Nikhef Theory Seminar http://www.nikhef.nl/pub/theory/seminar.html Schedule of the theory group seminar at Nikhef en-us Fri, 19 Mar 2010 12:20:48 +0100 php http://cyber.law.harvard.edu/rss/rss.html Nikhef http://www.nikhef.nl/fileadmin/design/resources/logo.jpg http://www.nikhef.nl/pub/theory/seminar.html 100 44 TBA Date: 22-04-10 14:00 (Room H331)
Speaker: Sebastian Klein theory-wide@nikhef.nl (Nikhef Theory) Thu, 22 Apr 2010 14:00:00 +0200 TBA Date: 08-04-10 14:00 (Room H331)
Speaker: Bartomeu Fiol theory-wide@nikhef.nl (Nikhef Theory) Thu, 08 Apr 2010 14:00:00 +0200 First global NNPDF parton analysis. Date: 25-03-10 14:00 (Room H331)
Speaker: Maria Ubiali
Abstract: I present the new global NNPDF2.0 analysis of the content of the proton at next-to-leading order, from a global set of hard scattering data. Experimental data include deep–inelastic scattering, fixed target Drell-Yan production, collider weak boson production and inclusive jet production. I discuss the dataset, its statistical features and its Monte Carlo representation. I present the resulting set of parton distributions, discuss its properties and compare it to other recent parton sets. Finally, I show an improved technique for a fast and accurate solution of the partonic evolution equations and its application to the fast NLO computation of the Drell-Yan observables. theory-wide@nikhef.nl (Nikhef Theory) Thu, 25 Mar 2010 14:00:00 +0100 ZZ+jet and Graviton+jet at NLO QCD: recent applications using GOLEM methods Date: 11-03-10 14:00 (Room H331)
Speaker: Stefan Karg
Abstract:

In my talk I report on the calculation of Z-boson pair + 1 jet production at NLO QCD which is an important background process for Higgs and new physics searches. I will show that the QCD corrections improve the theoretical prediction with respect to scale variations which are used as an estimate of the theory uncertainty. At the LHC however, the appearence of new channels at NLO destabilize the scale behaviour. A significant scale reduction can only be obtained after vetoing the contribution of these channels by applying on the second jet.

Furthermore, this talk also reports on the calculation graviton production in association with a hard jet in large extra dimensions including QCD corrections. The experimental signal, a monojet plus missing energy, has a strong ability to probe the scale of higher extra dimensions. I show how QCD corrections improve the theoretical prediction and discuss other sources of theoretical uncertainties.

 theory-wide@nikhef.nl (Nikhef Theory) Thu, 11 Mar 2010 14:00:00 +0100 A new infrared regularization for planar N=4 super Yang-Mills Date: 25-02-10 14:00 (Room H331)
Speaker: Johannes Henn
Abstract: I present an alternative to dimensional regularization of planar scattering amplitudes in N=4 super Yang-Mills by going to the Coulomb phase of the theory. The infrared divergences are regulated by masses obtained from a Higgs mechanism, allowing us to work in four dimensions. An important feature is that the previously discovered dual conformal symmetry becomes exact thanks to new terms acting on the Higgs masses. I also argue that exponentiation and Regge limits are easier to study compared to dimensional regularization. These ideas are illustrated by explicit results for the four-point amplitude up to three loops. theory-wide@nikhef.nl (Nikhef Theory) Thu, 25 Feb 2010 14:00:00 +0100 Model Building Constraints for type IIB Orientifolds Date: 18-02-10 14:00 (Room H331)
Speaker: Erik Plauschinn
Abstract: In this talk, I discuss constraints for string theory constructions in the context of type IIB orientifold compactifications. In particular, in the first part of my talk I will focus on the tadpole cancellation conditions, the generalised Green-Schwarz mechanism and the computation of Fayet-Iliopoulos terms in the case of an orientifold projection leading to anti-invariant two- and four- cycles. In the second part of my talk, I discuss the general question of implementing an MSSM sector realised by D-branes into moduli stabilisation scenarios. theory-wide@nikhef.nl (Nikhef Theory) Thu, 18 Feb 2010 14:00:00 +0100 Constants of motion deduced from a canonical algorithm Date: 15-02-10 11:00 (Room H320)
Speaker: Jean-Paul Ngome theory-wide@nikhef.nl (Nikhef Theory) Mon, 15 Feb 2010 11:00:00 +0100 Asymptotic expansions of Maximum Likelihood estimators errors, with an application to gravitational waves generated in the inspiral phase of binary mergers Date: 11-02-10 11:00 (Room H331)
Speaker: Salvatore Vitale
