992 research outputs found
Complex Scalar DM in a B-L Model
In this work, we implement a complex scalar Dark Matter (DM) candidate in a
gauge extension of the Standard Model. The model contains three
right handed neutrinos with different quantum numbers and a rich scalar sector,
with extra doublets and singlets. In principle, these extra scalars can have
VEVs ( and for the extra doublets and singlets,
respectively) belonging to different energy scales. In the context of
, which allows to obtain naturally
light active neutrino masses and mixing compatible with neutrino experiments,
the DM candidate arises by imposing a symmetry on a given complex
singlet, , in order to make it stable. After doing a study of the
scalar potential and the gauge sector, we obtain all the DM dominant processes
concerning the relic abundance and direct detection. Then, for a representative
set of parameters, we found that a complex DM with mass around GeV, for
example, is compatible with the current experimental constraints without
resorting to resonances. However, additional compatible solutions with heavier
masses can be found in vicinities of resonances. Finally, we address the issue
of having a light CP-odd scalar in the model showing that it is safe concerning
the Higgs and the boson invisible decay widths, and also the energy
loss in stars astrophysical constraints.Comment: 20 pages, 3 figure
Vacuum stability conditions of the economical 3-3-1 model from copositivity
By applying copositivity criterion to the scalar potential of the economical
model, we derive necessary and sufficient bounded-from-below conditions
at tree level. Although these are a large number of intricate inequalities for
the dimensionless parameters of the scalar potential, we present general
enlightening relations in this work. Additionally, we use constraints coming
from the minimization of the scalar potential by means of the orbit space
method, the positivity of the squared masses of the extra scalars, the Higgs
boson mass, the gauge boson mass and its mixing angle with the SM
boson in order to further restrict the parameter space of this model.Comment: 22 pages, 7 figures, added text and references. Matches published
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Accidental symmetries and massless quarks in the economical 3-3-1 model
In the framework of a 3-3-1 model with a minimal scalar sector, known as the
economical 3-3-1 model, we study its capabilities of generating realistic quark
masses. After a detailed study of the symmetries of the model, before and after
the spontaneous symmetry breaking, we find a remaining axial symmetry that
prevents some quarks to gain mass at all orders in perturbation theory. Since
this accidental symmetry is anomalous, we also consider briefly the possibility
to generate their masses for non-perturbative effects. However, we find that
non-perturbative effects are not enough to generate the measured masses for
that three massless quarks. Hence, these results imply that the economical
3-3-1 model is not a realistic description of the electroweak interaction and
it has to be modified.Comment: 11 pages, no figure
Axion Like Particles and the Inverse Seesaw Mechanism
Light pseudoscalars known as axion like particles (ALPs) may be behind
physical phenomena like the Universe transparency to ultra-energetic photons,
the soft -ray excess from the Coma cluster, and the 3.5 keV line. We
explore the connection of these particles with the inverse seesaw (ISS)
mechanism for neutrino mass generation. We propose a very restrictive setting
where the scalar field hosting the ALP is also responsible for generating the
ISS mass scales through its vacuum expectation value on gravity induced
nonrenormalizable operators. A discrete gauge symmetry protects the theory from
the appearance of overly strong gravitational effects and discrete anomaly
cancellation imposes strong constraints on the order of the group. The
anomalous U symmetry leading to the ALP is an extended lepton number and
the protective discrete symmetry can be always chosen as a subgroup of a
combination of the lepton number and the baryon number.Comment: 29pp. v4: published version with erratum. Conclusions unchange
Natural PQ symmetry in the 3-3-1 model with a minimal scalar sector
In the framework of a 3-3-1 model with a minimal scalar sector we make a
detailed study concerning the implementation of the PQ symmetry in order to
solve the strong CP problem. For the original version of the model, with only
two scalar triplets, we show that the entire Lagrangian is invariant under a
PQ-like symmetry but no axion is produced since an U(1) subgroup remains
unbroken. Although in this case the strong CP problem can still be solved, the
solution is largely disfavored since three quark states are left massless to
all orders in perturbation theory. The addition of a third scalar triplet
removes the massless quark states but the resulting axion is visible. In order
to become realistic the model must be extended to account for massive quarks
and invisible axion. We show that the addition of a scalar singlet together
with a Z_N discrete gauge symmetry can successfully accomplish these tasks and
protect the axion field against quantum gravitational effects. To make sure
that the protecting discrete gauge symmetry is anomaly free we use a discrete
version of the Green-Schwarz mechanism.Comment: 18 pages, 1 figure, 3 table
String dynamics in cosmological and black hole backgrounds: The null string expansion
We study the classical dynamics of a bosonic string in the --dimensional
flat Friedmann--Robertson--Walker and Schwarzschild backgrounds. We make a
perturbative development in the string coordinates around a {\it null} string
configuration; the background geometry is taken into account exactly. In the
cosmological case we uncouple and solve the first order fluctuations; the
string time evolution with the conformal gauge world-sheet --coordinate
is given by , where
are given by Eqs.\ (3.15), and is the exponent of the conformal factor
in the Friedmann--Robertson--Walker metric, i.e. . The string
proper size, at first order in the fluctuations, grows like the conformal
factor and the string energy--momentum tensor corresponds to that of
a null fluid. For a string in the black hole background, we study the planar
case, but keep the dimensionality of the spacetime generic. In the null
string expansion, the radial, azimuthal, and time coordinates are
and The first terms of the series represent a
{\it generic} approach to the Schwarzschild singularity at . First and
higher order string perturbations contribute with higher powers of . The
integrated string energy-momentum tensor corresponds to that of a null fluid in
dimensions. As the string approaches the singularity its proper
size grows indefinitely like . We end the paper
giving three particular exact string solutions inside the black hole.Comment: 17 pages, REVTEX, no figure
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