Posts

Day 1 This question is about finding the first and last “digit” which could be written as number or word and computing the sum over all input lines. My attempt with julia: digits_lookup = Dict( "0" => 0, "1" => 1, "2" => 2, "3" => 3, "4" => 4, "5" => 5, "6" => 6, "7" => 7, "8" => 8, "9" => 9, "zero" => 0, "one" => 1, "two" => 2, "three" => 3, "four" => 4, "five" => 5, "six" => 6, "seven" => 7, "eight" => 8, "nine" => 9 ) function parse_number(line) out, digit = 0, 0 for i in eachindex(line) for (k, v) in digits_lookup if line[i:min(i+length(k)-1, length(line))] == k digit = v break end end out = out > 0 ?...

Gauge in Cosmology (2023/11/14) Why is there gauge freedom when analyzing cosmological perturbations? I think this lies in the fact that our background universe is homogeneous and isotropic, and density perturbations are perturbatively small. An observer in FLRW effectively experiences no gravity in the background level and thus has no preferred inertial frame background universe. The observer thus has the freedom to choose an inertial frame, as long as it doesn’t violate the perturbation limit, to describe his observable universe, and this introduces the gauge freedom....

A repository to keep track of random little things I learned or thought about each day. The Cosmic Dipole Problem (2023/11/29) CMB features a dipole anisotropy which is interpreted as our motion relative to the cosmic rest frame. If this interpretation is correct, one expects other probe of this relative motion to feature the same cosmic dipole. However measurements from radio galaxies and quasars have presented some discrepancies in the magnitude of the cosmic dipole (see, e....

Isotropic Methods Minami et al. 2019: describes a method to simutaneously determine birefringence and detector miscalibration using galactic foreground emission, assuming the galactic foreground has zero EB correlation. Sherwin and Namikawa 2021: miscalibration free measurements of isotropic birefringence using reionization bump. Namikawa 2021: use CMB mode coupling to constrain isotropic birefringence. Lee, Hotinli, and Kamionkowski 2022: use polarized SZ effect to probe cosmic birefringence. Diego-Palazuelos, Mart\’ınez-González, et al. 2022: validate method of (Minami et al....