Particle theory

Abstract:

The proposed Large Hadron Electron Collider (LHeC) at CERN would bring Deep- Inelastic scattering into the unexplored TeV regime. The LHeC rich physics program, among other topics, includes both precision SM measurements to complement LHC physics as well as studies of QCD in the high energy limit. The present contribution reports on ongoing studies within the NNPDF framework towards the LHeC CDR. We study the impact of LHeC simulated data on PDF uncertainties, in particular the small- x gluon. We also assess the LHeC potential to disentangle between various scenarios of small-x QCD, including saturation models and small-x resummation. Finally, we explore how deviations from DGLAP can be quantified in inclusive measurements.

Abstract:

We give a simple tutorial introduction to the Mathematica package STRINGVACUA, which is designed to find vacua of string-derived or inspired four-dimensional N = 1 supergravities. The package uses powerful algebro-geometric methods, as implemented in the free computer algebra system Singular, but requires no knowledge of the mathematics upon which it is based. A series of easy-to-use Mathematica modules are provided which can be used both in string theory and in more general applications requiring fast polynomial computations. The use of these modules is illustrated throughout with simple examples. Program summary: Program title: STRINGVACUA. Catalogue identifier: AEBZ_v1_0. Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEBZ_v1_0.html. Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland. Licensing provisions: GNU GPL. No. of lines in distributed program, including test data, etc.: 31 050. No. of bytes in distributed program, including test data, etc.: 163 832. Distribution format: tar.gz. Programming language: "Mathematica" syntax. Computer: Home and office spec desktop and laptop machines, networked or stand alone. Operating system: Windows XP (with Cygwin), Linux, Mac OS, running Mathematica V5 or above. RAM: Varies greatly depending on calculation to be performed. Classification: 11.1. External routines: Linux: The program "Singular" is called from Mathematica. Windows: "Singular" is called within the Cygwin environment from Mathematica. Nature of problem: A central problem of string-phenomenology is to find stable vacua in the four-dimensional effective theories which result from compactification. Solution method: We present an algorithmic method, which uses techniques of algebraic geometry, to find all of the vacua of any given string-phenomenological system in a huge class. Running time: Varies greatly depending on calculation requested. © 2008 Elsevier B.V. All rights reserved.

Abstract:

We report on a search with the IceCube detector for high-energy muon neutrinos from GRB080319B, one of the brightest gamma-ray bursts (GRBs) ever observed. The fireball model predicts that a mean of 0.1 events should be detected by IceCube for a bulk Lorentz boost of the jet of 300. In both the direct on-time window of 66s and an extended window of about 300s around the GRB, no excess was found above background. The 90% CL upper limit on the number of track-like events from the GRB is 2.7, corresponding to a muon neutrino fluence limit of 9.5 × 10-3 erg cm-2 in the energy range between 120 TeV and 2.2 PeV, which contains 90% of the expected events. © 2009 The American Astronomical Society. All rights reserved.

Abstract:

We study the spectrum of closed flux tubes in four dimensional SU(N) gauge theories. We do so by calculating the energies of the low lying states with the variational technique (whose basis consists of about 700 operators). We study states of different values of angular momentum, transversal parity, longitudinal parity, and longitudinal momentum, and compare the results with effective string theories (ESTs) such as the Nambu-Goto (NG) model. Most of our states agree very well with the Nambu-Goto predictions and since most of our flux-tubes' lengths are outside the radius of convergence of the ESTs, then for some states it is only the NG that predicts the spectrum well. This strongly suggests that the ESTs can be re-summed. Nonetheless, there are a few states (all with negative parity and in the same representation of the lattice rotation group) that exhibit large deviations from the NG predictions; these deviations might provide clues to the nature of the effective string theory describing the large-N QCD string.