IPTA DR2 Search

for Cosmic Strings

Meeting #07, June 16, 2022, 15:00 UTC

Participants

Kai Schmitz

Ken Olum

Andrea Mitridate

Jeremy Wachter

Jose J. Blanco-Pillado

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Nihan Pol

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Alexander Bonilla

William Lamb

Tobias Schröder

Agenda

1. Kai: New (final!) data sets
2. Andrea: New runs
3. Next steps
4. Alexander: New ideas
5. Questions, comments

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Mainz workshop 2023 (Approved!)

Pulsar Timing Arrays: A star-way to new physics

• Bring together PTA and BSM experts
• When: August 14-18 2023
• Where: https://www.mitp.uni-mainz.de
• Contact: vedranbrdar@gmail.com

New data sets based on the VOS model (Kai)

https://drive.google.com/drive/folders/1JgpiZ9bAHjngK20neqS6rdUYaur3hu97?usp=sharing

Stable strings: stable.dat

log10(Gmu) = -14 … -1.5, 7686 data points, excellent agreement with Ken’s data

Metastable strings (loops): meta_l.dat

log10(Gmu) = -14 … -1.5, sqrt(kappa) = 7.0…9.5, 80886 data points

Metastable strings (loops + segments): meta_l+s.dat

log10(Gmu) = -14 … -1.5, sqrt(kappa) = 7.0…9.5, 80886 data points

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Models:

1. Common-spectrum process, single power law, spectral index 13/3
2. SMBHBs
3. Stable
4. MetaL
5. MetaLS
6. SMBHBs + Stable
7. SMBHBs + MetaL
8. SMBHBs + MetaLS

Cosmic superstrings???

Runs with IPTA DR2 (Andrea)

log₁₀(BF) ~ -0.58

Stable

Comparison with previous runs

Meeting #03, NG12.5

Meeting #04, ???

Meeting #07, IPTA DR2

Runs with IPTA DR2 (Andrea)

log₁₀(BF) ~ -0.35

MetaL: metastable (loops)

log₁₀(BF) ~ -0.27

MetaLS: metastable (loops + segments)

Comparison with previous runs

Meeting #06

Meeting #07

Exactly the same data in the “stable strings” region of parameter space; still slightly different posterior distribution. (?)

Comparison with 2107.04578

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Consider, e.g., Gmu = 10^-7 and sqrt(kappa) = 8.1

• MetaL (left) yields slightly better fit than MetaLS (right)
• This is because segments can yield a slightly flatter spectrum (smaller spectral index)
• Consistent with Andrea’s findings: MetaL fit slightly better for this benchmark point

Next steps

1) Why do our posteriors change even though the data is the same as before?

Next steps

2) Can we capture the full 95% posterior regions, i.e., go to large Gmu, small sqrt(kappa)?

Next steps

3) How are we going to cross check our results? More independent runs? Nihan, Paul, Siyuan, Tobias? Anyone else with ENTERPRISE experience?

Next steps

4) Explicitly check transitivity of Bayes factors! Need more people running code?

Next steps

5) Do we want to include cosmic superstrings? Let’s have a poll!

Simple 1/P rescaling or Masaki Yamada’s approach? https://arxiv.org/abs/2204.13125 https://arxiv.org/abs/2204.13123 Homework: Carefully check whether Masaki’s “extended VOS model” really just results in a 1/P rescaling (1/P_eff rescaling), or whether there is something else. → Kai + someone else?

Next steps

6) Start writing the draft! Kai: VOS model, stable and metastable strings, signal prediction. Andrea: Preliminary plots

Questions

Q1: Include GWs from segments? Study both: loops / loops + segments?

Typical GUT symmetry breaking pattern, leads to monopoles with flux:

SU(2) x U(1) → U(1) x U(1) → U(1) (Buchmuller, https://arxiv.org/abs/2102.08923)

E.g. SO(10) → SU(4) x SU(2) x SU(2) → SU(3) x SU(2) x U(1) x U(1)→SM

Monopoles without flux would require:

SU(2) → U(1) → nothing

GUT example ???

Questions

Q2: Treat stable strings independently, or as limiting case of metastable strings?

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1. Introduction
2. Stable cosmic strings
3. Exotic models

3a) Metastable strings

3b) Cosmic superstrings

Questions

Q3: How many Bayes factors do we want to determine? 7, 5, 3?

Questions

Q4: Which parameter ranges do we want to scan over?

log10 (G\mu) = -14 … -6

kappa = 58 … 90 (sqrt(kappa) = 7.6 … 9.5)

Questions

Q5: Any other comments / suggestions? Does this fix the setup of our final runs? Any other scans we want to perform for our paper? Are we ready to start writing the paper once we are done with our final runs for models 1, 2, 3, …, 8?

New ideas (Alexander)

Any other business

Next meeting on July 7, 2022 at 15:00 UTC?