theory-seminar

theory-seminar@nikhef.nl

17 discussions

[Theory-seminar] Theory seminar on Thursday
by Kalliopi Petraki 04 Jun '13

04 Jun '13

Dear all, This is a reminder for the theory seminar this week. Please find the details below. Cheers, Kallia Date/place: Thursday 6 June, 2pm, H331 Speaker: Chris Kouvaris (CP3 Origins, Odense) Title: The Dark Side of Stars Abstract: Observations of compact stars such as white dwarfs and neutrons stars can impose severe constraints on the nature of dark matter. Depending on the dark matter candidate, there are two general types of constraints. The first one is related to dark matter annihilating inside compact stars producing heat that can potentially change the thermal evolution of the star. The second type is related to the so-called asymmetric dark matter scenario. WIMP accretion inside compact stars can lead under certain conditions to the formation of a mini black hole that can eventually destroy the star. The observation of old nearby neutron stars can exclude a class of dark matter models.

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[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] Seminar Wouter Waalewijn, Wed. April 24, 2013 - 15:00, A1.04
by Eric Laenen 23 Apr '13

23 Apr '13

Dear All,**** ** ** Please find details of tomorrow’s seminar by Wouter Waalewijn, which will take place 15:00 in room A1.04 at the UvA. You are all invited to attend.** ** ** ** *Speaker: *Wouter Waalewijn**** *Date & Time:* 24.04.2013, 15:00**** *Location:* A1.04**** *Title:* Precision Calculations for the LHC using N-Jettiness**** *Abstract: * Many interesting collisions at the Large Hadron Collider involve jets, which are important for the analysis of both signal and background events. I will discuss how the N-jettiness observable allows you to calculate these cross sections with high precision. This will be illustrated by two examples: ** 1) Higgs production with a veto on jets, which is important for the determination of the Higgs couplings. 2) The invariant mass of jets, which is a benchmark observable for the structure of jets. By defining observables using charged particle tracks in the detector these methods remain useful as the number of collisions per bunch crossing at the LHC increases. I will briefly comment on a framework I have developed to calculate such observables.**** **

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[Theory-seminar] Seminar at 2 pm today
by Pierre Artoisenet 18 Apr '13

18 Apr '13

Dear all, We have a theory seminar at 2pm today. Please note the location: N328 Cheers, Pierre Date/place: Thursday 18, 2pm, N328 Speaker: Christophe Ringeval (Louvain) Title: Early universe cosmology after Planck 2013 Abstract: The 2013 release of the Planck satellite data has provided unprecedented measurements of the Cosmic Microwave Background anisotropies and much more. Together with a few new observables at our disposal, these results can now be used to improve our understanding of the early universe. After an introduction to CMB physics and a selected summary of the Planck 2013 results, we will illustrate over two examples, cosmic strings and inflation, how the Planck data give us a window to very high energy physics provided one uses enough precise and systematic theoretical predictions.

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[Theory-seminar] Presentation Today (17.04.2013) @ 15:00 - Brock Tweedie (A1.10)
by Wells, Natalie 17 Apr '13

17 Apr '13

Dear All, There will be an extra colloquium today at 15:00, by Brock Tweedie - you are all invited to attend: Date & Time: Wednesday 17th April 2013, 15:00 - 16:00 Location: A1.10 Title: Cornering Light Stops at the Large Hadron Collider Abstract: The recent discovery of the Higgs boson has firmly resolved a deep theoretical mystery, but it has brought another one into sharper focus: What stabilizes the Higgs field's potential against runaway quantum corrections? One of our best answers to this question, supersymmetry, has come under great tension as generic limits from the LHC suggest that superparticles lie well above a TeV. This tension has motivated dedicated searches for those superparticles that are most directly responsible for stabilizing the Higgs, namely stops, the supersymmetric partners of the top quark. Nonetheless, stop searches have notable blind spots even at fairly low masses, such as "compressed" spectra where the stop's decay generates very little missing energy, and "off-shell" regions of parameter space where the energy of the decay is too small to produce a physical top quark. It is therefore possible that the LHC is copiously producing these important particles, but that they remain well-hidden in the current dataset. To help make compressed and off-shell stops more visible, I will introduce a simple strategy capitalizing on the kinematic variable mT2 in the dileptonic decay channel. I will also discuss the effects of top quark spin and the lightest supersymmetric particle's identity, and touch upon other difficult decay modes that are under study. Many thanks, Natalie Natalie Wells Secretariat Institute of Physics (Tues, Wed, Thurs, Fri) Secretariat Astronomical Institute 'Anton Pannnekoek' (Mon) Universiteit van Amsterdam Institute of Physics (IoP), FNWI Postbus 94485 | 1090 GL Amsterdam Science Park 904 | 1090 GL Amsterdam T +31 (0)20 525 7315 | F+31 20 525 5778 Aanwezig op ma | di | wo | do| vr

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