Parton distribution functions (PDFs) are vitally important for high energy physics calculations. Vast amounts of experimental evidence have shown that scattering processes involving nuclei cannot...Show moreParton distribution functions (PDFs) are vitally important for high energy physics calculations. Vast amounts of experimental evidence have shown that scattering processes involving nuclei cannot be solved using the free-nucleon formalism of perturbative QCD and therefore, a separate empirical determination of the nuclear modification of PDFs is necessary. Because the shape and size of nuclear modification are theoretically unmotivated, the NNPDF collaboration uses a neural network to achieve a model-independent parametrisation. In this thesis, we include new Z boson production data from pPb collisions into the NNPDF framework and examine its impact on the quality of the fit. We will also discuss the phenomenological implications of prompt photon production data in pPb collisions.Show less
In this thesis we study the use of Boltzmann codes for simulating the evolution of linear perturbations. More specifically we compared the matter power spectra at present as calculated by CAMB and...Show moreIn this thesis we study the use of Boltzmann codes for simulating the evolution of linear perturbations. More specifically we compared the matter power spectra at present as calculated by CAMB and CLASS, as these are the most up to date Boltzmann codes. We have looked at their behavior for a universe with a non-cold dark matter component. For the non-cold dark matter component we used sterile neutrinos with few keV mass and a non thermal primordial distribution function. There is a strong disagreement between the two codes, when the non thermal component is big. We expect a suppression of the matter power spectrum on small scales when comparing it to the cold dark matter case. While CAMB fits our expectations, we see a big deviation in the results from CLASS. An attempt at solving this error was made by changing the way the distribution function is sampled in CLASS however, we only found a small improvement and no conclusive source of this strange behavior.Show less
We review the Standard Model of elementary particles and the three observational evidences of its incompleteness: dark matter, neutrino oscillation, and baryon asymmetry of the universe. A...Show moreWe review the Standard Model of elementary particles and the three observational evidences of its incompleteness: dark matter, neutrino oscillation, and baryon asymmetry of the universe. A particular extension of the Standard model, nuMSM with only three new sterile neutrinos can in principle explain all the mentioned phenomena. This work addresses the relevant question how the observational data constraints the parameter space of the model that can be probed by accelerator experiments. Namely, we investigate how the measurements of neutrino oscillation parameters affect the possible outcomes obtained in SHiP experiment. We demonstrate the results of parameter reconstruction for a sterile neutrino with mass M = 1 GeV.Show less
Heavy Neutral Leptons are well-motivated candidates for explaining beyond Standard Model phenomena such as dark matter, baryon asymmetry of the Universe and neutrino oscillations. A variety of...Show moreHeavy Neutral Leptons are well-motivated candidates for explaining beyond Standard Model phenomena such as dark matter, baryon asymmetry of the Universe and neutrino oscillations. A variety of probes, ranging from collider-based to cosmological, explore regions of their parameter space in a complementary way. This work will delve into the possibility that Big Bang Nucleosynthesis has to offer in constraining their lifetime based on cosmological measurements of the Helium-4 abundance. Results are derived for masses up to 100 MeV and a framework is laid for extending the analysis to higher masses.Show less
At the end of 2015 two collaborations ATLAS and CMS reported the diphoton excess at the invariant mass 750 GeV. In this work we consider the extension of the Standard Model where this peak can be...Show moreAt the end of 2015 two collaborations ATLAS and CMS reported the diphoton excess at the invariant mass 750 GeV. In this work we consider the extension of the Standard Model where this peak can be explained. This model involves a heavy scalar particle and a light scalar particle (axion) that come from the Peccei-Quinn symmetry breaking. Using different experimental data we find the allowed parameter space of the model. We study the possibility to search for the light axion of this model at the intensity frontier experiments and show that, unfortunately, SHiP and NA62 experiments will not be sensitive to the model. At the end we show that this model of 750 GeV excess can be falsified at √(s) = 13 TeV LHC run. We make quantitative predictions for new decay channels involving gauge bosons and one photon plus missing energy.Show less
Big Bang Nucleosynthesis theory together with Hubble expansion law, Cosmic Microwave Background and Large-Scale structure formation constitute the basis of experimental confirmations of the...Show moreBig Bang Nucleosynthesis theory together with Hubble expansion law, Cosmic Microwave Background and Large-Scale structure formation constitute the basis of experimental confirmations of the Standard Cosmology. Primordial nucleosynthesis observables are very sensitive to the details of particle physics at the time of formation of the first nuclei. We analyze the influence of the heavy sterile neutrinos on the primordial plasma and abundances of light chemical elements (H, He, Li incl. isotopes) using the numerical simulations of non-equilibrium particle dynamics in the expanding Universe. Next, demanding the computed abundances to be consistent with modern measurements, we can limit the mass-lifetime parameter space of sterile neutrinos. The obtained constraints will complement the experimental constraints from direct accelerator searches, including currently planned experiments. We apply this approach to the Neutrino Minimal Standard Model that aims to explain simultaneously 3 Beyond the Standard Model problems: dark matter, neutrino oscillations and baryon asymmetry of the Universe.Show less
Despite the success of the Standard Model in the last few decades, we know it is not complete. There is strong motivation for assuming the existence of aditional heavy neutral leptons, which can...Show moreDespite the success of the Standard Model in the last few decades, we know it is not complete. There is strong motivation for assuming the existence of aditional heavy neutral leptons, which can account for active neutrino masses and possibly also have cosmological implications. In this work I consider the Standard Model with two neutral lepton singlets (sterile neutrinos) with degenerated masses in the range $20MeV - 2GeV$. The constraints on the active-sterile neutrino mixing angles are evaluated based on recent neutrino oscillations data. Using these constraints the bounds from accelerator experiments are reanalyzed for the case of the considered model. Finally, the results are compared with cosmological constraints coming from Big Bang nucleosynthesis and the $\nu MSM$ resonant leptogenesis.Show less
