1,625 research outputs found
Warped brane-world compactification with Gauss-Bonnet term
In the Randall-Sundrum (RS) brane-world model a singular delta-function
source is matched by the second derivative of the warp factor. So one should
take possible curvature corrections in the effective action of the RS models in
a Gauss-Bonnet (GB) form. We present a linearized treatment of gravity in the
RS brane-world with the Gauss-Bonnet modification to Einstein gravity. We give
explicit expressions for the Neumann propagator in arbitrary D dimensions and
show that a bulk GB term gives, along with a tower of Kaluza-Klein modes in the
bulk, a massless graviton on the brane, as in the standard RS model. Moreover,
a non-trivial GB coupling can allow a new branch of solutions with finite
Planck scale and no naked bulk singularity, which might be useful to avoid some
of the previously known ``no--go theorems'' for RS brane-world
compactifications.Comment: 23 pages, typos in Secs. 5 & 6 corrected, expanded/published version
(IJMPA
Field Screening of Lentil Genotypes Against Aphid Infestation in Inner Tarai of Nepal
Twenty lentil (Lens culinaris Medik) genotypes received from Grain Legumes Research Program, Khajura, Banke were screened for relative tolerance against aphid (Aphis craccivora Koch.) at the research field of National Maize Research Program, Rampur, Chitwan during winter seasons of two consecutive years 2016 and 2017. The design of the experiment was Randomized Complete Block having three replications. The unit plot size was 4m × 1 m with 25cm row to row spacing and continue plant to plant spacing was maintained and net harvested plot was 4 square meters. The recommended dose of fertilizer was 20:40:20 N:P2O5:K2O kg/ha and seed rate 30 kg/ha. Insect data were collected based on aphid population found at apical twigs (10 cm) per plant and scoring was done during flowering and pod formation stage. The grain yield was recorded. All screened genotypes differed significantly (p<0.05) on aphid population and grain yield. Genotypes, ILL 9924, RL 83, ILL 10856, ILL 6458 and RL 67 were less susceptible with higher grain yield. These results have important implications for the development of aphid tolerant high yielding lentil variety in inner Tarai of Nepal
Reconstructing a model of quintessential inflation
We present an explicit cosmological model where inflation and dark energy
both could arise from the dynamics of the same scalar field. We present our
discussion in the framework where the inflaton field attains a nearly
constant velocity (where
is the e-folding time) during inflation. We show that the model
with and can easily satisfy inflationary constraints,
including the spectral index of scalar fluctuations (),
tensor-to-scalar ratio () and also the bound imposed on
during the nucleosynthesis epoch (). In our
construction, the scalar field potential always scales proportionally to the
square of the Hubble expansion rate. One may thereby account for the two vastly
different energy scales associated with the Hubble parameters at early and late
epochs. The inflaton energy could also produce an observationally significant
effective dark energy at a late epoch without violating local gravity tests.Comment: 18 pages, 7 figures; added refs, published versio
Evaluation of Barley Genotypes Against Spot Blotch Disease in Inner Tarai Region of Nepal
Spot blotch caused by Bipolaris sorokiniana (Sacc. in Sorok.) Shoem. is an important disease of barley (Hordeum vulgare L.). A total of 126 barley genotypes received from Hill Crops Research Program, Kabre, Dolakha having SoluUwa as a susceptible check and Bonus as a resistant check were evaluated as barley disease screening nursery (BDSN) under natural epiphytotic condition at National Maize Research Program, Rampur, Chitwan during winter seasons of 2017 and 2018. The nursery was planted in augmented design. The resistant and susceptible checks were repeated and planted after each 10 tested entries. The unit plot size was 2 rows of one meter length for each genotype planted continuously with 25cm row to row spacing. The seed rate was 100 kg/ha. The recommended fertilizer dose of 23:30:0 N:P2O5:K2O kg/ha was applied. The double digit scale (00 to 99) was used to measure overall foliar infection on the whole plant during flowering, soft dough and hard dough stages. Other agronomic practices were followed as per recommendation. Genotypes B86019-1K-3K-0K3, ACC 2087, ACC 2441, ACC GHv-06816, ACC 1597, ACC 1612, ACC 2059 and ACC 2032 were resistant against spot blotch disease. Similarly, 32 barley genotypes were moderately resistant and rest of the tested genotypes were susceptible to the disease. The selected resistant barley genotypes can be used in crossing program and/or promoted for further testing to develop spot blotch resistant varieties for inner Tarai region of Nepal
Warped compactification on curved manifolds
The characterization of a six- (or seven)-dimensional internal manifold with
metric as having positive, zero or negative curvature is expected to be an
important aspect of warped compactifications in supergravity. In this context,
Douglas and Kallosh recently pointed out that a compact internal space with
negative curvature could help to construct four-dimensional de Sitter solutions
only if the extra dimensions are strongly warped or there are large stringy
corrections. That is, the problem of finding 4-dimensional de Sitter solutions
is well posed, if all extra dimensions are physically compact, which is called
a no-go theorem. Here, we show that the above conclusion does not extend to a
general class of warped compactifications in classical supergravity that allow
a non-compact direction or cosmological solutions for which the internal space
is asymptotic to a cone over a product of compact Einstein spaces or spheres.
