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In fact, the majority of scientific questions asked by biologists could never be formulated or even conceived without reference to some sort of hierarchical arrangement of taxa, making classification the most fundamental of all biological sciences. The majority of biologists might agree that taxonomy's goal should be to identify the components of biodiversity, especially since accurate identification of the organisms is essential for biosecurity and best crop management practices. However, field knowledge in both taxonomy and application is dwindling. As a result, it is critical to identify any pests or other organisms. Since adopting new taxonomic technology in 2011, USDA Animal and Plant Health Inspection Service, Plant Protection and Quarantine (APHIS-PPQ) has created an impressive array of identification tools, many of which are gaining enormous popularity. Indian algorithms have not yet been used to create India's own software or appropriate database for this purpose. We created our own algorithm by using Neuroptera (Insecta) of West Bengal, India as our model organism because it is region-specific database dependent, both for the creation of our own "Digital Key" experiment and for the identification of insects that can control aphids, as bio control agents, we have chosen the predator group of Aphids (Homoptera: Aphididae). As a result, we experimentally created www.lacewingsofwestbengal.in, a web platform, and a "Digital Key" of "Genus" of a chosen Neuropteran group.

From the beginning of the 1980s, the first theoretical analysis of intra-industry trade showed that the determinants and consequences of this type of trade are different, depending on whether the traded products differ in quality. When the products are subject to intra-industry trade between two countries with distinct qualities, this trade is vertically differentiated. Otherwise, it is called horizontal differentiation. There is a method for distinguishing intra-industry trade between two countries in vertical differentiation from those in horizontal differentiation. This method compares exports' unit value to imports for each industry's intra-industry trade. It considers the intra-industry trading carried out in this industry as vertical differentiation when the unit value of exports differs significantly from that of imports. This approach has limitations. The discussion below will lead us to think about an alternative method for separating and measuring intra-industry trade into horizontal and vertical differentiation., 12 pages

The development of research studies concerning the emergence of intra-industry trade is fruitful interaction between theoretical explanations and empirical methods to measure this phenomenon. The foundation of indicators to measure the intensity of intra-industry trading caused the rise of theoretical models explaining the determinants of these trade flows. It also contributed to the debate on the need to distinguish, in empirical analyses, intra-industry trade in horizontal differentiation from that in vertical differentiation.

From a historical perspective, the development of research studies concerning the emergence of intra-industry trade is fruitful interaction between theoretical explanations and empirical methods to measure this phenomenon. The foundation of indicators to measure the intensity of intra-industry trading caused the rise of theoretical models explaining the determinants of these trade flows. It also contributed to the debate on the need to distinguish, in empirical analyses, intra-industry trade in horizontal differentiation from that in vertical differentiation.

This paper deals with the problem of measuring intra-industry trade. In section 2, it presents two existing approaches (Balboni, 2007) to measuring intra-industry trade: the so called “recovery of trade”, developed by Balassa (1966); Grubel and Lloyd (1975) & the “type of trade” one initiated by Abd-el Rahman (1986b); Vona (1991). Then this paper presents indicators and empirical methods inspired by these two approaches. Notions of trade recovery & trade type come from two different definitions of the empirical phenomena they aim to measure. This paper also discusses these definitions and the theoretical foundations in the section 3.

What happens when the most dynamic entrepreneurial businesses in a country are effectively born global, or when most advanced production facilities are owned and operated by foreign firms which turn out products invented elsewhere? Is thin industrialization the result of policy failure, or is it systemic and unavoidable? Can it be unwound by neo-nationalists? What impact does this have on working and middle classes and social development?

Nowadays most of the production processes are composed of different tasks performed by several geographically separated economic agents with its profound impact similar to what observed regarding the division of labour. This system of global production sharing, which is known as Global Value Chains (GVCs), is eventually forming an extensive network of economic values or value added that explains the changing nature of international trade & development. In this context, the gross nature of imports and exports data is such that it cannot provide any direct information about the foreign and domestic value added to an economy. Analysis of value-added trade requires much more sophisticated data like TiVA and WIOD. Nonetheless, we can get some indirect indications about the GVC phenomenon through a set of analytic refinements based on gross trade data and its informed classifications.

