theory-seminar May 2013

theory-seminar@nikhef.nl

6 participants
6 discussions

[Theory-seminar] Lectures on perturbative QCD by Prof. Lorenzo Magnea
by Eric Laenen 24 May '13

24 May '13

Dear All, Prof. Lorenzo Magnea of the University of Turin is visiting Nikhef during May and June, in the context of the LHCPhenoNet training network. He will give 8 lectures on infrared aspects of perturbative QCD: 4 next week, and 4 at the end of June. May 28: 14.00-15.45 , H331 May 29: 14.00-15.45, H331 June: TBA June: TBA Title and abstract are "Soft and Collinear Gluons in Perturbative QCD" I will give a general introduction to the problem of infrared and collinear singularities in massless gauge theories, explaining our current understanding and pointing to several applications. Specifically, I will discuss how singularities arise in Feynman diagram calculations, and how they are bypassed to build meaningful physical observables; I will introduce some of the technology needed to prove factorization theorems and to derive Sudakov resummations for physically interesting cross sections; finally, I will describe some recent developments concerning the structure of singularities for general QCD amplitudes to all orders in perturbation theory. Eric

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[Theory-seminar] Special seminar tomorrow (Friday) -- correction
by Daniel Butter 24 May '13

24 May '13

Hello all, In my previous email, I had misstated the affiliation of the speaker. His main affiliation is Chennai Mathematical Institute, Siruseri. The corrected information is below. The time (3 pm) and the place (H320) remain unchanged. Best, Dan Speaker: N.D. Hari Dass Affiliations: Centre for Quantum Information and Quantum Computation, Indian Institute of Science, Bangalore; and Chennai Mathematical Institute, Siruseri Title: Varieties of Quantum Measurements Abstract: The first explicit model for quantum measurements was given by von Neumann, strongly influenced by Dirac, for the type of measurements that have come to be known as Projective measurements. In these, the outcomes are always eigenvalues and the post-measurement state is the corresponding eigenstate. This has led to a widespread ’belief’ that quantum measurements always ’irretrievably disturb’ the state of the system. But a number of very interesting measurement schemes have emerged since the von Neumann model, and I shall present these varieties of quantum measurements and critically assess them. That will include i) the Arthurs-Kelly type simultaneous measurements of canonically conjugate observables, ii) the Protective measurements of Aharonov and Vaidman that directly measure expectation values, iii) the weak measurements that do not change the system appreciably at all, and finally iv) the weak value measurements that enable direct measurement of ’normalized’ matrix elements of observables between chosen states. The last kinds are also due to Aharonov and Vaidman.

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[Theory-seminar] Special seminar tomorrow (Friday)
by Daniel Butter 23 May '13

23 May '13

Hello all, There will be a special seminar tomorrow (Friday 24 May) at 3 pm in H320. The speaker is N.D. Hari Dass from the Indian Institute for Science; he will be talking about "Varieties of Quantum Measurements." See below for details. Best, Dan Speaker: N.D. Hari Dass (Centre for Quantum Information and Quantum Computation, Indian Institute of Science) Title: Varieties of Quantum Measurements Abstract: The first explicit model for quantum measurements was given by von Neumann, strongly influenced by Dirac, for the type of measurements that have come to be known as Projective measurements. In these, the outcomes are always eigenvalues and the post-measurement state is the corresponding eigenstate. This has led to a widespread ’belief’ that quantum measurements always ’irretrievably disturb’ the state of the system. But a number of very interesting measurement schemes have emerged since the von Neumann model, and I shall present these varieties of quantum measurements and critically assess them. That will include i) the Arthurs-Kelly type simultaneous measurements of canonically conjugate observables, ii) the Protective measurements of Aharonov and Vaidman that directly measure expectation values, iii) the weak measurements that do not change the system appreciably at all, and finally iv) the weak value measurements that enable direct measurement of ’normalized’ matrix elements of observables between chosen states. The last kinds are also due to Aharonov and Vaidman.

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[Theory-seminar] Nikhef theory seminar -- Thursday 23 @ 2pm
by Pierre Artoisenet 23 May '13

23 May '13

Dear all, Tomorrow we have a theory seminar at 2pm *in room N328*. The speaker is Chris Wever from Utrecht, who will talk about Soft and Coulomb resummation. See below for details. Regards, Pierre Speaker: Chris Wever Date/place: May 23, 2pm, N328 Speaker: Chris Wever (Utrecht) Title: Soft and Coulomb resummation: squark and gluino production at the LHC abstract We consider the production of strongly interacting, heavy SUSY pairs at the LHC. When the centre of mass energy is close to the production threshold of the pair, the corresponding cross sections receive large higher-loop QCD corrections. These corrections are classified as the so-called soft logarithms and Coulomb singularities and they lead to a break down of the usual perturbative expansion. In this talk I review the origin of these large corrections and explain how they can be resummed by using Effective Field theories. Finally, I will present some resummed results for the pair production cross sections of heavy squarks and gluinos. Based on: arXiv:1202.2260 and 1211.3408.

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[Theory-seminar] special seminar today
by I-Sheng Yang 21 May '13

21 May '13

Hi All, Tomorrow, May 21th, we have a special seminar in room D1.112 from 12:00 – 13:00. Speaker Daan Meerburg Title: In search of hints of reconance in the CMB power spectrum Abstract: I will present a new method for searching for resonance in the primordial power spectrum. These effects are predicted by a wide variety of models and come in two flavors, one where the oscillations are log spaced and one where the oscillations are linearly spaced. The proposed method treats the oscillations as perturbations on top of the scale invariant power spectrum. This decreases some of the computational demand in the search for resonance because it allows us to precompute the transfer functions and derivatives thereof. We show that we expect most of the degeneracy between late time and primordial parameters to reside in the distance to last scattering and the overall amplitude al low frequencies. The former will introduce a additional uncertainty in phase for log spaced oscillations, while for linear spaced oscillations it changes the effective frequency. Errors in the familiar LCDM parameters can be evade through expansion to higher orders. We test our code on simulated Planck-like data, and show we able to recover fiducial input oscillations with an amplitude a few times $\mathcal{O}(10^{-2})$ at the $95\%$ C.L. We vary all LCDM parameters + oscillatory parameters. We apply the code to WMAP 9 year data and confirm the existence of two possible resonant frequencies for log spaced oscillations and a large number of similar improvements for linear spaced oscillations. We then apply our code to the PLANCK data, and recover PLANCK results for log spaced oscillations at the low frequency end. We extend the search to include high frequencies and show that allowing to vary more parameters allows for larger improvements than found by the Planck team. We will discuss our findings in light of performed simulations at similar frequencies.

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[Theory-seminar] Theory seminar tomorrow (note unusual time)
by Kalliopi Petraki 01 May '13

01 May '13

Hello, Damien George will give us a blackboard presentation tomorrow, 2nd May, on his latest work on "Multiple solutions to renormalisation group flows". Time: 3:30pm Room: H331 Best, Kallia

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theory-seminar May 2013