4,344 research outputs found
Suppression of Higgsino mediated proton decay by cancellations in GUTs and strings
A mechanism for the enhancement for proton lifetime in
supersymmetric/supergravity (SUSY/SUGRA) grand unified theories (GUTs) and in
string theory models is discussed where Higgsino mediated proton decay arising
from color triplets (anti-triplets) with charges and
is suppressed by an internal cancellation due to contributions
from different sources. We exhibit the mechanism for an SU(5) model with
Higgs multiplets in addition to the usual Higgs structure of
the minimal model. This model contains both and
Higgs color triplets (anti-triplets) and simple constraints allow for a
complete suppression of Higgsino mediated proton decay. Suppression of proton
decay in an SU(5) model with Planck scale contributions is also considered. The
suppression mechanism is then exhibited for an SO(10) model with a unified
Higgs structure involving representations.The SU(5)
decomposition of contains and
and the cancellation mechanism arises among these
contributions which mirrror the SU(5) case. The cancellation mechanism appears
to be more generally valid for a larger class of unification models.
Specifically the cancellation mechanism may play a role in string model
constructions to suppress proton decay from dimension five operators. The
mechanism allows for the suppression of proton decay consistent with current
data allowing for the possibility that proton decay may be visible in the next
round of nucleon stability experiment.Comment: 26 pages, no figures. Revtex 4. To appear in Physical Review
State-space Correlations and Stabilities
The state-space pair correlation functions and notion of stability of
extremal and non-extremal black holes in string theory and M-theory are
considered from the viewpoints of thermodynamic Ruppeiner geometry. From the
perspective of intrinsic Riemannian geometry, the stability properties of these
black branes are divulged from the positivity of principle minors of the
space-state metric tensor. We have explicitly analyzed the state-space
configurations for (i) the two and three charge extremal black holes, (ii) the
four and six charge non-extremal black branes, which both arise from the string
theory solutions. An extension is considered for the ---
multi-centered black branes, fractional small black branes and two charge
rotating fuzzy rings in the setup of Mathur's fuzzball configurations. The
state-space pair correlations and nature of stabilities have been investigated
for three charged bubbling black brane foams, and thereby the M-theory
solutions are brought into the present consideration. In the case of extremal
black brane configurations, we have pointed out that the ratio of diagonal
space-state correlations varies as inverse square of the chosen parameters,
while the off diagonal components vary as inverse of the chosen parameters. We
discuss the significance of this observation for the non-extremal black brane
configurations, and find similar conclusion that the state-space correlations
extenuate as the chosen parameters are increased.Comment: 35 pages, Keywords: Black Hole Physics, Higher-dimensional Black
Branes, State-space Correlations and Statistical Configurations. PACS
numbers: 04.70.-s Physics of black holes; 04.70.Bw Classical black holes;
04.70.Dy Quantum aspects of black holes, evaporation, thermodynamics;
04.50.Gh Higher-dimensional black holes, black strings, and related object
Electronic structure of spin 1/2 Heisenberg antiferromagnetic systems: Ba_2Cu(PO_4)_2 and Sr_2Cu(PO_4)_2
We have employed first principles calculations to study the electronic
structure and magnetic properties of the low-dimensional phosphates,
Ba2Cu(PO4)2 and Sr2Cu(PO4)2. Using the self-consistent tight-binding lin-
earized muffin-tin orbital method and the Nth order muffin-tin orbital method,
we have calculated the various intrachain as well as the interchain hopping
parameters between the magnetic ions Cu2+ for both the com- pounds. We find
that the nearest-neighbor intrachain hopping t is the dominant interaction
suggesting the compounds to be indeed one dimensional. Our analysis of the band
dispersion, orbital projected band struc- tures, and the hopping parameters
confirms that the Cu2+-Cu2+ super-super exchange interaction takes place along
the crystallographic b direction mediated by O-P-O. We have also analyzed in
detail the origin of short-range exchange interaction for these systems. Our ab
initio estimate of the ratio of the exchange inter- action of Sr2Cu(PO4)2 to
that of Ba2Cu(PO4)2 compares excellently with available experimental results.Comment: 6 pages, 4 figure
Natural emergence of antigen-reactive T cells in lepromatous leprosy patients during Erythema nodosum leprosum.
