Browsing by Subject "particle physics"

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  • Veteli, Peitsa (Helsingin yliopisto, 2020)
    Opetus- ja tutkimusmaailmojen välillä koetaan olevan rako, jota voidaan pitää osasyynä yleisesti havaittuun opiskelijoiden matalaan motivaatioon luonnontieteellisiä aloja kohtaan. Samassa yhteydessä esiin nousevat autenttisuuden ja relevanssin käsitteet, joilla voidaan kuvata eri tavoilla tapahtuvan toiminnan ”aitoutta” tai mielekkyyttä. Tässä työssä esitellään Fysiikan tutkimuslaitos HIP:in (Helsinki Institute of Physics) Avoin data opetuksessa -projektin myötä kehitettyjä merkityksellisen ohjelmoinnin työkaluja, joissa hyödynnetään muun muassa CERNissä toimivan CMS-kokeen (Compact Muon Solenoid) avoimia hiukkastutkimuksen aineistoja. Näiden materiaalien siirtymistä opettajakunnan avuksi tuetaan koulutuksilla, joista kerättyä palautetta analysoidaan tässä tutkielmassa laajemman tiedeopetuksen autenttisuuteen ja avoimen datan hyödyntämiseen liittyvän keskustelun yhteydessä. Avoimen datan hyödyntäminen ja opetuksellinen tutkiminen ovat hyvin nuoria aloja, joiden eturintamaan tämäkin työ asettuu. Aineistoa on kerätty sekä suomalaisilta (n = 64) että kansainvälisiltä (n = 12) toisen asteen opettajilta, minkä lisäksi vertailukohtana käytetään opiskelijatyöpajoista nousseita kommentteja (n = 62). Menetelmänä toimii temaattinen analyysi, jonka tulokset ovat vertailukelpoisia muuhun luonnontieteen opetuksen tutkimuskirjallisuuteen. Tutkimuskysymyksenä on: Miten autenttisuus esiintyy opettajien palautteessa hiukkasfysiikan avoimen datan opetuskäytön kursseilta ja kuinka se vertautuu tiedeopetuksen tutkimuskirjallisuuteen? Tuloksista havaitaan opettajien näkemysten asettuvan hyvin saman suuntaisesti kuin verrokkikirjallisuuden pohjalta olisi voinut olettaakin, yleisimpien autenttisuuden yhteyksien painottuessa tutkijoiden toimintaan verrattaviin työskentelytapoihin ja ”oikean maailman” haasteisiin. Palautteen lähes yksimielinen positiivisuus antaa vahvaa indikaatiota projektin tarjoamien mahdollisuuksien hyödyllisyydestä ja tukee alalla kaivattavien jatkotutkimusten kannattavuutta.
  • Ema, Yohei; Karciauskas, Mindaugas; Lebedev, Oleg; Zatta, Marco (2017)
    Apparent metastability of the electroweak vacuum poses a number of cosmological questions. These concern evolution of the Higgs field to the current vacuum, and its stability during and after inflation. Higgs-inflaton and non-minimal Higgs-gravity interactions can make a crucial impact on these considerations potentially solving the problems. In this work, we allow for these couplings to be present simultaneously and study their interplay. We find that different combinations of the Higgs-inflaton and non-minimal Higgs-gravity couplings induce effective Higgs mass during and after inflation. This crucially affects the Higgs stability considerations during preheating. In particular, a wide range of the couplings leading to stable solutions becomes allowed.
