18,332 research outputs found
Renormalization Group and Conformal Symmetry Breaking in the Chern-Simons Theory Coupled to Matter
The three-dimensional Abelian Chern-Simons theory coupled to a scalar and a
fermionic field of arbitrary charge is considered in order to study conformal
symmetry breakdown and the effective potential stability. We present an
improved effective potential computation based on two-loop calculations and the
renormalization group equation: the later allows us to sum up series of terms
in the effective potential where the power of the logarithms are one, two and
three units smaller than the total power of coupling constants (i.e., leading,
next-to-leading and next-to-next-to-leading logarithms). For the sake of this
calculation we determined the beta function of the
fermion-fermion-scalar-scalar interaction and the anomalous dimension of the
scalar field. We shown that the improved effective potential provides a much
more precise determination of the properties of the theory in the broken phase,
compared to the standard effective potential obtained directly from the loop
calculations. This happens because the region of the parameter space where
dynamical symmetry breaking occurs is drastically reduced by the improvement
discussed here.Comment: 29 pages, 10 figures, 1 tabl
An Model for Lepton Mass Matrices with Nearly Minimal Texture
We propose a simple extension of the electroweak standard model based on the
discrete symmetry that is capable of realizing a nearly minimal
Fritzsch-type texture for the Dirac mass matrices of both charged leptons and
neutrinos. This is achieved with the aid of additional and
symmetries, one of which can be embedded in . Five complex scalar
singlet fields are introduced in addition to the SM with right-handed
neutrinos. Although more general, the modified texture of the model retains the
successful features of the minimal texture without fine-tuning; namely, it
accommodates the masses and mixing of the leptonic sector and relates the
emergence of large leptonic mixing angles with the seesaw mechanism. For large
deviations of the minimal texture, both quasidegenerate spectrum or inverted
hierarchy are allowed for neutrino masses.Comment: 11pp, 2 figures. v2: vev alignment addressed, additional analysis
performed; to appear in PR
Non-perturbative fixed points and renormalization group improved effective potential
The stability conditions of a renormalization group improved effective
potential have been discussed in the case of scalar QED and QCD with a
colorless scalar. We calculate the same potential in these models assuming the
existence of non-perturbative fixed points associated to a conformal phase. In
the case of scalar QED the barrier of instability found previously is barely
displaced as we approach the fixed point, and in the case of QCD with a
colorless scalar not only the barrier is changed but the local minimum of the
potential is also changed.Comment: 6 pages, 8 figures, References added. Matching the journal versio
Closing the Symmetry at Electroweak Scale
We show that some models with gauge
symmetry can be realized at the electroweak scale and that this is a
consequence of an approximate global symmetry. This symmetry
implies a condition among the vacuum expectation value of one of the neutral
Higgs scalars, the 's coupling constant, , the sine of the weak
mixing angle , and the mass of the boson, . In the limit
in which this symmetry is valid it avoids the tree level mixing of the
boson of the Standard Model with the extra boson. We have verified
that the oblique parameter is within the allowed range indicating that the
radiative corrections that induce such a mixing at the 1-loop level are small.
We also show that a custodial symmetry implies that in some of
the models we have to include sterile (singlets of the 3-3-1 symmetry)
right-handed neutrinos with Majorana masses, being the see-saw mechanism
mandatory to obtain light active neutrinos. Moreover, the approximate
symmetry implies that the extra non-standard
particles of these 3-3-1 models can be considerably lighter than it had been
thought before so that new physics can be really just around the corner.Comment: 32 pages, no figure, RevTeX. Some typos correcte
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