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<span style="background-color: white;">Dear all, </span></div>
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On Monday, </span><span style="font-family: Calibri, Arial, Helvetica, sans-serif, serif, EmojiFont; font-size: 11pt; color: black; background-color: white;">April 15<sup>th</sup></span><span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; color: rgb(36, 36, 36); background-color: white;">,
2024 at 1pm </span><span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 14.67px; color: rgb(36, 36, 36); background-color: white;">EDT</span><span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; color: rgb(36, 36, 36); background-color: white;">,
we will have a </span><span style="font-family: Calibri, sans-serif; font-size: 11pt; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">virtual</span><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0); background-color: white;"> seminar</span><span style="font-family: Calibri, Arial, Helvetica, sans-serif, serif, EmojiFont; font-size: 14.6667px; color: black; background-color: white;">
</span><span style="font-family: Calibri, Arial, Helvetica, sans-serif, serif, EmojiFont; font-size: 11pt; color: black; background-color: white;">given by
</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(32, 32, 32); background-color: rgb(255, 255, 255);">Doreen Fraser of
</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">University of Waterloo and Perimeter Institute for Theoretical Physics</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(36, 36, 36); background-color: white;"> on
the Zoom for Government link: </span></div>
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<span style="background-color: rgb(255, 255, 255);"><a href="https://jlab-org.zoomgov.com/j/1611272505?pwd=OTY2YUhVd3ZPTWZWYUM2Rlc0RVRadz09" id="LPlnk417209" class="OWAAutoLink">https://jlab-org.zoomgov.com/j/1611272505?pwd=OTY2YUhVd3ZPTWZWYUM2Rlc0RVRadz09</a></span></div>
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Please see below for the title and abstract. </div>
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<span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; color: black;"><b><u>Theory Seminar</u></b>:<b> </b></span><span style="font-family: Calibri, Arial, Helvetica, sans-serif, serif, EmojiFont; font-size: 14.6667px; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255);">April
15<sup>th</sup></span><span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; color: black;">, 1pm
</span><span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 14.67px; color: rgb(36, 36, 36); background-color: white;">EDT</span><span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; color: black;"> (</span><span style="font-family: Calibri, sans-serif; font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">virtual</span><span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; color: black;">)</span></p>
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<span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; color: rgb(36, 36, 36);"><b><u>Speaker</u></b>:
</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 14.6667px; color: rgb(32, 32, 32); background-color: rgb(255, 255, 255);">Doreen Fraser</span><span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; color: rgb(36, 36, 36);"> (</span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 14.6667px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">University
of Waterloo and Perimeter Institute for Theoretical Physics</span><span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; color: rgb(36, 36, 36);">) </span></p>
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<span style="font-size: 11pt; color: rgb(36, 36, 36);"><b><u><br>
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<span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; color: rgb(36, 36, 36);"><b><u>Title</u></b>:</span><span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; color: black;"><b> </b></span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">Haag’s
theorem and the status of particles in QFTs with interactions</span><span style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 11pt; color: black; background-color: white;"> </span></p>
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<span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; color: rgb(36, 36, 36);"><b><u>Abstract</u></b>:</span><span style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; color: black;"> </span><span style="font-family: Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">Haag’s
theorem was a result from the 1950s that showed that the interaction picture of QFT can only be consistently used to represent free systems. Infrared divergences are a symptom of this underlying problem. I will discuss the implications of Haag’s theorem for
the foundations of QFT. One important consequence for the interpretation of QFT is that particle descriptions are not fundamental.</span><span style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 11pt; color: rgb(32, 32, 32); background-color: rgb(255, 255, 255);"> </span></p>
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<span style="font-size: 11pt; color: rgb(36, 36, 36);">See you on Monday. </span></p>
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<span style="font-size: 11pt; color: rgb(36, 36, 36);">Best regards, </span></p>
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<span style="font-size: 11pt; color: rgb(36, 36, 36);">Caroline, Joe, and Zheng-Yang</span></p>
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