  • Enckell, Vera-Maria; Enqvist, Kari; Räsänen, Syksy; Wahlman, Lumi-Pyry (2020)
    We consider Higgs inflation with an α R2 term. It adds a new scalar degree of freedom, which leads to a two-field model of inflation. We do a complete slow-roll analysis of the three-dimensional parameter space of the R2 coefficient α, the non-minimal coupling ξ and the Higgs self-coupling λ. We find three classes of inflationary solutions, but only pure R2 and attractor solutions fit observations. We find that pure Higgs inflation is impossible when the R2 term is present regardless of how small α is. However, we can have Higgs-like inflation, where the amplitude of the perturbations does not depend on α and the predictions as a function of e-folds are the same as in Higgs inflation, although the inflationary trajectory is curved in field space. The spectral index is 0.939 < nR < 0.967, and constraining it to the observed range, the tensor-to-scalar ratio varies from 3.8×10−3 to the maximum allowed by observations, 0.079. Observational constraints on isocurvature perturbations contribute to these limits, whereas non-Gaussianity is automatically in the range allowed by observations.
  • Kärkkäinen, Timo (Helsingfors universitet, 2013)
    Neutrino oscillation is a particle physics phenomenon, where neutrino flavour is not conserved. The phenomenon was conjectured during the 1950s by Pontecorvo and confirmed during the 1990s by Super-Kamiokande collaboration. Consequently, neutrinos must have Dirac or Majorana mass and a relevant mass term must be included in standard model. Neutrino oscillation is the first confirmed beyond standard model phenomenon. It leads to nonconservation of quantum numbers L_e, L_μ and L_τ. Currently the scientific community has detected three different neutrinos, but has failed in designating the mass hierarchy and absolute mass of them. In addition, charge-parity symmetry violation (CP violation) is expected, but yet unconfirmed in the neutrino oscillation. This thesis includes a brief historical journey to neutrino physics and a lengthy discussion of electroweak sector of standard model (Glashow–Weinberg–Salam theory), with detailed phenomenology of neutrino oscillations. GLoBES simulation program and its partner AEDL language is introduced. Experiment definition methods in AEDL are covered extensively. The most important parameters are neutrino flux, source power, target mass and baseline length. Statistical methods are represented briefly. Main tool is χ2-test. Neutrino sources are assumed to be 700 kW SPS at CERN, Switzerland, 450 kW particle accelerator Protvino, Russia and 5 MW particle accelerator at Lund, Sweden. The target is LAGUNA detector at Pyhäsalmi mine, Finland. Using specifications of LAGUNA detector currently on drawing board and SPS as the neutrino source, the confidence limits for determining neutrino mass hierarchy and discovering nonzero CP violation are calculated. Mass hierarchy is almost conclusively determined, most of the δ_CP parameter space exceed the 5σ limit, which is considered the limit for a confirmed scientific discovery. CP violation discovery is confirmed within 5σ limit with 70 % of δ_CP parameter space. Including both the SPS and Protvino accelerator neutrino fluxes, the covered parameter space is increased significantly with both mass hierarchy determination and CP violation discovery. Including also Lund accelerator neutrino flux, mass hierarchy is conclusively determined. CP violation discovery is confirmed within 5σ limit with 65 % of δ_CP parameter space and within 90 % limit with 85 % of δ_CP parameter space. Pyhäsalmi mine is 2288 km from CERN neutrino source. The baseline is very close to bimagic baseline 2540 km, which allows extremely good statistics and sensitivity of oscillation parameters. In conclusion, Pyhäsalmi mine should be given priority, when candidate sites are considered.
  • Räsänen, Syksy; Tomberg, Eemeli (2019)
    We study the production of primordial black hole (PBH) dark matter in the case when the Standard Model Higgs coupled non-minimally to gravity is the inflaton. PBHs can be produced if the Higgs potential has a near-critical point due to quantum corrections. In this case the slow-roll approximation may be broken, so we calculate the power spectrum numerically. We consider both the metric and the Palatini formulation of general relativity. Combining observational constraints on PBHs and on the CMB spectrum we find that PBHs can constitute all of the dark matter only if they evaporate early and leave behind Planck mass relics. This requires the potential to have a shallow local minimum, not just a critical point. The initial PBH mass is then below 10(6) g, and predictions for the CMB observables are the same as in tree-level Higgs inflation, n(s) = 0.96 and r = 5 x 10(-3) (metric) or r = 4 x 10(-8) ... 2 x 10(-7) (Palatini).