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This thesis explores two aspects of the renormalization group (RG) in quantum field theory (QFT). In the first part we study the structure of RG flows in general Poincaré-invariant, unitary QFTs, and in particular the irreversibility properties and the rel ...
We present a renormalizable theory of scalars in which the low-energy effective theory contains a pseudo-Goldstone boson with a compact field space of 2 pi F and an approximate discrete shift symmetry Z(Q) with Q >> 1, yet the number of fields in the theor ...
In the antiferromagnetic ground state, below T-N similar or equal to 5.7 K, Ca2CoSi2O7 exhibits strong magnetoelectric coupling. For a symmetry-consistent theoretical description of this multiferroic phase, precise knowledge of its crystal structure is a p ...
BaTiO3 appears in cubic and hexagonal variants, both of which are centrosymmetric. Samples of cubic BaTiO3 are known to exhibit breaking of the centric symmetry locally and globally. It has been proposed that the local symmetry breaking originates in polar ...
In vortex-like spin arrangements, multiple spins can combine into emergent multipole moments. Such multipole moments have broken space-inversion and time-reversal symmetries, and can therefore exhibit linear magnetoelectric (ME) activity. Three types of su ...
Cell migration is a fundamental property of all animal cells which is involved in processes such as embryogenesis, immune response, tissue regeneration and cancer metastasis. Directional migration requires cell polarization which could happen in response t ...
We revisit the SU(6) Heisenberg model on the honeycomb lattice, which has been predicted to be a chiral spin liquid by mean-field theory [G. Szirmai et al., Phys. Rev. A 84, 011611(R) (2011)]. Using exact diagonalizations of finite clusters, infinite proje ...
Topological insulators have attracted abundant attention for a variety of reasons-notably, the possibility for lossless energy transport through edge states "protected" against disorder. Topological effects such as the quantum Hall state can be induced thr ...
In the present paper, we revisit gravitational theories which are invariant under TDiffs-transverse (volume-preserving) diffeomorphisms and global scale transformations. It is known that these theories can be rewritten in an equivalent diffeomorphism-invar ...
Symmetries are omnipresent and play a fundamental role in the description of Nature. Thanks to them, we have at our disposal nontrivial selection rules that dictate how a theory should be constructed. This thesis, which is naturally divided into two parts, ...