Top-quark and neutrino composite Higgs bosons

In the context of top-quark condensation models, the top-quark alone is too light to saturate the correct value of the electroweak scale by its condensate. Within the seesaw scenario the neutrinos can have their Dirac masses large enough so that their condensates can provide significant contribution to the value of the electroweak scale. We address the question of a phenomenological feasibility of the top-quark and neutrino condensation conspiracy against the electroweak symmetry. Mandatory is to reproduce the masses of electroweak gauge bosons, the top-quark mass and the recently observed scalar mass of $125\,\mathrm{GeV}$ and to satisfy the upper limits on absolute value of active neutrino masses. To accomplish that we design a reasonably simplified effective model with two composite Higgs doublets. Additionally, we work with a general number $N$ of right-handed neutrino flavor triplets participating on the seesaw mechanism. There are no experimental constraints limiting this number. The upper limit is set by the model itself. Provided that the condensation scale is of order $10^{17-18}\,\mathrm{GeV}$ and the number of right-handed neutrinos is ${\cal O}(100-1000)$, the model predicts masses of additional Higgs bosons below $250\,\mathrm{GeV}$ and a suppression of the top-quark Yukawa coupling to the $125\,\mathrm{GeV}$ particle at the $\sim60\,$ level of the Standard model value.Comment: 12 pages, 4 figures, this third version is the one having been published in EPJ

Towards interferometry of neutrino electromagnetism

It is predicted within the Standard Model of elementary particles that asymmetric neutrino environments cause rotation of linear polarization of electromagnetic wave -- the birefringence. We demonstrate that this effect is strongly enhanced if additionally the photon is propagating through refractive medium, which effectively increases the photon exposure to the neutrino medium. Our estimate for infrared laser beam in $1\,\mathrm{m}$ long optical fiber exposed to reactor anti-neutrino flux results in linear polarization rotation by the angle $\sim4.6\times10^{-39}\,\mathrm{rad}$. We also derive the proper dependence of the effect on the angle between the directions of photon and neutrino propagation in the laboratory frame. For that purpose we derive the correct form of the basis of polarization four-vectors, which differs from the one widely used in literature. We also estimate the sub-leading optical effect of the neutrino medium due to the neutrino dipole magnetic moment, in terms of a variation of the refractive index and its angular dependence. A rough monochromatic approximation points towards the existence of a resonant enhancement of the effect.Comment: 6 pages, 1 figur

0νββ and 2νββ nuclear matrix elements evaluated in closure approximation, neutrino potentials and SU(4) symmetry

The intimate relation between the Gamow-Teller part of the matrix element M^(0ν)_(GT) and the 2νββ closure matrix element M^(2ν)_(cl) is explained and explored. If the corresponding radial dependence C^(2ν)_(cl)(r) would be known, M^(0ν) corresponding to any mechanism responsible for the 0νββ decay can be obtained as a simple integral. However, the M^(2ν)_(cl) values, and therefore also the functions C^(2ν)_(cl)(r), sensitively depend not only on the properties of the first few 1^+ states but also of higher-lying 1^+ states in the intermediate odd-odd nuclei. We show that the β^− and β^+ amplitudes of such states typically have opposite relative signs, and their contributions reduce severally the M^(2ν)_(cl) values. We suggest that demanding that M^(2ν)_(cl) = 0 is a sensible alternative way, within the QRPA method, of determining the amount of renormalization of isoscalar particle-particle interaction strength g^(T=0)_(pp). Using such prescription, the matrix elements M^(0ν) are evaluated; their values are not very different (≤ 20%) from the usual QRPA values when g^(T=0)_(pp) is related to the known 2νββ half-lives. We note that vanishing values of M^(2ν)_(cl) are signs of a partial restoration of the spin-isospin SU(4) symmetry

0νββ and 2νββ nuclear matrix elements evaluated in closure approximation, neutrino potentials and SU(4) symmetry

The intimate relation between the Gamow-Teller part of the matrix element M^(0ν)_(GT) and the 2νββ closure matrix element M^(2ν)_(cl) is explained and explored. If the corresponding radial dependence C^(2ν)_(cl)(r) would be known, M^(0ν) corresponding to any mechanism responsible for the 0νββ decay can be obtained as a simple integral. However, the M^(2ν)_(cl) values, and therefore also the functions C^(2ν)_(cl)(r), sensitively depend not only on the properties of the first few 1^+ states but also of higher-lying 1^+ states in the intermediate odd-odd nuclei. We show that the β^− and β^+ amplitudes of such states typically have opposite relative signs, and their contributions reduce severally the M^(2ν)_(cl) values. We suggest that demanding that M^(2ν)_(cl) = 0 is a sensible alternative way, within the QRPA method, of determining the amount of renormalization of isoscalar particle-particle interaction strength g^(T=0)_(pp). Using such prescription, the matrix elements M^(0ν) are evaluated; their values are not very different (≤ 20%) from the usual QRPA values when g^(T=0)_(pp) is related to the known 2νββ half-lives. We note that vanishing values of M^(2ν)_(cl) are signs of a partial restoration of the spin-isospin SU(4) symmetry

Low-scale seesaw from neutrino condensation

Knowledge of the mechanism of neutrino mass generation would help understand a lot more about Lepton Number Violation (LNV), the cosmological evolution of the Universe, or the evolution of astronomical objects. Here we propose a verifiable and viable extension of the Standard model for neutrino mass generation, with a low-scale seesaw mechanism via LNV condensation in the sector of sterile neutrinos. To prove the concept, we analyze a simplified model of just a single family of elementary particles and check it against a set of phenomenological constraints coming from electroweak symmetry breaking, neutrino masses, leptogenesis and dark matter. The model predicts (i) TeV scale quasi-degenerate heavy sterile neutrinos, suitable for leptogenesis with resonant enhancement of the CP asymmetry, (ii) a set of additional heavy Higgs bosons whose existence can be challenged at the LHC, (iii) an additional light and sterile Higgs scalar which is a candidate for decaying warm dark matter, and (iv) a majoron. Since the model is based on simple and robust principles of dynamical mass generation, its parameters are very restricted, but remarkably it is still within current phenomenological limitsIndexación: Scopu