Modulational instability of ion-acoustic wave packets in quantum pair-ion plasmas

Amplitude modulation of quantum ion-acoustic waves (QIAWs) in a quantum electron-pair-ion plasma is studied. It is shown that the quantum coupling parameter $H$ (being the ratio of the plasmonic energy density to the Fermi energy) is ultimate responsible for the modulational stability of QIAW packets, without which the wave becomes modulational unstable. New regimes for the modulational stability (MS) and instability (MI) are obtained in terms of $H$ and the positive to negative ion density ratio $\beta$. The growth rate of MI is obtained, the maximum value of which increases with $\beta$ and decreases with $H$. The results could be important for understanding the origin of modulated QIAW packets in the environments of dense astrophysical objects, laboratory negative ion plasmas as well as for the next generation laser solid density plasma experiments.Comment: 4 pages, 2 figures (to appear in Astrophysics and Space Science

Oscillatory and asymptotic behaviour of a neutral differential equation with oscillating coefficients

In this paper, we obtain sufficient conditions so that every solution of $$\big(y(t)- \sum_{i=1}^n p_i(t) y(\delta_i(t))\big)'+\sum_{i=1}^m q_i(t) y(\sigma_i(t)) = f(t)$$ oscillates or tends to zero as $t \to \infty$. Here the coefficients $p_i(t), q_i(t)$ and the forcing term $f(t)$ are allowed to oscillate; such oscillation condition in all coefficients is very rare in the literature. Furthermore, this paper provides an answer to the open problem 2.8.3 in [7, p. 57]. Suitable examples are included to illustrate our results

New Black Hole Solutions in Brans-Dicke Theory of Gravity

Existence check of non-trivial, stationary axisymmetric black hole solutions in Brans-Dicke theory of gravity in different direction from those of Penrose, Thorne and Dykla, and Hawking is performed. Namely, working directly with the known explicit spacetime solutions in Brans-Dicke theory, it is found that non-trivial Kerr-Newman-type black hole solutions different from general relativistic solutions could occur for the generic Brans-Dicke parameter values -5/2\leq \omega <-3/2. Finally, issues like whether these new black holes carry scalar hair and can really arise in nature and if they can, what the associated physical implications would be are discussed carefully.Comment: 20 pages, no figure, Revtex, version to appear in Phys. Rev.

On 'Light' Fermions and Proton Stability in 'Big Divisor' D3/D7 Swiss Cheese Phenomenology

Building up on our earlier work [1,2], we show the possibility of generating "light" fermion mass scales of MeV-GeV range (possibly related to first two generations of quarks/leptons) as well as eV (possibly related to first two generations of neutrinos) in type IIB string theory compactified on Swiss-Cheese orientifolds in the presence of a mobile space-time filling D3-$brane restricted to (in principle) stacks of fluxed D7-branes wrapping the "big" divisor \Sigma_B. This part of the paper is an expanded version of the latter half of section 3 of a published short invited review [3] written up by one of the authors [AM]. Further, we also show that there are no SUSY GUT-type dimension-five operators corresponding to proton decay, as well as estimate the proton lifetime from a SUSY GUT-type four-fermion dimension-six operator to be 10^{61} years. Based on GLSM calculations in [1] for obtaining the geometric Kaehler potential for the "big divisor", using further the Donaldson's algorithm, we also briefly discuss in the first of the two appendices, obtaining a metric for the Swiss-Cheese Calabi-Yau used, that becomes Ricci flat in the large volume limit.Comment: v2: 1+25 pages, Title modified and text thoroughly expanded including a brief discussion on obtaining Ricci-flat Swiss Cheese Calabi-Yau metrics using the Donaldson's algorithm, references added, to appear in EPJ

