High Energy Physics Seminars

January 24, 2018 Wednesday 2:00 PM
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726 Broadway, 940, CCPP Seminar

**High Energy Physics Seminars**
(hep)

726 Broadway, 940, CCPP Seminar

**Thomas Bachlechner**

Columbia

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Tunneling in Semi-Classical Gravity *

In this seminar I will carefully discuss the solution of the following problem in semi-classical quantum gravity. Consider an object of small mass in a locally Schwarzschild-de Sitter spacetime (Hubble parameter H_A). The object is located in an apparatus that forms a bubble of Hubble parameter H_B, separated via a thin domain wall from the original spacetime. Classically, this domain wall will expand to a finite size and eventually re-collapse. Quantum mechanically, the domain wall can tunnel through a forbidden region and expand indefinitely, leaving the object in a de Sitter region of Hubble parameter H_B, while the apparatus remains unaffected during the quantum transition. The Hamiltonian of a gravitational theory vanishes. I will discuss the quasi-local energy and how it relates to the boundary conditions. I evaluate the probability for tunneling to occur, both for H_A larger and smaller than H_B. The probability can increases with increasing Hubble scale within the bubble. I discuss this naive contradiction with entropy arguments, which would suggest that transitions to a higher entropy (smaller Hubble scale) are favored.

January 31, 2018 Wednesday 2:00 PM
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726 Broadway, 940, CCPP Seminar

**High Energy Physics Seminars**
(hep)

726 Broadway, 940, CCPP Seminar

**Marcus Spradlin**

IAS

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TBA *

February 1, 2018 Thursday 12:30 PM
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726 Broadway, 940, CCPP Seminar

**High Energy Physics Seminars**
(hep)

726 Broadway, 940, CCPP Seminar

**Tanguy Pierog**

Karlsruhe Inst. of Technology

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LHC and Cosmic Rays : the Chicken or the Egg ? *

In recent years the interpretation of high energy cosmic ray measurements took another direction. From the astrophysical point of view, it was usually assumed that extra-galactic charged cosmic rays were protons, but mass composition results from the Pierre Auger Observatory, in particular using hadronic interaction models updated with LHC data, point to a mixed composition at energies well above the ankle of the spectrum. Realistic air shower simulation and hadronic interaction models are the key points for a proper interpretation of charged cosmic ray data, and data measured at the LHC are a fundamental ingredient for these models. On the other hand, hadronic models used for cosmic ray analysis have a better predictive power than traditional high energy physics monte-carlo for minimum bias analysis at the LHC. After a first part dedicated to the post-LHC hadronic interaction models and their comparison to LHC data, the latest results from Pierre Auger Observatory will be presented with a focus given on mass composition and constrains on hadronic interactions ... leading to better models to describe LHC data.

February 7, 2018 Wednesday 2:00 PM
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726 Broadway, 940, CCPP Seminar

**High Energy Physics Seminars**
(hep)

726 Broadway, 940, CCPP Seminar

**Surjeet Rajendran**

Berkeley

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TBA *

February 14, 2018 Wednesday 2:00 PM
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726 Broadway, 940, CCPP Seminar

**High Energy Physics Seminars**
(hep)

726 Broadway, 940, CCPP Seminar

**Clay Cordova**

IAS

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TBA *

February 21, 2018 Wednesday 2:00 PM
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726 Broadway, 940, CCPP Seminar

**High Energy Physics Seminars**
(hep)

726 Broadway, 940, CCPP Seminar

**Xi Yin**

Harvard U.

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TBA *

February 28, 2018 Wednesday 2:00 PM
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726 Broadway, 940, CCPP Seminar

**High Energy Physics Seminars**
(hep)

726 Broadway, 940, CCPP Seminar

**Nima Arkani-Hamed**

IAS

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Marble Statues in the Forest Beyond Quantum Mechanics and Spacetime *

I will give an overview of 5 (clearly connected)
appearances of ``positive geometries" in physics: (1) the
amplituhedron and N=4 SYM, (2) the associahedron and general massless
theories in D dimensions, (3) cosmological polytopes, and
work-in-progress on (4) the positive geometry of effective field
theory (a big generalization of ``positive signs" for operators--where
higher dimension operator coefficients are seen to be constrained to
live inside "UV/IR polytopes"), and (5) the positive geometry of
conformal field theory (which underlies the bootstrap).