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Dear all,<br>
<br>
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
(<a class="moz-txt-link-freetext" href="https://stockholmuniversity.zoom.us/j/62211269644?pwd=K0J2eVVMa3pTa1JVN2lyRUJPR3Rjdz09">https://stockholmuniversity.zoom.us/j/62211269644?pwd=K0J2eVVMa3pTa1JVN2lyRUJPR3Rjdz09</a>).<br>
___________________<br>
<br>
Speaker: Yutong He (Stockholm University)<br>
Title: Cosmological gravitational waves and their interaction with
large-scale magnetic fields<br>
Event: <a href="https://indico.fysik.su.se/e/yutong_he"
class="js-copy-to-clipboard moz-txt-link-freetext"
data-clipboard-text="https://indico.fysik.su.se/e/yutong_he"
data-clipboard-action="copy"
data-qtip-oldtitle="Copy link to clipboard">https://indico.fysik.su.se/e/yutong_he
</a><br>
<br>
Abstract:<br>
Gravitational waves (GWs) and magnetic fields are two essential
topics of cosmology. They interact in different ways in the early
and late Universe.<br>
<br>
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.<br>
<br>
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.<br>
<br>
___________________<br>
<br>
We look forward to seeing many of you there. Thanks!<br>
<br>
Adur, Adélaïde, and Sanja<br>
<br>
Upcoming Events:<br>
<br>
2024-04-12 Alex Riley<br>
2024-04-19 Arthur Choplin<br>
2024-04-26 Dominique Petit<br>
2024-05-03 Gang Li<br>
2024-05-08 Ivo (**Seminar on WEDNESDAY**)<br>
2024-05-10 Ray Jayawardhana (**Seminar on KLÄMDAG**)<br>
2024-05-14 Gayathri Viswanath (**Seminar on TUSDAY**)<br>
2024-05-17 Elena Khomenko<br>
<br>
You can subscribe to the seminars calendar in:<br>
<a class="moz-txt-link-freetext" href="https://ttt.astro.su.se/ical/astro-seminars.ics">https://ttt.astro.su.se/ical/astro-seminars.ics</a><br>
(Please note that calendar can be subject to updates)<br>
___________________<br>
<br>
Join Zoom Meeting:<br>
<a class="moz-txt-link-freetext" href="https://stockholmuniversity.zoom.us/j/62211269644?pwd=K0J2eVVMa3pTa1JVN2lyRUJPR3Rjdz09">https://stockholmuniversity.zoom.us/j/62211269644?pwd=K0J2eVVMa3pTa1JVN2lyRUJPR3Rjdz09</a><br>
Meeting ID: 622 1126 9644 <br>
<br>
<br>
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