Abstract: In this talk we describe a new methodology to calculate analytically the error for a maximum likelihood estimate (MLE) of physical parameters from Gravitational Wave (GW) signals. All the existing literature focuses on the usage of the Cramer Rao Lower bounds (CRLB) as a mean to approximate the errors for large signal to noise ratios. We show here how the variance and the bias of a MLE estimate can be expressed instead in inverse powers of SNRs where the first order in the variance expansion is the CRLB. As an application we compute the second order of the variance and bias for MLE of physical parameters from the inspiral phase of binary mergers and for noises of gravitational wave interferometers. The examples are limited to a single, optimally oriented, interferometer. We also compare the improved error estimate with existing numerical estimates. The value of the second order of the variance expansions allows to get error predictions closer to what is observed in numerical simulations. It also predicts correctly the necessary SNR to approximate the error with the CRLB and provides new insight on the relationship between waveform properties SNR and estimation errors. For example the timing match filtering becomes optimal only if the SNR is larger than the kurtosis of the gravitational wave spectrum. The power expansions can also be used for multiple measurements of the same observable. In that case the SNR should be replaced with SNR times the number of measurements. theory-wide@nikhef.nl (Nikhef Theory) Thu, 11 Feb 2010 11:00:00 +0100 An emergent Fermi Liquid from a strongly coupled quantum critical point Date: 04-02-10 14:00 (Room H331)
Speaker: Koenraad Schalm theory-wide@nikhef.nl (Nikhef Theory) Thu, 04 Feb 2010 14:00:00 +0100 Weak boson scattering at the LHC Date: 28-01-10 14:00 (Room H331)
Speaker: Barbara Jäger theory-wide@nikhef.nl (Nikhef Theory) Thu, 28 Jan 2010 14:00:00 +0100 Quantum Gravity/ADD at the LHC Date: 03-12-09 14:00 (Room H331)
Speaker: Priscila De Aquino theory-wide@nikhef.nl (Nikhef Theory) Thu, 03 Dec 2009 14:00:00 +0100 Are vortices boundaries of singular monopoles? Date: 26-11-09 14:00 (Room H331)
Speaker: João Baptista theory-wide@nikhef.nl (Nikhef Theory) Thu, 26 Nov 2009 14:00:00 +0100 Modelling an extra dimension with domain-wall branes Date: 05-11-09 14:00 (Room H331)
Speaker: Damien George
Abstract: Extensions to the standard model of particle physics are vast and numerous. Particular attention has been given to models incorporating large extra dimensions, building on the idea of the Randall-Sundrum warped metric. I will focus on a variant of the second Randall-Sundrum model, where the extra dimension is infinite in size and the so called "brane" is generated by a bulk scalar field. This model is motivated by the desire to have the action symmetric in all spatial dimensions, with three-dimensionality arising from the spontaneous formation of a domain-wall. I will show how such a domain-wall forms, how scalar fields and massless chiral fermions can be confined to the domain-wall region, and how gauge fields can be incorporated using the Dvali-Shifman mechanism. I will use these building blocks to write down an SU(5) grand unified standard model in 4+1-dimensions. I will then outline the modifications to cosmology, in particular the expansion rate of the universe, that such a theory implies. theory-wide@nikhef.nl (Nikhef Theory) Thu, 05 Nov 2009 14:00:00 +0100 Discrete flavour symmetries in neutrino oscillations, LFV and leptogenesis Date: 01-10-09 14:00 (Room H331)
Speaker: Luca Merlo theory-wide@nikhef.nl (Nikhef Theory) Thu, 01 Oct 2009 14:00:00 +0200 TBA Date: 24-09-09 11:00 (Room H331)
Speaker: Jochum van der Bij theory-wide@nikhef.nl (Nikhef Theory) Thu, 24 Sep 2009 11:00:00 +0200 Model-independent approaches to missing energy signals at the LHC Date: 31-08-09 14:00 (Room H331)
Speaker: Johan Alwall
Abstract: Signatures involving missing energy are among the most enticing at the LHC, since they might indicate the production of Dark Matter. Such signals have most commonly been approached in the framework of the minimal supersymmetric extension of the Standard Model. This model is however only one in a class of models involving a new conserved quantum number, which ensures stability of a Dark Matter particle. I will here present model-independent approaches to this type of signals, which avoid restricting the analysis of these signals to SUSY, and instead allows for comparisons with, and interpretations in terms of, any model. theory-wide@nikhef.nl (Nikhef Theory) Mon, 31 Aug 2009 14:00:00 +0200 Bulk Fermions in Soft Wall Models Date: 20-08-09 14:00 (Room H331)
Speaker: Mert Aybat
Abstract: Models with warped extra dimensions and a soft infrared wall provide an exciting realization of electroweak symmetry breaking, with phenomenological implications that go beyond the standard Randall-Sundrum model with a hard wall. We incorporate bulk fermions in soft wall models and study electroweak and flavor constraints in fully realistic models, including a heavy top quark. We also discuss LHC phenomenology for these models. theory-wide@nikhef.nl (Nikhef Theory) Thu, 20 Aug 2009 14:00:00 +0200 Quantum Extremism: The Convexity Problem in Minkowski Space Date: 09-07-09 14:00 (Room N328)
Speaker: Marcel van Kessel