Fifteen lepromatous leprosy (LL) patients undergoing erythema nodosum leprosum (ENL) reactions were compared with 13 stable, uncomplicated, anergic individuals of the same leprosy background. ENL patients showed significant antigen-induced leukocyte migration inhibition (migration index = 0.058 ± 0.01), paralleling the values obtained with a responder tuberculoid leprosy population (migration index = 0.04 ± 0.004). Both phytohemagglutinin-induced general T-cell proliferation and, more significantly, antigen-induced lymphoproliferation were enhanced during the acute phase of the reaction. Suppressor cell activity, monitored by a costimulant assay, showed enhanced antigen-stimulated suppression of mitogen responses. Interestingly, the improvement in in vitro T-cell responses was not reflected in dermal reactivity, since 48-h delayed-type hypersensitivity responses after intradermal injection of soluble Mycobacterium leprae antigens continued to be poor. After subsidence of reactional lesions, leukocyte migration inhibition, lymphoproliferation, and suppressor cell activity were reduced to the unresponsive state seen in stable LL patients. Significantly, perturbations of T-cell reactivity are detectable in ENL reactions, indicating the natural but transient emergence of antigen-induced T cells in LL
Hindered magnetic order from mixed dimensionalities in CuPO
We present a combined experimental and theoretical study of the spin-1/2
compound CuPO that features a network of two-dimensional (2D)
antiferromagnetic (AFM) square planes, interconnected via one-dimensional (1D)
AFM spin chains. Magnetic susceptibility, high-field magnetization, and
electron spin resonance (ESR) data, as well as microscopic density-functional
band-structure calculations and subsequent quantum Monte-Carlo simulations,
show that the coupling 40 K in the layers is an order of magnitude
larger than 4 K in the chains. Below 8 K, CuPO
develops long-range order (LRO), as evidenced by a weak net moment on the 2D
planes induced by anisotropic magnetic interactions of Dzyaloshinsky-Moriya
type. A striking feature of this 3D ordering transition is that the 1D moments
grow significantly slower than the ones on the 2D layers, which is evidenced by
the persistent paramagnetic ESR signal below . Compared to typical
quasi-2D magnets, the ordering temperature of CuPO 0.2
is unusually low, showing that weakly coupled spins sandwiched between 2D
magnetic units effectively decouple these units and impede the long-range
ordering.Comment: 11 pages, 12 figures, 1 table; published version with few additional
citations added and misprints fixe
Testing Supergravity Grand Unification at Future Accelerator and Underground Experiments
The full parameter space of supergravity grand unified theory with
type proton decay is analysed using renormalization
group induced electroweak symmetry breaking under the restrictions that the
universal scalar mass and gluino mass are TeV (no extreme fine
tuning) and the Higgs triplet mass obeys . Future proton
decay experiments at SuperKamiokande or ICARUS can reach a sensitivity for the
mode of yr allowing a number of
predictions concerning the SUSY mass spectrum. Thus either the decay mode will be seen at these experiments or a
chargino of mass GeV will exist and hence be observable
at LEP2. Further, if yr,
then either the light Higgs has mass GeV or GeV i.e. either the light Higgs or the light chargino (or both) would be
observable at LEP2. Thus, the combination of future accelerator and future
underground experiments allow for strong experimental tests of this theory.Comment: 7 figures available upon request, CTP-TAMU-32/93, NUB-TH-3066/93 and
SSCL-Preprint-44
Genetic diversity analysis of mustard (Brassica spp.) germplasm using molecular marker for selection of short duration genotypes
Molecular characterization of 16 mustard (Brassica spp.) genotypes by using 12 RAPD markers revealed that three primers GLA-11, OPB-04 and OPD-02 showed good technical resolution and sufficient variations among different genotypes. A total of 40 RAPD bands were scored of which 38 (94.87%) polymorphic amplification products were obtained. Besides, the primer OPD-02 amplified maximum number of polymorphic bands (100.00%) while the primer GLA-11 and OPB-04 generated the least (92.31%) polymorphic bands, which were minimal in number. The present study produced 13.33 scorable bands per primer and 12.67 polymorphic bands per primer. Frequencies of maximum number of polymorphic loci were found to be high with the exception of GLA-11(0.750), OPB-04 (0.875) and OPD-02 (0.750). The estimate of Nei's genetic diversity for the entire genotypes of mustard was 0.3596 and Shannon's information index was 0.535. There was a high level of genetic variation among the mustard genotypes studied from the proportion of polymorphic loci point of view. The values of pair-wise comparison of Nei’s genetic distance between genotypes were computed from combined data for the three primers; ranged from 0.1054 to 0.9862. BINA Sarisha-3 and BINA Sarisha-4 showed the lowest genetic distance of 0.1054 where Tori-7 and NAP-0758-2 showed highest genetic distance of 0.9862. The 16 mustard genotypes were differentiated into three main clusters: BARI Sarisha-14, BARI Sarisha-9, BARI Sarisha-15, BINA Sarisha-4, BINA Sarisha-3, BARI Sarisha-8, Sampad and Tori-7 in cluster A, NAP-0763, NAP-0721-1, BARI Sarisha-4, BARI Sarisha-6, NAP-0762-2 and NAP-0848-2 in cluster B and NAP-0838 and NAP-0758-2 were grouped into cluster C by making dendrogram based on Nei’s genetic distance using unweighted pair group method of arithmetic means (UPGMA).Keywords: Mustard, diversity analysis, RAPD marker, genetic distance, cluster analysis.Abbreviation: UPGMA, Unweighted pair group method of arithmetic means; RFLP, restriction fragment length polymorphism; RAPDs, random amplified polymorphic DNAs; AFLP, amplified fragment length polymorphism; SSRs, simple sequence repeats; CTAB, cetyl trimethyl ammonium bromide.
