SnowMass2021

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====== TF06: Theory techniques for precision physics ======
Co-Conveners: Radja Boughezal (ANL), Zoltan Ligeti (LBNL)

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**Short description:** 
Testing our theories as precisely as possible and maximizing the discovery potential for new physics have motivated the development of new calculational techniques with increasing precision.  Working group TF06 will survey the theoretical techniques developed to meet the precision demands of current and planned experiments in both the energy and intensity frontiers. TF06 will also investigate what new theoretical developments may be necessary to meet precision benchmarks set by potential future experiments. Discussion topics include but are not limited to:


  * **Effective field theories of QCD:**  The effective field theory approach was very successful in providing important results in various fields. An example is Soft-Collinear-Effective-Theory (SCET), which bridges the energy and intensity frontiers and has led to novel ways of understanding and calculating with precision collider observables. Possible discussion topics for TF06 in this direction include the development of new event-shape variables such as N-jettiness that have led to significant progress in the fields of jet substructure and precision perturbative calculations in QCD.

  * **Multi-loop techniques:** New mathematical structures appear as we deepen our theoretical understanding of collider observables. Examples include but are not limited to the elliptic integrals that appear at the three-loop order for Higgs boson production as well as many important observables. 

  * **Next-to-next-to-leading order and beyond:** As the precision frontier evolves from NNLO to N3LO, extensions of the current theoretical techniques become critical to achieve results that allow an incisive comparison between predictions and data. Examples include the extension of subtraction schemes to N3LO as well as the calculation of the necessary amplitudes. TF06 will survey progress in this direction.

  * **Theoretical improvements in Monte Carlo event generators:** A realistic description of hadronic final states requires accurate Monte Carlo tools that connect high-scale perturbative physics with low-scale hadronization effects.  TF06 will survey current efforts to improve techniques for perturbative matching and merging, the interplay of resummation accuracy with parton shower algorithms, improved descriptions of non-perturbative effects, and other issues.

  * **Standard Model Effective Field Theory (SMEFT):** The lack of new particle discoveries since the Higgs suggests that there is some energy gap above the SM.  Thus, all experimental data can be interpreted in an effective theory obeying SM gauge symmetries.  TF06 will explore the future sensitivity of this program, including subtle effects such as the possibility of isolating dimension-8 operator contributions at the HL-LHC and future colliders such as the EIC.

  * **Parton Distribution Functions (PDFs):** PDFs are a vital component of the precision program. They are a necessary input to all theory predictions for hadron colliders. TF06 will survey current efforts for PDF determinations and the road to N3LO PDF extractions.  

  * **Non-perturbative effects in high-energy collisions:** The dramatic improvement in experimental precision has made previously negligible effects important even at high energies. For example, non-perturbative effects potentially proportional to ΛQCD/Q in the Z-pT spectrum became relevant as experimental precision reached below 1%.

  * **Flavor physics:** Several unexpected ~ 3 𝜎 tensions with the SM prompted discarding some model-building prejudices.  New theory ideas triggered many new experimental search directions in both low and high energy colliders.  TF06 will explore this interplay between theoretical ideas and experimental searches.

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**Organized Meetings and workshops:**

* **Theory Frontier Kick-off Town Hall meeting, July 30, 2020:** \\
During this meeting we have organized a breakout session with short review talks to encourage LOI submissions - https://indico.fnal.gov/event/44512/

* ** Snowmass Community Planning Meeting (CPM), Oct. 5-9, 2020:** \\
TF06 has  co-orgonized the following three sessions during the CPM meeting:\\

- //EFTs for New Physics Sensitivity//, a joint session between EF04, TF02, TF06 and  RF  -  https://indico.fnal.gov/event/44870/sessions/16313/#20201006  \\
- //From Amplitudes to Precision Theory for Future Colliders//, a joint session between CompF02, EF04, TF04 and TF06 -  https://indico.fnal.gov/event/44870/sessions/16315/#20201006 \\
- //Anomalies in Flavor Physics//, a joint session between RF01, TF05 and TF06 -  https://indico.fnal.gov/event/44870/sessions/16238/#20201007 \\

The //Theory Frontier planning// session during which TF06 presented updates on the group activities can also be found here:\\
 https://indico.fnal.gov/event/44870/sessions/16246/#20201007

* ** Joint meeting between EF05, EF06 and TF06 to discuss a collaborative PDF white paper, Nov. 2, 2020:**\\
https://indico.fnal.gov/event/46116/

* **Workshop on ``Theory meets experiment on |Vub| and |Vcb|", January 11-12, 2021:**\\
This workshop is organized jointly between RF01, TF05 and TF06. The details can be found in the following link: https://indico.fnal.gov/event/46246/


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**Useful information:**\\
- How to join TF06 mailing list:  send an e-mail to listserv@fnal.gov with a blank subject line and the following line in the message body:  SUBSCRIBE SNOWMASS-TF-06-PRECISION FirstName LastName

- Please consider joining our topical group's Slack channel: #tf06-precision 

- Contributed papers and submissions to the Snowmass 2021 proceedings: please follow this link for more details
https://snowmass21.org/submissions/start

Back to the Theory Frontier main page: https://snowmass21.org/theory/

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**Submitted LOIs:**\\
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