['Template:clock']} with ($-1<p<1$)). We have set $C=0.05$, $k_r=0.1/$Mpc, $\Omega_{\rm eff}= 100$, $\phi=0$, and $p=2/3$ (upper-left panel), $1/5$ (upper-right panel) and $-1/5$ (lower panel).
• Figure 5: The clock signal for inflationary scenarios (Eq.\ref{['Template:inf_clock']}) with $k_r=0.10753/$Mpc, $p=105$, $\Omega_{\rm eff}= 59.1$, $\phi=2.15$, and $C=0.0576$.