Abstract: The reality and convexity of the effective potential in quantum field theories has been studied extensively in the context of Euclidean space-time. It has been shown that canonical and path-integral approaches may yield different results, thus resolving the \'convexity problem\'. We discuss the transferral of these treatments to Minkowskian space-time, which also necessitates a careful discussion of precisely which field configurations give the dominant contributions to the path integral. In particular, we study the effective potential for the N=1 linear sigma model. theory-wide@nikhef.nl (Nikhef Theory) Thu, 09 Jul 2009 14:00:00 +0200 Supersymmetric 3-3-1 model and inflationary scenarios Date: 02-07-09 14:00 (Room H331)
Speaker: Hoang Ngoc Long theory-wide@nikhef.nl (Nikhef Theory) Thu, 02 Jul 2009 14:00:00 +0200 Towards the Standard Model on Fractional Branes Date: 04-06-09 14:00 (Room H331)
Speaker: Gabriele Honecker
Abstract: If string theory is the one unifying theory for gauge theories and gravity, it should be able to reproduce the known features of particle physics. One attempt to realise the Standard Model from string theory compactifications consists of intersecting D6-branes in type IIA orientifolds. I will briefly review the characertistic features and compare them with other string constructions. I will then proceed to a recently found phenomenologically appealing class of supersymmetric Standard Model spectra on the Z6\' orbifold and present the computation of gauge thresholds for the fractional branes employed. theory-wide@nikhef.nl (Nikhef Theory) Thu, 04 Jun 2009 14:00:00 +0200 Towards Jetography Date: 09-04-09 14:00 (Room H331)
Speaker: Gavin Salam
Abstract: This talk will start with an overview of past years\' work to put LHC jet finding on a reliable footing, and in particular satisfying the Snowmass requirements, which were set out nearly 20 years ago. It will then proceed to examine how jet-finding might evolve in coming years. In particular I will discuss ongoing work that uses QCD calculations to guide jet-finding choices, with a long term goal of developing a form of autofocus for jets, so as to provide easy and optimal \'jetography\' even for non-experts. theory-wide@nikhef.nl (Nikhef Theory) Thu, 09 Apr 2009 14:00:00 +0200 Moduli Stabilisation and Orientifold Reductions Date: 02-04-09 14:00 (Room N328)
Speaker: Diederik Roest
Abstract: An important issue in string theory is the stabilisation of moduli. After an introduction to the subject, we will discuss recent results on how this can be achieved in a simple setting by orientifold reductions with fluxes. theory-wide@nikhef.nl (Nikhef Theory) Thu, 02 Apr 2009 14:00:00 +0200 QCD radiation in the production of heavy colored particles at the LHC Date: 26-03-09 14:00 (Room F013)
Speaker: Simon de Visscher theory-wide@nikhef.nl (Nikhef Theory) Thu, 26 Mar 2009 14:00:00 +0100 Towards heterotic MSSM orbifolds in blowup Date: 20-02-09 13:00 (Room H331)
Speaker: Stefan Groot Nibbelink
Abstract: Heterotic orbifolds provide promising constructions of MSSM-like models in string theory. We investigate the connection of such orbifold models with smooth Calabi-Yau compactifications by examining resolutions of the T^6/Z6--II orbifold (which are far from unique) with Abelian gauge fluxes. These gauge backgrounds are topologically characterized by weight vectors of twisted states; one per fixed point or fixed line. The VEV\'s of these states generate the blowup from the orbifold perspective, and they reappear as axions on the blowup. We explain methods to solve the 24 resolution dependent Bianchi identities and present an explicit solution. Despite that a solution may contain the MSSM particle spectrum, the hypercharge turns out to be anomalous: Since all heterotic MSSM orbifolds analyzed so far have fixed points where only SM charged states appear, its gauge group can only be preserved provided that those singularities are not blown up. theory-wide@nikhef.nl (Nikhef Theory) Fri, 20 Feb 2009 13:00:00 +0100 Gauge Unification in Local String Models: is M_GUT a mirage? Date: 12-02-09 16:00 (Room H331)
Speaker: Joe Conlon
Abstract: I study threshold corrections for local string models. The presence of a large bulk volume gives a significant anomalous contribution when transforming from holomorphic to physical gauge couplings. These suggest the unification scale should be raised from M_s to R M_s. I study these effects in string models and find full agreement for local D3/D3 models. For D3/D7 models I discuss discrepancies with the field theory formula. I comment on implications for gauge coupling unification and the GUT scale. This talk is based on 0901.4350. theory-wide@nikhef.nl (Nikhef Theory) Thu, 12 Feb 2009 16:00:00 +0100 Infinite-dimensional symmetries, integrable systems, and AdS/CFT Date: 29-01-09 14:00 (Room H331)
Speaker: Alessandro Torrielli
Abstract: We will discuss infinite-dimensional (Hopf algebra) symmetries in integrable systems, with special emphasis on the R-matrix formalism, standard mathematical classifications and the role of Yangians. We will then discuss how all this has recently become a powerful tool of investigation in the context of the AdS/CFT conjecture. theory-wide@nikhef.nl (Nikhef Theory) Thu, 29 Jan 2009 14:00:00 +0100 The Free-Fermionic Landscape Date: 04-12-08 14:00 (Room H331)
Speaker: Michael Lennek theory-wide@nikhef.nl (Nikhef Theory) Thu, 04 Dec 2008 14:00:00 +0100