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<span data-ogsb="white" style="">Dear all, </span></div>
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</span><span data-ogsc="rgb(36, 36, 36)" data-ogsb="white" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;">Tomorrow, at 1pm<span> </span></span><span data-ogsc="rgb(36, 36, 36)" data-ogsb="white" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 14.67px; line-height: 1.5;">EDT</span><span data-ogsc="rgb(36, 36, 36)" data-ogsb="white" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;">,
we will have a<span> </span></span><span data-ogsc="rgb(36, 36, 36)" data-ogsb="rgb(255, 255, 255)" style="font-family: Calibri, sans-serif; font-size: 11pt; line-height: 1.5;">virtual</span><span data-ogsc="rgb(0, 0, 0)" data-ogsb="white" style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 11pt; line-height: 1.5;"> seminar</span><span data-ogsc="black" data-ogsb="white" style="font-family: Calibri, Arial, Helvetica, sans-serif, serif, EmojiFont; font-size: 14.6667px; line-height: 1.5;"><span> </span></span><span data-ogsc="black" data-ogsb="white" style="font-family: Calibri, Arial, Helvetica, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;">given
by<span> </span></span><span data-ogsc="rgb(32, 32, 32)" data-ogsb="rgb(255, 255, 255)" style="font-family: Calibri, Helvetica, sans-serif; font-size: 11pt; line-height: 1.5;">Doreen Fraser of<span> </span></span><span data-ogsc="rgb(36, 36, 36)" data-ogsb="rgb(255, 255, 255)" style="font-family: Calibri, Helvetica, sans-serif; font-size: 11pt; line-height: 1.5;">University
of Waterloo and Perimeter Institute for Theoretical Physics</span><span data-ogsc="rgb(36, 36, 36)" data-ogsb="white" style="font-family: Calibri, Helvetica, sans-serif; font-size: 11pt; line-height: 1.5;"> on the Zoom for Government link: </span></div>
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<span data-ogsb="rgb(255, 255, 255)" style=""><a href="https://jlab-org.zoomgov.com/j/1611272505?pwd=OTY2YUhVd3ZPTWZWYUM2Rlc0RVRadz09" class="OWAAutoLink" data-linkindex="0" style="" rel="noreferrer noopener">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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<p data-ogsb="white" style="margin: 0px; text-align: left; text-indent: 0px;"><span data-ogsc="black" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;"><b><u>Theory Seminar</u></b>:<b> </b></span><span data-ogsc="rgb(0, 0, 0)" data-ogsb="rgb(255, 255, 255)" style="font-family: Calibri, Arial, Helvetica, sans-serif, serif, EmojiFont; font-size: 14.6667px; line-height: 1.5;">April
15<sup>th</sup></span><span data-ogsc="black" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;">, 1pm<span> </span></span><span data-ogsc="rgb(36, 36, 36)" data-ogsb="white" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 14.67px; line-height: 1.5;">EDT</span><span data-ogsc="black" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;"> (</span><span data-ogsc="rgb(36, 36, 36)" data-ogsb="rgb(255, 255, 255)" style="font-family: Calibri, sans-serif; font-size: 14.6667px; line-height: 1.5;">virtual</span><span data-ogsc="black" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;">)</span></p>
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<span data-ogsc="rgb(36, 36, 36)" style="font-size: 11pt; line-height: 1.5;"><b><u><br>
</u></b></span></p>
<p data-ogsb="white" style="margin: 0px; text-align: left; text-indent: 0px;"><span data-ogsc="rgb(36, 36, 36)" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;"><b><u>Speaker</u></b>:<span> </span></span><span data-ogsc="rgb(32, 32, 32)" data-ogsb="rgb(255, 255, 255)" style="font-family: Calibri, Helvetica, sans-serif; font-size: 14.6667px; line-height: 1.5;">Doreen Fraser</span><span data-ogsc="rgb(36, 36, 36)" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;"> (</span><span data-ogsc="rgb(36, 36, 36)" data-ogsb="rgb(255, 255, 255)" style="font-family: Calibri, Helvetica, sans-serif; font-size: 14.6667px; line-height: 1.5;">University
of Waterloo and Perimeter Institute for Theoretical Physics</span><span data-ogsc="rgb(36, 36, 36)" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;">) </span></p>
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<span data-ogsc="rgb(36, 36, 36)" style="font-size: 11pt; line-height: 1.5;"><b><u><br>
</u></b></span></p>
<p data-ogsb="white" style="margin: 0px; text-align: left; text-indent: 0px;"><span data-ogsc="rgb(36, 36, 36)" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;"><b><u>Title</u></b>:</span><span data-ogsc="black" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;"><b> </b></span><span data-ogsc="rgb(36, 36, 36)" data-ogsb="rgb(255, 255, 255)" style="font-family: Calibri, Helvetica, sans-serif; font-size: 11pt; line-height: 1.5;">Haag’s
theorem and the status of particles in QFTs with interactions</span><span data-ogsc="black" data-ogsb="white" style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;"> </span></p>
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<span data-ogsc="rgb(36, 36, 36)" style=""><b><u><br>
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<p data-ogsb="white" style="margin: 0px; text-align: left; text-indent: 0px;"><span data-ogsc="rgb(36, 36, 36)" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;"><b><u>Abstract</u></b>:</span><span data-ogsc="black" style="font-family: Calibri, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;"> </span><span data-ogsc="rgb(36, 36, 36)" data-ogsb="rgb(255, 255, 255)" style="font-family: Calibri, Helvetica, sans-serif; font-size: 11pt; line-height: 1.5;">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 data-ogsc="rgb(32, 32, 32)" data-ogsb="rgb(255, 255, 255)" style="font-family: Calibri, Helvetica, sans-serif, serif, EmojiFont; font-size: 11pt; line-height: 1.5;"> </span></p>
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<span data-ogsc="rgb(36, 36, 36)" style="font-size: 11pt; line-height: 1.5;">See you tomorrow. </span></p>
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<span data-ogsc="rgb(36, 36, 36)" style="font-size: 11pt; line-height: 1.5;">Best regards, </span></p>
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<span data-ogsc="rgb(36, 36, 36)" style="font-size: 11pt; line-height: 1.5;">Caroline, Joe, and Zheng-Yang</span></p>
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