Observable Neutron-Antineutron Oscillations in Seesaw Models of Neutrino Mass

We show that in a large class of supersymmetric models with spontaneously broken B-L symmetry, neutron--antineutron oscillations occur at an observable level even though the scale of B-L breaking is very high, v_{B-L} ~ 2 x 10^{16} GeV, as suggested by gauge coupling unification and neutrino masses. We illustrate this phenomenon in the context of a recently proposed class of seesaw models that solves the strong CP problem and the SUSY phase problem using parity symmetry. We obtain an upper limit on N-\bar{N} oscillation time in these models, \tau_{N-\bar{N}} < 10^{9} -10^{10} sec. This suggests that a modest improvement in the current limit on \tau_{N-\bar{N}} of 0.86 x 10^8 sec will either lead to the discovery of N-\bar{N} oscillations, or will considerably restrict the allowed parameter space of an interesting class of neutrino mass models.Comment: 11 pages RevTeX, 1 figur

Coupling Unification, GUT-Scale Baryogenesis and Neutron-Antineutron Oscillation in SO(10)

We show that unification of the three gauge couplings can be realized consistently in a class of non-supersymmetric SO(10) models with a one-step breaking to the Standard Model if a color-sextet scalar field survives down to the TeV scale. Such scalars, which should be accessible to the LHC for direct detection, arise naturally in SO(10) as remnants of the seesaw mechanism for neutrino masses. The diquark couplings of these scalars lead to \Delta B = 2 baryon number violating processes such as neutron-antineutron oscillation. We estimate the free neutron-antineutron transition time to be \tau_{n-\bar{n}} \approx (10^9-10^{12}) sec., which is in the interesting range for next generation n-\bar{n} oscillation experiments. These models also realize naturally the recently proposed (B-L)-violating GUT scale baryogenesis which survives to low temperatures unaffected by the electroweak sphaleron interactions.Comment: 15 pages, 4 eps figures, references added, to appear in Phys. Lett.

Vegetation dynamics under different management interventions in arid rangelands of Rajasthan

Watershed rangelands in Northern Afghanistan provide various ecosystem services that support the local people’s livelihoods, but they are now highly degraded essentially due to the continuous high grazing pressure and recurrent droughts. Effects of shrub establishment method enhanced by water harvesting techniques to rehabilitate degraded rangelands have not been well addressed. The main goal of this study was to evaluate the impact of direct seeding and transplanting of seedlings in combination with semi-circular bunds on growth, yield, and survival rate of four shrub species (Atriplex halimus, Atriplex nummularia, Atriplex lentiformis, and Maireana brevifolia) under semi- arid conditions of Sayyad village, Khulm watershed. Survival rate (%), plant height, width, and plant length (cm) and plant cover (%) were measured for each plant over five occasions. A non-destructive reference unit was used to estimate biomass production. The results showed that growth attributes and biomass production of shrubs were consistently greater in the transplanting compared to direct seeding. On average, the plant length, width, height, volume, cover, and biomass production of transplanted shrubs were greater than direct-seeded shrubs by 24.3%, 8.6%, 8.7%, 121.5%, 13.8% and 34.1%, respectively. Biomass production of transplanted seedlings was the highest for A. nummularia (1313.5 g DM/plant) and A. halimus (800 g DM/plant). There was a strong correlation between plant biomass production and plant volume (R2 Plant volume = 0.88) for the shrub A. nummularia, indicating that plant volume is a key variable for assessing biomass production for this species. Additionally, the survival rate of M. brevifolia was 100% in both planting methods, suggesting that based on better survival this halophytic plant has great potential when restoring degraded rangelands

Assessment of soil nutrient balance: approaches and methodologies

Nutrient-balance assessments are valuable tools for delineating the consequences of farming on soil fertility. Various approaches and methods for different situations have been used. This bulletin presents a state-of-the-art overview of nutrient-balance studies. It brings out the evolution of the approaches and methods, provides for comparisons among them, features the improvements made, and highlights remaining issues. The analysis would be useful in further development of the assessment methodologies as reliable tools for devising time-scale soil fertility management interventions