Synthesis, Structure and Properties of Tetragonal Sr2M3As2O2 (M3 = Mn3, Mn2Cu and MnZn2) Compounds Containing Alternating CuO2-Type and FeAs-Type Layers
Polycrystalline samples of Sr2Mn2CuAs2O2, Sr2Mn3As2O2, and Sr2Zn2MnAs2O2 were
synthesized. Their temperature- and applied magnetic field-dependent
structural, transport, thermal, and magnetic properties were characterized by
means of x-ray and neutron diffraction, electrical resistivity rho, heat
capacity, magnetization and magnetic susceptibility measurements. These
compounds have a body-centered-tetragonal crystal structure (space group
I4/mmm) that consists of MO2 (M = Zn and/or Mn) oxide layers similar to the
CuO2 layers in high superconducting transition temperature Tc cuprate
superconductors, and intermetallic MAs (M = Cu and/or Mn) layers similar to the
FeAs layers in high-Tc pnictides. These two types of layers alternate along the
crystallographic c-axis and are separated by Sr atoms. The site occupancies of
Mn, Cu and Zn were studied using Rietveld refinements of x-ray and neutron
powder diffraction data. The temperature dependences of rho suggest metallic
character for Sr2Mn2CuAs2O2 and semiconducting character for Sr2Mn3As2O2 and
Sr2Zn2MnAs2O2. Sr2Mn2CuAs2O2 is inferred to be a ferrimagnet with a Curie
temperature TC = 95(1) K. Remarkably, we find that the magnetic ground state
structure changes from a G-type antiferromagnetic structure in Sr2Mn3As2O2 to
an A-type ferrimagnetic structure in Sr2Mn2CuAs2O2 in which the Mn ions in each
layer are ferromagnetically aligned, but are antiferromagnetically aligned
between layers.Comment: 18 pages, 16 figures, 6 tables; submitted to Phys. Rev.
A Study of Insulin Resistance and its Clinico.Metabolic Associations Among Apparently Healthy Individuals Attending a Tertiary Care Hospital
Background: Insulin resistance (IR), as a result of unhealthy life.styles and westernization, most likely contributes to the increased incidence of metabolic abnormalities and consequently, the development of metabolic syndrome (MS). Aim: The present study was undertaken to determine the magnitude of IR and associated clinico.metabolic risk factors among the out-patients of a tertiary care hospital in Bihar, India. Subjects and Methods: Anthropometric profile, lipid profile, fasting blood glucose, C-reactive protein (CRP) and C-peptide of 112 individuals were measured using the standard procedures. IR was assessed using the homeostasis model (Homeostatic model assessment [HOMA]-IR).Results: The mean IR was 1.5 (1.0). Individuals with MS, higher body mass index and CRP ≥6 mg/l had higher IR. Linear regression showed, among the components of MS, waist circumference had the highest contribution toward IR. The optimal cut-off value to detect IR by HOMA2-IR was 1.35.Conclusion: IR was found to have a strong association with various clinico-metabolic risk factors. Keywords: C-reactive protein, Homeostatic model assessment insulin resistance, Insulin resistance, Metabolic syndrom
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