Kavli Affiliate: Jeffrey J. McMahon
| First 5 Authors: , , , ,
| Summary:
Deviations of the cosmic microwave background (CMB) energy spectrum from a
perfect blackbody uniquely probe a wide range of physics, ranging from
fundamental physics in the primordial Universe ($mu$-distortion) to late-time
baryonic feedback processes ($y$-distortion). While the $y$-distortion can be
detected with a moderate increase in sensitivity over that of COBE/FIRAS, the
$Lambda$CDM-predicted $mu$-distortion is roughly two orders of magnitude
smaller and requires substantial improvements, with foregrounds presenting a
serious obstacle. Within the standard model, the dominant contribution to $mu$
arises from energy injected via Silk damping, yielding sensitivity to the
primordial power spectrum at wavenumbers $k approx 1-10^4$ Mpc$^-1$. Here,
we present a new instrument concept, SPECTER, with the goal of robustly
detecting $mu$. The instrument technology is similar to that of LiteBIRD, but
with an absolute temperature calibration system. Using a Fisher approach, we
optimize the instrument’s configuration to target $mu$ while marginalizing
over foreground contaminants. Unlike Fourier-transform-spectrometer-based
designs, the specific bands and their individual sensitivities can be
independently set in this instrument, allowing significant flexibility. We
forecast SPECTER to observe the $Lambda$CDM-predicted $mu$-distortion at
$approx 5sigma$ (10$sigma$) assuming an observation time of 1 (4) year(s)
(corresponding to mission duration of 2 (8) years), after foreground
marginalization. Our optimized configuration includes 16 bands spanning 1-2000
GHz with $sim$degree-scale angular resolution at $sim150$ GHz and 1100 total
detectors. SPECTER will additionally measure the $y$-distortion at sub-percent
precision and its relativistic correction at percent-level precision, yielding
tight constraints on the total thermal energy and mean temperature of ionized
gas.
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