Capital and macroeconomic instability in a discrete-time model with forward-looking interest rate rules

The authors establish the necessary and sufficient conditions for local real determinacy in a discrete-time production economy with monopolistic competition and a quadratic price adjustment cost under forward-looking policy rules, for the case where capital is in exogenously fixed supply and the case with endogenous capital accumulation. Using these conditions, they show that (i) indeterminacy is more likely to occur with a greater share of payment to capital in value-added production cost; (ii) indeterminacy can be more or less likely to occur with constant capital than with variable capital; (iii) indeterminacy is more likely to occur when prices are modelled as jump variables than as predetermined variables; (iv) indeterminacy is less likely to occur with a greater degree of steady-state monopolistic distortions; and (v) indeterminacy is less likely to occur with a greater degree of price stickiness or with a higher steady-state inflation rate. In contrast to some existing research, the authors' analysis indicates that capital tends to lead to macroeconomic instability by affecting firms' pricing behavior in product markets rather than households' arbitrage activity in asset markets even under forward-looking policy rules.Capital ; Interest rates

Matter loops corrected modified gravity in Palatini formulation

Recently, corrections to the standard Einstein-Hilbert action are proposed to explain the current cosmic acceleration in stead of introducing dark energy. In the Palatini formulation of those modified gravity models, there is an important observation due to Arkani-Hamed: matter loops will give rise to a correction to the modified gravity action proportional to the Ricci scalar of the metric. In the presence of such term, we show that the current forms of modified gravity models in Palatini formulation, specifically, the 1/R gravity and $\ln R$ gravity, will have phantoms. Then we study the possible instabilities due to the presence of phantom fields. We show that the strong instability in the metric formulation of 1/R gravity indicated by Dolgov and Kawasaki will not appear and the decay timescales for the phantom fields may be long enough for the theories to make sense as effective field theory . On the other hand, if we change the sign of the modification terms to eliminate the phantoms, some other inconsistencies will arise for the various versions of the modified gravity models. Finally, we comment on the universal property of the Palatini formulation of the matter loops corrected modified gravity models and its implications.Comment: 11 pages, 1 figures, References adde

Modulation spectra capture EEG responses to speech signals and drive distinct temporal response functions

Speech signals have a unique shape of long-term modulation spectrum that is distinct from environmental noise, music, and non-speech vocalizations. Does the human auditory system adapt to the speech long-term modulation spectrum and efficiently extract critical information from speech signals? To answer this question, we tested whether neural responses to speech signals can be captured by specific modulation spectra of non-speech acoustic stimuli. We generated amplitude modulated (AM) noise with the speech modulation spectrum and 1/f modulation spectra of different exponents to imitate temporal dynamics of different natural sounds. We presented these AM stimuli and a 10-min piece of natural speech to 19 human participants undergoing electroencephalography (EEG) recording. We derived temporal response functions (TRFs) to the AM stimuli of different spectrum shapes and found distinct neural dynamics for each type of TRFs. We then used the TRFs of AM stimuli to predict neural responses to the speech signals, and found that (1) the TRFs of AM modulation spectra of exponents 1, 1.5, and 2 preferably captured EEG responses to speech signals in the δ band and (2) the θ neural band of speech neural responses can be captured by the AM stimuli of an exponent of 0.75. Our results suggest that the human auditory system shows specificity to the long-term modulation spectrum and is equipped with characteristic neural algorithms tailored to extract critical acoustic information from speech signals

Newtonian limit of the singular f(R) gravity in the Palatini formalism

Recently D. Vollick [Phys. Rev. D68, 063510 (2003)] has shown that the inclusion of the 1/R curvature terms in the gravitational action and the use of the Palatini formalism offer an alternative explanation for cosmological acceleration. In this work we show not only that this model of Vollick does not have a good Newtonian limit, but also that any f(R) theory with a pole of order n in R=0 and its second derivative respect to R evaluated at Ro is not zero, where Ro is the scalar curvature of background, does not have a good Newtonian limit.Comment: 9 page

Cosmological Effects of Nonlinear Electrodynamics

It will be shown that a given realization of nonlinear electrodynamics, used as source of Einstein's equations, generates a cosmological model with interesting features, namely a phase of current cosmic acceleration, and the absence of an initial singularity, thus pointing to a way to solve two important problems in cosmology

Primordial Black Hole Formation from Inflaton

Measurements of the distances to SNe Ia have produced strong evidence that the Universe is really accelarating, implying the existence of a nearly uniform component of dark energy with the simplest explanation as a cosmological constant. In this paper a small changing cosmological term is proposed, which is a function of a slow-rolling scalar field, by which the de Sitter primordial black holes' properties, for both charged and uncharged cases, are carefully examined and the relationship between the black hole formation and the energy transfer of the inflaton within this cosmological term is eluciatedComment: 6 pages, Late

Mutant reduction based on dominance relation for weak mutation testing

Context: As a fault-based testing technique, mutation testing is effective at evaluating the quality of existing test suites. However, a large number of mutants result in the high computational cost in mutation testing. As a result, mutant reduction is of great importance to improve the efficiency of mutation testing. Objective: We aim to reduce mutants for weak mutation testing based on the dominance relation between mutant branches. Method: In our method, a new program is formed by inserting mutant branches into the original program. By analyzing the dominance relation between mutant branches in the new program, the non-dominated one is obtained, and the mutant corresponding to the non-dominated mutant branch is the mutant after reduction. Results: The proposed method is applied to test ten benchmark programs and six classes from open-source projects. The experimental results show that our method reduces over 80% mutants on average, which greatly improves the efficiency of mutation testing. Conclusion: We conclude that dominance relation between mutant branches is very important and useful in reducing mutants for mutation testing