160 research outputs found
Superspace evaluation of the two-loop effective potential for the O'Raifeartaigh model
All-order spurion-corrected superpropagators and superfield Feynman rules are
employed to systematically compute a two-loop corrected effective potential for
the O'Raifeartaigh model, that realizes spontaneous supersymmetry breaking.
Though the shifted superpropagators are rather nontrivial, superspace
techniques may be suitably extended and confirm their efficacy in computing
radiative corrections even when supersymmetry breakdown occurs.Comment: 24 pages, 2 figures, revtex4, 2 pages added, new appendix adde
Supergraph Approach in a Higher-order LDE Calculation of the Effective Potential for F-type Broken SUSY
In this work, we adopt the simplest model that spontaneously breaks
supersymmetry, namely, the minimal O'Raifeartaigh model. The effective
potential is computed in the framework of the linear delta expansion (LDE)
approach up to the order , conjugated with superspace and supergraph
techniques. The latter can be duly mastered even if supersymmetry is no longer
exact and the efficacy of the superfield approach in connection with the LDE
procedure is confirmed according to our investigation. That opens up a way for
a semi-nonperturbative superspace computation which allows us to deal with
spontaneously broken supersymmetric models and encourages us to go further and
apply this treatment to the Minimal Supersymmetric Standard Model (MSSM)
precision tests.Comment: 42 pages, 22 figures, text modified, new paragraph added in the
conclusions, revtex
Superspace approach to the renormalization of the O'Raifeartaigh model up to the second order in the LDE parameter
We adopt a superspace/supergraph formalism to pursue the investigation of the
structure of one- and two-loop divergences in the frame of the minimal
O'Raifeartaigh model that realizes the F-term spontaneous supersymmetry
breaking. The linear delta expansion(LDE) procedure is introduced and
renormalization is carried out up to the second order in the LDE expansion
parameter. In agreement with the nonrenormalization theorem for the
(chiral/antichiral) matter potential of supersymmetry,
our explicit supergraph calculations confirm that only the K\"{a}hler potential
is actually renomalized.Comment: 23 pages, 4 figures, revtex4. arXiv admin note: text overlap with
arXiv:0904.467
Linear delta expansion applied to the O'Raifeartaigh model
We reassess the method of the linear delta expansion for the calculation of
effective potentials in superspace, by adopting the improved version of the
super-Feynman rules in the framework of the O'Raifeartaigh model for
spontaneous supersymmetry breaking. The effective potential is calculated using
both the fastest apparent convergence and the principle of minimal sensitivity
criteria and the consistency and efficacy of the method are checked in deriving
the Coleman-Weinberg potential.Comment: 20 pages, 2 figures, revtex4, revised and extended, published versio
Mass dimension one fermions and their gravitational interaction
We investigate in detail the interaction between the spin- fields
endowed with mass dimension one and the graviton. We obtain an interaction
vertex that combines the characteristics of scalar-graviton and Dirac's
fermion-graviton vertices, due to the scalar-dynamic attribute and the
fermionic structure of this field. It is shown that the vertex obtained obeys
the Ward-Takahashi identity, ensuring the gauge invariance for this
interaction. In the contribution of the mass dimension one fermion to the
graviton propagator at one-loop, we found the conditions for the cancellation
of the tadpole term by a cosmological counter-term. We calculate the scattering
process for arbitrary momentum. For low energies, the result reveals that only
the scalar sector present in the vertex contributes to the gravitational
potential. Finally, we evaluate the non relativistic limit of the gravitational
interaction and obtain an attractive Newtonian potential, as required for a
dark matter candidate.Comment: 8 pages, 3 figure
Mother-to-child transmission of human immunodeficiency virus in aten years period
<p>Abstract</p> <p>Objectives</p> <p>to evaluate mother-to-child transmission (MTCT) rates and related factors in HIV-infected pregnant women from a tertiary hospital between 2000 and 2009.</p> <p>Subjects and method</p> <p>cohort of 452 HIV-infected pregnant women and their newborns. Data was collected from recorded files and undiagnosed children were enrolled for investigation. Statistical analysis: qui-square test, Fisher exact test, Student <it>t </it>test, Mann-Whitney test, ANOVA, risk ratio and confidence intervals.</p> <p>Results</p> <p>MTCT occurred in 3.74%. The study population displayed a mean age of 27 years; 86.5% were found to have acquired HIV through sexual contact; 55% were aware of the diagnosis prior to the pregnancy; 62% were not using HAART. Mean CD4 cell-count was 474 cells/ml and 70.3% had undetectable viral loads in the third trimester. HAART included nevirapine in 35% of cases and protease inhibitors in 55%; Zidovudine monotherapy was used in 7.3%. Mean gestational age at delivery was 37.2 weeks and in 92% by caesarian section; 97.2% received intravenous zidovudine. Use of AZT to newborn occurred in 100% of them. Factors identified as associated to MTCT were: low CD4 cell counts, elevated viral loads, maternal AIDS, shorter periods receiving HAART, other conditions (anemia, IUGR (intra uterine growth restriction), oligohydramnium), coinfecctions (CMV and toxoplasmosis) and the occurrence of labor. Use of HAART for longer periods, caesarian and oral zidovudine for the newborns were associated with a decreased risk. Poor adhesion to treatment was present in 13 of the 15 cases of transmission; in 7, coinfecctions were diagnosed (CMV and toxoplasmosis).</p> <p>Conclusion</p> <p>Use of HAART and caesarian delivery are protective factors for mother-to-child transmission of HIV. Maternal coinfecctions and other conditions were risk factors for MTCT.</p
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