1. 
 Blesneag, Stefan, et al.
(författare)

Matter field Kahler metric in heterotic string theory from localisation
 2018

Ingår i: Journal of High Energy Physics (JHEP).  11266708 . 10298479. ; :4

Tidskriftsartikel (refereegranskat)abstract
 We propose an analytic method to calculate the matter field Kahler metric in heterotic compactifications on smooth CalabiYau threefolds with Abelian internal gauge fields. The matter field Kahler metric determines the normalisations of the N = 1 chiral superfields, which enter the computation of the physical Yukawa couplings. We first derive the general formula for this Kahler metric by a dimensional reduction of the relevant supergravity theory and find that its Tmoduli dependence can be determined in general. It turns out that, due to large internal gauge flux, the remaining integrals localise around certain points on the compactification manifold and can, hence, be calculated approximately without precise knowledge of the Ricciflat CalabiYau metric. In a final step, we show how this local result can be expressed in terms of the global moduli of the CalabiYau manifold. The method is illustrated for the family of CalabiYau hypersurfaces embedded in P1 x P3 and we obtain an explicit result for the matter field Kahler metric in this case.


2. 
 Scott, Pat, 1982
(författare)

Searches for Particle Dark Matter : Dark stars, dark galaxies, dark halos and global supersymmetric fits
 2010

Doktorsavhandling (övrigt vetenskapligt)abstract
 The identity of dark matter is one of the key outstanding problems in both particle and astrophysics. In this thesis, I describe a number of complementary searches for particle dark matter. I discuss how the impact of dark matter on stars can constrain its interaction with nuclei, focussing on main sequence stars close to the Galactic Centre, and on the first stars as seen through the upcoming James Webb Space Telescope. The mass and annihilation crosssection of dark matter particles can be probed with searches for gamma rays produced in astronomical targets. Dwarf galaxies and ultracompact, primordiallyproduced dark matter minihalos turn out to be especially promising in this respect. I illustrate how the results of these searches can be combined with constraints from accelerators and cosmology to produce a single global fit to all available data. Global fits in supersymmetry turn out to be quite technically demanding, even with the simplest predictive models and the addition of complementary data from a bevy of astronomical and terrestrial experiments; I show how genetic algorithms can help in overcoming these challenges.


3. 
 Aaboud, M, et al.
(författare)

Study of the material of the ATLAS inner detector for Run 2 of the LHC
 2017

Ingår i: Journal of Instrumentation.  : IOP Publishing.  17480221. ; 12:12

Tidskriftsartikel (refereegranskat)abstract
 The ATLAS inner detector comprises three different subdetectors: the pixel detector, the silicon strip tracker, and the transitionradiation drifttube tracker. The Insertable BLayer, a new innermost pixel layer, was installed during the shutdown period in 2014, together with modifications to the layout of the cables and support structures of the existing pixel detector. The material in the inner detector is studied with several methods, using a lowluminosity s=13 TeV pp collision sample corresponding to around 2.0 nb1 collected in 2015 with the ATLAS experiment at the LHC. In this paper, the material within the innermost barrel region is studied using reconstructed hadronic interaction and photon conversion vertices. For the forward rapidity region, the material is probed by a measurement of the efficiency with which single tracks reconstructed from pixel detector hits alone can be extended with hits on the track in the strip layers. The results of these studies have been taken into account in an improved description of the material in the ATLAS inner detector simulation, resulting in a reduction in the uncertainties associated with the chargedparticle reconstruction efficiency determined from simulation. © 2017 CERN.


