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SUMMARY:Local Cosmography from Causal Set Pixies
DTSTART;VALUE=DATE-TIME:20261024T062000Z
DTEND;VALUE=DATE-TIME:20261024T064000Z
DTSTAMP;VALUE=DATE-TIME:20261025T040242Z
UID:indico-contribution-3005@indico.itp.ac.cn
DESCRIPTION:Speakers: He Liu (Tsinghua University)\nIn causal set theory\,
  spacetime is represented by a locally finite partially ordered set. The a
 bundances of small combinatorial structures can be used to recover informa
 tion about its continuum geometry. We study how chains and 2-pixies can be
  used to recover local cosmological quantities in four-dimensional\, spati
 ally flat FLRW spacetimes. For causal diamonds centered on a comoving obse
 rver\, we calculate the symmetric abundances through fourth order in the p
 roper duration and the difference between upward and downward 2-pixies thr
 ough third order. Riemann normal expansions identify the geometric terms\,
  and exact integration in conformal coordinates gives their coefficients. 
 The symmetric counts determine combinations of the Hubble and deceleration
  parameters. The difference between upward and downward 2-pixies probes cu
 rvature evolution and gives access to the dimensionless third derivative o
 f the scale factor\, known as the cosmological jerk. We test the calculati
 on with independent continuum integration and simulated causal sets\, and 
 study the inference using the full covariance of the counts. The tests sep
 arate geometric truncation error from sampling uncertainty and show the co
 st of including higher-order terms. The construction uses calibrated inter
 val durations. Applying it within one causal set requires an intrinsic clo
 ck and a treatment of correlations between overlapping intervals.\n\nhttps
 ://indico.itp.ac.cn/event/427/contributions/3005/
LOCATION:
URL:https://indico.itp.ac.cn/event/427/contributions/3005/
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