[Astronomy seminar] Astronomy departmental seminar Wednesday April 10 at 10:30am - Yutong He (Stockholm University)

[Astronomy seminar announcements]

Dear all,

The next SU astronomy departmental seminar will take place on Wednesday 
April 10 at 10:30am in room FC61 (AlbaNova building, 6th floor) and on 
zoom 
(https://stockholmuniversity.zoom.us/j/62211269644?pwd=K0J2eVVMa3pTa1JVN2lyRUJPR3Rjdz09).
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Speaker: Yutong He (Stockholm University)
Title: Cosmological gravitational waves and their interaction with 
large-scale magnetic fields
Event: https://indico.fysik.su.se/e/yutong_he 
<https://indico.fysik.su.se/e/yutong_he>

Abstract:
Gravitational waves (GWs) and magnetic fields are two essential topics 
of cosmology. They interact in different ways in the early and late 
Universe.

In the radiation era preceding the Cosmic Microwave Background (CMB), 
stochastic GW backgrounds (SGWBs) can be produced by magnetohydrodynamic 
(MHD) turbulence after the phase transitions at the electroweak (EW) and 
quantum chromodynamic (QCD) scales. We develop a general framework to 
study the SGWB spectrum in general relativity (GR) and modified gravity 
(MG) theories, with massive gravity and scalar-tensor theories as two 
examples. We then apply the framework to the MHD-GW system at the EW and 
QCD phase transitions to provide concrete constraints on effective MG 
parameters in light of ongoing and upcoming GW experiments, such as the 
Laser Interferometer Space Antenna (LISA) in the mHz band, and various 
pulsar timing array (PTA) collaborations in the nHz band.

In the post-CMB Universe, high-frequency GWs (HFGWs) propagating through 
large-scale magnetic fields have a probability of converting into 
photons of the same frequency. This conversion contributes to the 
distortion of blackbody CMB. Using the reported excess radio signals 
over the CMB, we place upper limits on the HFGW amplitude. We also 
forecast the capability of the Square Kilometer Array (SKA) and proposed 
future CMB surveys to significantly tighten the existing HFGW upper 
bounds in the MHz to THz frequency bands.

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We look forward to seeing many of you there. Thanks!

Adur, Adélaïde, and Sanja

Upcoming Events:

2024-04-12 Alex Riley
2024-04-19 Arthur Choplin
2024-04-26 Dominique Petit
2024-05-03 Gang Li
2024-05-08 Ivo (**Seminar on WEDNESDAY**)
2024-05-10 Ray Jayawardhana (**Seminar on KLÄMDAG**)
2024-05-14 Gayathri Viswanath (**Seminar on TUSDAY**)
2024-05-17 Elena Khomenko

You can subscribe to the seminars calendar in:
https://ttt.astro.su.se/ical/astro-seminars.ics
(Please note that calendar can be subject to updates)
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Join Zoom Meeting:
https://stockholmuniversity.zoom.us/j/62211269644?pwd=K0J2eVVMa3pTa1JVN2lyRUJPR3Rjdz09
Meeting ID: 622 1126 9644

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