iTHEMS Cosmology Forum n°1 - Cosmic birefringence and Parity Violation in the universe

Tuesday 14 May 2024, 09:30 → 18:00 Asia/Tokyo

435-437 Meeting Room (RIKEN Wako Campus)

iTHEMS Cosmology Forum Workshop is a series of short workshops, each focused on an emerging topics in cosmology. The targeted audience is cosmologists, high-energy physicists and astronomers interested in learning about the subject, not just those who have already worked on the topic. The goal of the workshop is to provide working knowledge of the topic and leave dedicated time for discussions to encourage mutual interactions among participants.

The first workshop is devoted to cosmic birefringence and parity violation in the Universe. Cosmic birefringence is a newly establishing cosmological probe of the nature of our universe. It refers to the rotation of the linear polarization plane of the cosmic microwave background (CMB) radiation and, thanks to its origin, inherently measures the degree of parity violation in the cosmic history. This one-day workshop gathers both the observational and theoretical aspects of this growing topic.

The workshop will be in English.

The workshops are organised by the iTHEMS Cosmology Forum working group, which is the successor of the Dark Matter Working Group at RIKEN iTHEMS.

Important dates:

30th April - Registration deadline 

14th May - Workshop Day

Invited Speakers:

Toshiya Namikawa (Kavli IPMU)

Maresuke Shiraishi (Suwa University of Science)

Fuminobu Takahashi (Tohoku University)

Organisers:

Kohei Hayashi, Nagisa Hiroshima, Derek Inman, Amaury Micheli, Ryo Namba

Support:

Limited support might be available for postdoc and non-permanent faculty members only. Please contact us directly.

09:30 → 10:30 Opening remarks and coffee

10:30 → 11:30 Tests for primordial parity symmetry - Observation Talk

Recent measurements of the CMB EB correlation and the imaginary galaxy trispectrum imply some parity-violating signals. These may originate from not only late-time axion phenomenology but also primordial one. Here, I would focus on the latter possibility, and talk about new findings and constraints on inflationary axion models from the above measurements, after reviewing primordial parity violation search so far.

Speaker: Maresuke Shiraishi

11:30 → 13:00 Lunch

13:00 → 14:30 Cosmic birefringence tomography - Keynote Talk

Cosmic birefringence --- a rotation of the linear polarization plane of the cosmic microwave background (CMB) as they travel through space --- is a key observational effect on CMB as it provides a way to search for parity-violating physics in cosmology. Recent measurements of the cross-correlation between the even-parity E-modes and odd-parity B-modes in the Planck polarization map suggest a tantalizing hint of cosmic birefringence. A possible candidate for the origin of cosmic birefringence is pseudoscalar ``axionlike'' fields. In this talk, after briefly reviewing the observations of isotropic and anisotropic cosmic birefringence, I will discuss the importance of the time evolution of axionlike fields to explore the origin of cosmic birefringence.

Speaker: Toshiya Namikawa (IPMU)

14:30 → 15:30 Discussion and coffee

15:30 → 16:30 Isotropic and anisotropic cosmic birefringence by axion domain walls - Theory Talk

The isotropic cosmic birefringence with a rotation angle of about 0.3 degrees has been suggested by the recent analysis of the CMB polarization data. The suggested rotation angle is tantalizingly close to the angle determined by the fine structure constant, 1/137 radians = 0.42 degrees. I will show that axion domain walls coupled to QED can naturally explain this coincidence for a wide range of axion masses and axion-photon couplings. Furthermore, the axion domain walls predict a characteristic anisotropic cosmic birefringence, which can be investigated by future observations and will tell us about the initial state of the axion fluctuations in the very early universe.

Speaker: Fuminobu Takahashi

16:30 → 18:00 Extended discussion and Closing remarks