4. 
 Aad, G., et al.
(författare)

Measurement of the parityviolating asymmetry parameter ab and the helicity amplitudes for the decay Lambda(0)(b) > J/psi Lambda(0) with the ATLAS detector
 2014

Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology).  : American Physical Society.  15502368 . 15507998. ; 89:9

Tidskriftsartikel (refereegranskat)abstract
 A measurement of the parityviolating decay asymmetry parameter, ab, and the helicity amplitudes for the decay.Lambda(0)(b) > J/psi(mu(+) mu()) Lambda(0)(p pi()) is reported. The analysis is based on 1400 Lambda(0)(b)and (Lambda) over bar (0)(b) baryons selected in 4.6 fb(1) of protonproton collision data with a centerofmass energy of 7 TeV recorded by the ATLAS experiment at the LHC. By combining the.0 b and. _ 0 b samples under the assumption of CP conservation, the value of ab is measured to be 0.30 +/ 0.16(stat) +/ 0.06(syst). This measurement provides a test of theoretical models based on perturbative QCD or heavyquark effective theory.


5. 
 Aad, G., et al.
(författare)

Search for massive, longlived particles using multitrack displaced vertices or displaced lepton pairs in pp collisions at root s=8 TeV with the ATLAS detector
 2015

Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology).  : American Physical Society.  15502368 . 15507998. ; 92:7

Tidskriftsartikel (refereegranskat)abstract
 Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. This article presents the results of a search for events containing at least one longlived particle that decays at a significant distance from its production point into two leptons or into five or more charged particles. This analysis uses a data sample of protonproton collisions at root s = 8 TeV corresponding to an integrated luminosity of 20.3 fb(1) collected in 2012 by the ATLAS detector operating at the Large Hadron Collider. No events are observed in any of the signal regions, and limits are set on model parameters within supersymmetric scenarios involving Rparity violation, split supersymmetry, and gauge mediation. In some of the search channels, the trigger and search strategy are based only on the decay products of individual longlived particles, irrespective of the rest of the event. In these cases, the provided limits can easily be reinterpreted in different scenarios.


6. 
 Aartsen, M. G., et al.
(författare)

Computational techniques for the analysis of small signals in highstatistics neutrino oscillation experiments
 2020

Ingår i: Nuclear Instruments and Methods in Physics Research Section A.  01689002 . 18729576. ; 977

Tidskriftsartikel (refereegranskat)abstract
 The current and upcoming generation of Very Large Volume Neutrino Telescopes  collecting unprecedented quantities of neutrino events  can be used to explore subtle effects in oscillation physics, such as (but not restricted to) the neutrino mass ordering. The sensitivity of an experiment to these effects can be estimated from Monte Carlo simulations. With the high number of events that will be collected, there is a tradeoff between the computational expense of running such simulations and the inherent statistical uncertainty in the determined values. In such a scenario, it becomes impractical to produce and use adequatelysized sets of simulated events with traditional methods, such as Monte Carlo weighting. In this work we present a staged approach to the generation of expected distributions of observables in order to overcome these challenges. By combining multiple integration and smoothing techniques which address limited statistics from simulation it arrives at reliable analysis results using modest computational resources.


7. 
 Arnadottir, Anna, et al.
(författare)

Universums mörka hemlighet
 2018

Konstnärligt arbete (övrigt vetenskapligt)abstract
 Here we follow the exciting exploration of dark matter, from the Big Bang to its anticipated discovery at the Large Hadron Collider. The first hints of dark matter were wound by Fritz Zwicky, the scientist who coined the term. We get to see the astral choreography witnessed by Vera Rubin in the Andromeda galaxy and then plummet deep underground to see the most sensitive dark matter detector on Earth, housed in a former gold mine.From there, we journey across space and time to the Large Hadron Collider at CERN, speeding alongside particles before they collide in visually stunning explosions of light and sound, while learning how scientists around the world are collaborating to track down the constituents of dark matter.