For clarity, we present classical solutions that compactify higher-dimensional
spacetime to produce a Robertson--Walker universe with de Sitter-type expansion
plus one extra non-compact direction. Such models are found to admit both an
effective four-dimensional Newton constant that remains finite and a
normalizable zero-mode graviton wavefunction. We also exhibit the possibility
of obtaining 4D de Sitter solutions by including the effect of fluxes (p-form
field strengths).Comment: 24 pages, 1 figure; v5 significant changes in the presentation,
published (journal) versio
Comparative Study of Impact of Azotobacter and Trichoderma with Other Fertilizers on Maize Growth
Biofertilizers may be a better eco-friendly option to maintain soil fertility. The study was conducted to investigate the effect of Azotobacter and Trichoderma on the vegetative growth of maize (Zea mays L.) plants. The experiment was carried out in medium sized pots, at IAAS, Lamjung (Feb 2017 - May 2017) in completely randomized design (CRD), consisting eight treatments and three replications. Treatments were namely T1 (control), T2 (Azotobacter), T3 (Trichoderma), T4 (Azotobacter + Trichoderma), T5 (NPK), T6 (Azotobacter + Trichoderma + FYM), T7 (Azotobacter + Trichoderma + FYM + NPK), T8 (FYM). Azotobacter showed a positive increase in plant height, stem girth, dry shoot weight, root length and width, and root weight while Trichoderma displayed either negative or minimal impact. Effect of FYM was lower than Azotobacter but considerably higher than Trichoderma. Trichoderma seriously inhibited the expression of Azotobacter when used together. Trichoderma even suppressed the outcome (except shoot weight) of FYM when used together. Root length was the longest in Azotobacter inoculation. The highest number of leaves was in T7 followed by Azotobacter (T2) and NPK (T5). Unlike leaf width, Azotobacter showed a negligible increase in leaves length while Trichoderma wherever present showed the negative impact. Minimum chlorophyll content was found in Azotobacter or Trichoderma after 73 days. Azotobacter treatment showed early tasseling than Trichoderma. The association of Azotobacter and Trichoderma increased the biomass. Azotobacter has significant effects on growth parameters of maize and can supplement chemical fertilizer, while Trichoderma was found to inhibit most of the growth parameters
On compatibility of string effective action with an accelerating universe
In this paper, we fully investigate the cosmological effects of the moduli
dependent one-loop corrections to the gravitational couplings of the string
effective action to explain the cosmic acceleration problem in early (and/or
late) universe. These corrections comprise a Gauss-Bonnet (GB) invariant
multiplied by universal non-trivial functions of the common modulus
and the dilaton . The model exhibits several features of cosmological
interest, including the transition between deceleration and acceleration
phases. By considering some phenomenologically motivated ansatzs for one of the
scalars and/or the scale factor (of the universe), we also construct a number
of interesting inflationary potentials. In all examples under consideration, we
find that the model leads only to a standard inflation () when the
numerical coefficient associated with modulus-GB coupling is positive,
while the model can lead also to a non-standard inflation (), if
is negative. In the absence of (or trivial) coupling between the GB term and
the scalars, there is no crossing between the phases, while
this is possible with non-trivial GB couplings, even for constant dilaton phase
of the standard picture. Within our model, after a sufficient amount of e-folds
of expansion, the rolling of both fields and can be small. In
turn, any possible violation of equivalence principle or deviations from the
standard general relativity may be small enough to easily satisfy all
astrophysical and cosmological constraints.Comment: 30 pages, 8 figures; v2 significant changes in notations, appendix
and refs added; v3 significant revisions, refs added; v4 appendix extended,
new refs, published versio
No Go Theorem for Self Tuning Solutions With Gauss-Bonnet Terms
We consider self tuning solutions for a brane embedded in an anti de Sitter
spacetime. We include the higher derivative Gauss-Bonnet terms in the action
and study singularity free solutions with finite effective Newton's constant.
Using the methods of Csaki et al, we prove that such solutions, when exist,
always require a fine tuning among the brane parameters. We then present a new
method of analysis in which the qualitative features of the solutions can be
seen easily without obtaining the solutions explicitly. Also, the origin of the
fine tuning is transparent in this method.Comment: 17 pages, 3 figure
Accelerating universe from warped extra dimensions
Accelerating universe or the existence of a small and positive cosmological
constant is probably the most pressing obstacle as well as opportunity to
significantly improving the models of four-dimensional cosmology from
fundamental theories of gravity, including string theory. In seeking to resolve
this problem, one naturally wonders if the real world can somehow be
interpreted as an inflating de Sitter brane embedded in a higher-dimensional
spacetime described by warped geometry. In this scenario, the four-dimensional
cosmological constant may be uniquely determined in terms of two length scales:
one is a scale associated with the size of extra dimensions and the other is a
scale associated with the expansion rate of our universe. In some specific
cases, these two scales are complementary to each other. This result is
demonstrated here by presenting some explicit and completely non-singular de
Sitter space dS solutions of vacuum Einstein equations in five and ten
dimensions.Comment: 7 pages; extended (from journal) version, minor typos fixed, refs
adde
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