61,661 research outputs found
Spontaneous symmetry breaking in the -symmetric scalar sector
We present a detailed study of the vacua of the -symmetric
three-Higgs-doublet potential, specifying the region of parameters where these
minimisation solutions occur. We work with a CP conserving scalar potential and
analyse the possible real and complex vacua with emphasis on the cases in which
the CP symmetry can be spontaneously broken. Results are presented both in the
reducible-representation framework of Derman, and in the
irreducible-representation framework. Mappings between these are given. Some of
these implementations can in principle accommodate dark matter and for that
purpose it is important to identify the residual symmetries of the potential
after spontaneous symmetry breakdown. We are also concerned with constraints
from vacuum stability.Comment: 37 pages. v2: Minor changes in the references, matches published
version. v3: Table 6 corrected: two additional cases conserve CP. Related
discussion adapted. Version consistent with JHEP Erratu
Spontaneous symmetry breaking in three-Higgs-doublet -symmetric models
The talk summarises work done by the authors consisting of a detailed study
of the possible vacua in models with three Higgs doublets with symmetry
and without explicit CP violation. Different vacua require special regions of
the parameter space which were analysed in our work. We establish the
possibility of spontaneous CP violation in this framework and we also show
which complex vacua conserve CP. In our work we discussed constraints from
vacuum stability. The results presented here are relevant for model building.Comment: 11 pages, no figures. Prepared for the proceedings of DISCRETE2016:
the Fifth Symposium on Prospects in the Physics of Discrete Symmetries, 28
November-3 December 2016, University of Warsaw, Poland, to appear in the
Journal of Physics: Conference Series (JPCS
Free energy determination of phase coexistence in model C60: A comprehensive Monte Carlo study
The free energy of the solid and fluid phases of the Girifalco C60 model are
determined through extensive Monte Carlo simulations. In this model the
molecules interact through a spherical pair potential, characterized by a
narrow and attractive well, adjacent to a harshly repulsive core. We have used
the Widom test particle method and a mapping from an Einstein crystal, in order
to estimate the absolute free energy in the fluid and solid phases,
respectively; we have then determined the free energy along several isotherms,
and the whole phase diagram, by means of standard thermodynamic integrations.
We highlight how the interplay between the liquid-vapor and the liquid-solid
coexistence conditions determines the existence of a narrow liquid pocket in
the phase diagram, whose stability is assessed and confirmed in agreement with
previous studies. In particular, the critical temperature follows closely an
extended corresponding-states rule recently outlined by Noro and Frenkel [J.
Chem. Phys. 113:2941 (2000)].
We discuss the emerging "energetic" properties of the system, which drive the
phase behavior in systems interacting through short-range forces [A. A. Louis,
Phil. Trans. R. Soc. A 359:939 (2001)], in order to explain the discrepancy
between the predictions of several structural indicators and the results of
full free energy calculations, to locate the fluid phase boundaries.
More generally, we aim to provide extended reference data for calculations of
the free energy of the C60 fullerite in the low temperature regime, as for the
determination of the phase diagram of higher order fullerenes and other
fullerene-related materials, whose description is based on the same model
adopted in this work.Comment: RevTeX, 11 pages, 9 figure
Minimal anomaly-free chiral fermion sets and gauge coupling unification
We look for minimal chiral sets of fermions beyond the standard model that
are anomaly free and, simultaneously, vectorlike particles with respect to
colour SU(3) and electromagnetic U(1). We then study whether the addition of
such particles to the standard model particle content allows for the
unification of gauge couplings at a high energy scale, above GeV so as to be safely consistent with proton decay bounds. The
possibility to have unification at the string scale is also considered.
Inspired in grand unified theories, we also search for minimal chiral fermion
sets that belong to SU(5) multiplets. Restricting to representations up to
dimension 50, we show that some of these sets can lead to gauge unification at
the GUT and/or string scales.Comment: 13 pages, 5 figures, 8 tables; Comments and references added, final
version to appear in Phys. Rev.
Effects of Random Biquadratic Couplings in a Spin-1 Spin-Glass Model
A spin-1 model, appropriated to study the competition between bilinear
(J_{ij}S_{i}S_{j}) and biquadratic (K_{ij}S_{i}^{2}S_{j}^{2}) random
interactions, both of them with zero mean, is investigated. The interactions
are infinite-ranged and the replica method is employed. Within the
replica-symmetric assumption, the system presents two phases, namely,
paramagnetic and spin-glass, separated by a continuous transition line. The
stability analysis of the replica-symmetric solution yields, besides the usual
instability associated with the spin-glass ordering, a new phase due to the
random biquadratic couplings between the spins.Comment: 16 pages plus 2 ps figure
Monte Carlo Simulations of Ultrathin Magnetic Dots
In this work we study the thermodynamic properties of ultrathin ferromagnetic
dots using Monte Carlo simulations. We investigate the vortex density as a
function of the temperature and the vortex structure in monolayer dots with
perpendicular anisotropy and long-range dipole interaction. The interplay
between these two terms in the hamiltonian leads to an interesting behavior of
the thermodynamic quantities as well as the vortex density.Comment: 10 figure
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