1,797 research outputs found
Natural Gauge and Gravitational Coupling Unification and the Superpartner Masses
The possibility to achieve unification at the string scale in the context of
the simplest supersymmetric grand unified theory is investigated. We find
conservative upper bounds on the superpartner masses consistent with the
unification of gauge and gravitational couplings, M_{\tilde G} < 5 TeV and
M_{\tilde f} < 3 \times 10^7 GeV, for the superparticles with spin one-half and
zero, respectively. These bounds hint towards the possibility that this
supersymmetric scenario could be tested at future colliders, and in particular,
at the forthcoming LHC.Comment: 8 pages, 4 figures, version accepted in Physics Letters
Anomaly-free U(1) gauge symmetries in neutrino seesaw flavor models
Adding right-handed neutrino singlets and/or fermion triplets to the particle
content of the Standard Model allows for the implementation of the seesaw
mechanism to give mass to neutrinos and, simultaneously, for the construction
of anomaly-free gauge group extensions of the theory. We consider Abelian
extensions based on an extra U(1)_X gauge symmetry, where X is an arbitrary
linear combination of the baryon number B and the individual lepton numbers
L_{e,mu,tau}. By requiring cancellation of gauge anomalies, we perform a
detailed analysis in order to identify the charge assignments under the new
gauge symmetry that lead to neutrino phenomenology compatible with current
experiments. In particular, we study how the new symmetry can constrain the
flavor structure of the Majorana neutrino mass matrix, leading to two-zero
textures with a minimal extra fermion and scalar content. The possibility of
distinguishing different gauge symmetries and seesaw realizations at colliders
is also briefly discussed.Comment: 12 pages, 2 figures, 7 tables; comments and references added, a new
subsection with nonstandard interactions of neutrinos included; final version
to appear in Phys. Rev.
Neutrinos and the Matter-Antimatters Asymmetry in the Universe
The discovery of neutrino oscillations provides a solid evidence for nonzero neutrino masses and leptonic mixing. The fact that neutrino masses are so tiny constitutes a puzzling problem in particle physics. From the theoretical viewpoint, the smallness of neutrino masses can be elegantly explained through the seesaw mechanism. Another challenging issue for particle physics and cosmology is the explanation of the matter-antimatter asymmetry observed in Nature. Among the viable mechanisms, leptogenesis is a simple and well-motivated framework. In this paper we briefly review these aspects, making emphasis on the possibility of linking neutrino physics to the cosmological bary asymmetry originated from leptogenesis
SU(5)xSU(5) unification revisited
The idea of grand unification in a minimal supersymmetric SU(5)xSU(5)
framework is revisited. It is shown that the unification of gauge couplings
into a unique coupling constant can be achieved at a high-energy scale
compatible with proton decay constraints. This requires the addition of a
minimal particle content at intermediate energy scales. In particular, the
introduction of the SU(2)_L triplets belonging to the (15,1)+(\bar{15},1)
representations, as well as of the scalar triplet \Sigma_3 and octet \Sigma_8
in the (24,1) representation, turns out to be crucial for unification. The
masses of these intermediate particles can vary over a wide range, and even lie
in the TeV region. In contrast, the exotic vector-like fermions must be heavy
enough and have masses above 10^10 GeV. We also show that, if the SU(5)xSU(5)
theory is embedded into a heterotic string scenario, it is not possible to
achieve gauge coupling unification with gravity at the perturbative string
scale.Comment: 17 pages, 6 figure
Compact Stars and Magnetized CFL Matter
The stability of the color flavor locked phase in the presence of a strong magnetic field is investigated within the phenomenological MIT bag model. It is found that the minimum value of the energy per baryon in a color flavor locked state at vanishing pressure is lower than the corresponding one for unpaired magnetized strange quark matter and, as the magnetic field increases, the energy per baryon decreases. This implies that magnetized color flavor locked matter is more stable and could become the ground state inside neutron stars. The anisotropy of the pressures is discussed. The mass-radius relation for such stars is also studied
Strange matter in the universe
The strange quark matter hypothesis is one of the most exciting speculations of the XX Century Physics. If this hypothesis is correct, the ground state of the matter would be the strange matter, which could form the core of compact objects like neutron stars or even more exotic objects like quarks stars. Due to the high-density and low-temperature regime in these stars, the interaction between quarks through gluon exchange could favor the appearance of a color superconducting state, significantl modifying the equation of state of the system. In this paper we present a general overview of this Subject, taking also into account the effect of strong magnetic field in the quark stars
Magnetic Field and Temperature Effects on Strangelets
The main properties of magnetized strangelets, namely, their energy per baryon, radius and electric charge, are studied in the unpaired strange quark matter phase. Temperature effects are taken into account in order to study their stability compared to the (56)Fe isotope and non-magnetized strangelets within the framework of the MIT bag model. It is concluded that the presence of a magnetic field tends to stabilize more the strangelets, even when temperature is considered. We find that the electric charge is modified in the presence of the magnetic field, leading to higher charge values for magnetized strangelets, when compared to the non-magnetized case
Neutrinos and the matter-antimatter asymmetry in the Universe
The discovery of neutrino oscillations provides a solid evidence for nonzero
neutrino masses and leptonic mixing. The fact that neutrino masses are so tiny
constitutes a puzzling problem in particle physics. From the theoretical
viewpoint, the smallness of neutrino masses can be elegantly explained through
the seesaw mechanism. Another challenging issue for particle physics and
cosmology is the explanation of the matter-antimatter asymmetry observed in
Nature. Among the viable mechanisms, leptogenesis is a simple and
well-motivated framework. In this talk we briefly review these aspects, making
emphasis on the possibility of linking neutrino physics to the cosmological
baryon asymmetry originated from leptogenesis.Comment: 8 pages, 1 table, 1 figure; Based on talk given at the Symposium
STARS2011, 1 - 4 May 2011, Havana, Cuba; to be published in the Proceeding
Evolution, Metabolism and Molecular Mechanisms Underlying Extreme Adaptation of Euryarchaeota and Its Biotechnological Potential
Archaeal organisms harbor many unique genotypic and phenotypic properties, testifying their peculiar evolutionary status. Thus, the so‐called extremophiles must be adequately adapted to cope with many extreme environments with regard to metabolic processes, biological functions, genomes, and transcriptomes to overcome the challenges of life. This chapter will illustrate recent progress in the research on extremophiles from the phylum Euryarchaeota and compile their evolutive history, metabolic strategies, lipid composition, the structural adaptations of their enzymes to temperature, salinity, and pH and their biotechnological applications. Archaeal organisms have evolved to deal with one or more extreme conditions, and over the evolution, they have accumulated changes in order to optimize protein structure and enzyme activity. The structural basis of these adaptations resulted in the construction of a vast repertoire of macromolecules with particular features not found in other organisms. This repertoire can be explored as an inexhaustible source of biological molecules for industrial or biotechnological applications. We hope that the information compiled herein will open new research lines that will shed light on various aspects of these extremophilic microorganisms. In addition, this information will be a valuable resource for future studies looking for archaeal enzymes with particular properties
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