8. 
 Forsberg, Mats, 1978
(författare)

Gravitational perturbations in plasmas and cosmology
 2010

Doktorsavhandling (övrigt vetenskapligt)abstract
 Gravitational perturbations can be in the form of scalars, vectors or tensors. This thesis focuses on the evolution of scalar perturbations in cosmology, and interactions between tensor perturbations, in the form of gravitational waves, and plasma waves. The gravitational waves studied in this thesis are assumed to have small amplitudes and wavelengths much shorter than the background length scale, allowing for the assumption of a flat background metric. Interactions between gravitational waves and plasmas are described by the EinsteinMaxwellVlasov, or the EinsteinMaxwellfluid equations, depending on the level of detail required. Using such models, linear wave excitation of various waves by gravitational waves in astrophysical plasmas are studied, with a focus on resonance effects. Furthermore, the influence of strong magnetic field quantum electrodynamics, leading to detuning of the gravitational waveelectromagnetic wave resonances, is considered. Various nonlinear phenomena, including parametric excitation and wave steepening are also studied in different astrophysical settings. In cosmology the evolution of gravitational perturbations are of interest in processes such as structure formation and generation of large scale magnetic fields. Here, the growth of density perturbations in KantowskiSachs cosmologies with positive cosmological constant is studied.


9. 
 Hartman, H., et al.
(författare)

The FERRUM project : experimental and theoretical transition rates of forbidden [Sc II] lines and radiative lifetimes of metastable ScII levels
 2008

Ingår i: Astronomy and Astrophysics.  : EDP Sciences.  00046361 . 14320746. ; 480:2, s. 575580

Tidskriftsartikel (refereegranskat)abstract
 Context. In many plasmas, longlived metastable atomic levels are depopulated by collisions (quenched) before they decay radiatively. In lowdensity regions, however, the low collision rate may allow depopulation by electric dipole (E1) forbidden radiative transitions, socalled forbidden lines (mainly M1 and E2 transitions). If the atomic transition data are known, these lines are indicators of physical plasma conditions and used for abundance determination. Aims. Transition rates can be derived by combining relative intensities between the decay channels, socalled branching fractions (BFs), and the radiative lifetime of the common upper level. We use this approach for forbidden [Sc II] lines, along with new calculations. Methods. Neither BFs for forbidden lines, nor lifetimes of metastable levels, are easily measured in a laboratory. Therefore, astrophysical BFs measured in Space Telescope Imaging Spectrograph (STIS) spectra of the strontium filament of Eta Carinae are combined with lifetime measurements using a laser probing technique on a stored ionbeam (CRYRING facility, MSL, Stockholm). These quantities are used to derive the absolute transition rates (Avalues). New theoretical transition rates and lifetimes are calulated using the CIV3 code. Results. We report experimental lifetimes of the Sc II levels 3d(2) a(3)P(0,1,2) with lifetimes 1.28, 1.42, and 1.24 s, respectively, and transition rates for lines from these levels down to 3d4s a(3)D in the region 82708390 angstrom. These are the most important forbidden [Sc II] transitions. New calculations for lines and metastable lifetimes are also presented, and are in good agreement with the experimental data.


10. 
 Hartman, Henrik, et al.
(författare)

The FERRUM project: experimentally determined metastable lifetimes and transition probabilities for forbidden [Ti II] lines observed in eta Carinae
 2005

Ingår i: Monthly Notices of the Royal Astronomical Society.  : Oxford University Press.  13652966 . 00358711. ; 361:1, s. 206210

Tidskriftsartikel (refereegranskat)abstract
 In the spectrum of an emissionline region ejected from the massive star Eta Carinae, called the strontium filament (SrF), forbidden lines from many elements, in particular [Sr II] and [Ti II], are observed. These lines are strong in this specific region and valuable for plasma diagnostics. Forbidden lines are not easily produced in laboratory light sources and the atomic parameters for these lines can thus not be measured in a straightforward way. We use a combination of laboratory and astrophysical measurements to determine transition probabilities for the [Ti II] lines. Lifetimes for metastable levels in Ti II are measured using a laser probing technique on a stored ion beam at CRYRING, MSL, Stockholm. Branching fractions from some of these levels are derived from Hubble Space Telescope/STIS spectra of the SrF. The astrophysical branching fractions are combined with the experimental lifetimes to determine absolute transition probabilities. We report lifetimes for the Ti II levels b(4)P(3/2), b(2)P(1/2), c(2)D(3/2) and c(2)D(5/2), in the range 0.2917 s, and transition probabilities for eight parityforbidden lines from the levels c(2)D(3/2) and c(2)D(5/2), along with uncertainty estimates.

