Astroparticle Physics
Why can't we observe ultra-high-energy cosmic rays sources directly?
Due to the deflection of Galactic and extragalactic magnetic fields as cosmic rays are charged particles
True or False: Charged pions primarily decay to electrons
False: muons are heavier thus allowing more left & right-handed particles for pions to decay into. Parity violation is more prominent for lighter particles
Explain a possible origin of the "knee" of the cosmic ray energy spectrum
change in the acceleration mechanism at the source / shift to heavier composition due to reduced acceleration efficiency of lighter nuclei
Why are understanding neutrino oscillations important for astroparticle physics?
To understand the flavour of the neutrino at the source, we need to understand how they undergo flavour change as they propagate so that we can better interpret neutrino fluxes.
Explain how W/Z bosons generate mass.
Through the Higgs mechanism : spontaneously breaking the symmetry to require local gauge invariance for EM processes which require mass terms when describing the mechanism with a single boson
Write down the Feynman diagram for neutral pion decay (main channel)
u + ubar -> u -> 2 gamma (t-channel + annihilation)
What are the main candidate sources for cosmic rays below the knee?
Supernovae remnants, pulsar wind nebulae, stellar clusters, acceleration processes within the Galactic Center region
Why does asymptotic freedom occur in QCD?
due to anti-screening of gluons that compete with screening of quarks. If the number of flavours is < 16 (which it is), then the anti-screening dominates
How do neutrinos and gamma rays help us detect UHECR sources?
Since neutrinos & gamma rays are produced from charged pion / kaon decays coming from hadronic interactions from sources, and they do not experience any deflections.
How does the GZK effect work?
Energy loss experienced by UHECRs when interacting with CMB photons. Through photo-pion production, where protons interact with photons, causing a Delta-resonance, decaying into pions which causes the UHECR proton to loose energy. The effect limits the maximum distance in which UHECRs can be produced (propagation distance).
What did the g-2 experiment show?
It showed that the anomalous magnetic moment of the muon was deviating from values derived from the Standard Model with 4.2 sigma, describing a physical process that cannot be described with the Standard Model(https://cerncourier.com/a/an-anomalous-moment-for-the-muon/)
Why is the neutrinoless double beta decay be important? Write down its Feynman diagram.
Neutrinoless double beta decay occurs when no neutrinos are produced through a double beta decay. This would mean that an antineutrino must have been emitted and reabsorbed as a neutrino within the nucleus -> indicates that the neutrino is a Majorana particle. Process: q + q -> 2 W- -> nu_e + 2 e-
Write down the transport equation of cosmic ray in the diffusion-advection limit (i.e. no convection & diffusion in momentum space). Writing the approximate relations for dependence for each term is sufficient
df / dt = - v . del(f) + 1/3 del . v p df/dp + del . (kappa del(f)) + 1/p^2 d/dp(p^2 f b(p)) + j(p)
Here: f: cosmic ray distribution (dN/dp dOmega dV), v : velocity of the medium, kappa : diffusion coefficient, b(p): energy losses
Write the Feynman diagram for the main channel for single top quark production
t-channel scattering, q + b -> W+ -> qp + t
Write down the Feynman diagram for Glashow Resonance and describe how it is important for neutrino physics
e + nubar_e -> W- -> q + qbar. The resonance occurs at ~ 6.3 PeV, and is a diagnostic tool for astrophysical neutrinos (2.3 sigma in IceCube)