Renormalization of the Abelian-Higgs Model in the R-xi and Unitary gauges and the physicality of its scalar potential

We perform an old school, one-loop renormalization of the Abelian-Higgs model in the Unitary and $R_\xi$ gauges, focused on the scalar potential and the gauge boson mass. Our goal is to demonstrate in this simple context the validity of the Unitary gauge at the quantum level, which could open the way for an until now (mostly) avoided framework for loop computations. We indeed find that the Unitary gauge is consistent and equivalent to the $R_\xi$ gauge at the level of $\beta$-functions. Then we compare the renormalized, finite, one-loop Higgs potential in the two gauges and we again find equivalence. This equivalence needs not only a complete cancellation of the gauge fixing parameter $\xi$ from the $R_\xi$ gauge potential but also requires its $\xi$-independent part to be equal to the Unitary gauge result. We follow the quantum behaviour of the system by plotting Renormalization Group trajectories and Lines of Constant Physics, with the former the well known curves and with the latter, determined by the finite parts of the counter-terms, particularly well suited for a comparison with non-perturbative studies.Comment: 111 pages, 16 figures. In the previous version a factor of 2, regarding the irreducible triangle diagram with only Higgs fields inside the loop, was missed. In this version the missing factor is corrected and due to that, some of the plots have been updated. Minor typos correcte

Καμπύλες σταθερής φυσικής στο Αβελιανό-Χιγγς Μοντέλο

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Φυσική και Τεχνολογικές Εφαρμογές

Thermal effects in Ising Cosmology

We consider a real scalar field in de Sitter background and compute its thermal propagators. We propose that in a dS/CFT context, non-trivial thermal effects as seen by an 'out' observer can be encoded in the anomalous dimensions of the $d = 3$ Ising model. One of these anomalous dimensions, the critical exponent $\eta$, fixes completely a number of cosmological observables, which we computeComment: 15 pages, 2 figures, version accepted for publication, clarifications regarding the thermal propagator added, general presentation improved, references added, typos correcte

Ising Cosmology

Using arguments from holography we propose that the deviation of the cosmological spectral index $n_S$ of scalar fluctuations from unity may be controlled almost entirely by the critical exponent $\eta$ of the $d = 3$ Ising modelComment: 6 pages, 0 figure

Gravitational production of sterile neutrinos

We consider gravitational production of singlet fermions such as sterile neutrinos during and after inflation. The production efficiency due to classical gravity is suppressed by the fermion mass. Quantum gravitational effects, on the other hand, are expected to break conformal invariance of the fermion sector by the Planck scale-suppressed operators irrespective of the mass. We find that such operators are very efficient in fermion production immediately after inflation, generating a significant background of stable or long-lived feebly interacting particles. This applies, in particular, to sterile neutrinos which can constitute cold non-thermal dark matter for a wide range of masses, including the keV scale.Comment: 18 pages, 1 figur

Flavour and Higgs physics in Z2Z_2-symmetric 2HD models near the decoupling limit

With no evidence of any exotic particle detected so far beyond the Standard Model, the new physics may lie above the presently accessible energies at colliders and, at low-energies, can be accounted for via an effective description. The interplay of flavour and Higgs physics data allows setting stringent bounds on the parameters of the effective Lagrangian. In this paper, we focus on $Z_2$-symmetric two Higgs doublet models near the decoupling limit: the corresponding effective description relies on only a few parameters, thus predicting many interesting correlations between observables that work as tests of the theory. We present the results of a global fit to the existing data, updating and extending over the past literature. We comment on the triple Higgs coupling as a probe of an extended scalar sector and on the recent CDF II measurement of the $W$-mass.Comment: 30 pages, 16 figure