The whole purpose of this part of my research is to quantify the degree of value transformation taking place domestically between imports and exports due to India’s GVC integration in the manufacturing sector. The consideration of using gross imports & exports data to draw a quantitative inference about India’s GVC potential leads to a different conceptualisation of the existing production process regarding knowledge, learning, and upgrading. Traditional trade theories assume that the whole production process of a product is taken place in one country and is marketed in another. However, the notion of GVC trade is different – quantifying how much of India’s export value is contributed by imports and how much India is adding value to exports. The basic concept is "import to export" or I2E.

• The conceptualisation of GVC links... Definitions • The structure of GVC links... Trends & Patterns • GVC Link formation mechanisms... Drivers • Shaping economic & social outcomes... Impacts

The statistical challenges of globalization are profound. We cannot rely solely on national statistics to understand how economies work and how to create industrial policies focusing on competitiveness. It is necessary to see the whole. National statistics build pictures based on relationships between producers and consumers and the rest of the world. But these relationships, especially those with the rest of the world, have become increasingly more complex. There is an increasing need to consider global production within a global accounting framework. This implies a departure from the traditional role of international organizations as compilers of internationally comparable national statistics to bring together the national tables to create a global table.

Though the basic (the late 1860s) Marxian model, under the capitalist mode of production, assumes (more or less) perfect competitive or contestable ambience within the market by means of a large number of trivial firms in each industry, Marx was cognizant of the growing size of firms, the subsequent dwindling of competition, and the evolution of monopolistic or anti-competitive power. Hence, the capital has the inclination for concentration and centralization in the hands of the richest and big capitalists. Actually, the concentration and centralization of capital are two capital accumulation (or self-expansion of capital) techniques. Such concentration and centralization of capital can be clearly detected at this modern time, especially in the USA, in the enormous occurrences of mergers, acquisitions and conglomerates. In this assignment, henceforth, I will be trying to cultivate an analytical discussion about these two interlinked concepts and their implications and repercussions in this modern world of capitalism.

International audience; The global production as a system of creating values is eventually forming a vast web of value chains. It explains the transitional structures of world trade and development of the world economy. It is truly a new wave of globalisation, and we term it as the global value chains (GVCs), creating the nexus among firms, workers and consumers around the globe. The emergence of this new scenario raises some crucial questions. It asks how an economy's businesses, producers and employees are connecting to the global economy. How are they capturing the gains out of it regarding different dimensions of economic development? Indeed, this GVC approach is very crucial for understanding the organisation of the global industries and firms. It requires analysing the statics and dynamics of different economic players involved in this complex global production network. Its widespread notion deals with diverse global, regional, and local issues from the top-down to bottom-up, building scope for policy analysis. In this context, this study will attempt to quantify the extent and impacts of India's engagement in GVCs, based on available data. It will also strive to propose a comprehensive strategic framework to identify the objectives of India's GVC participation and development with some suitable economic strategies to achieve them.

Part I: Stylised facts of Global Value Chains (GVCs) Concept – Structure – Formation – Impacts Part II: Modeling Learning & Upgrading in Global Value Chains (GVCs) Motivation – Fundamentals – Conceptualisation – Structuralisation – Formation – Impacts

International audience; As we can understand with the spread of GVCs, a lot of new questions emerge regarding the measurement of participation and positioning in the globalised production process. The World Development Report (WDR) 2020 explains the GVC phenomenon and then focus on participation and the prospects especially in a world of change in technology. From the overview section, we can figure out that nowadays, goods and services flow across borders as intermediate inputs rather than final goods. In traditional trade, we need two countries with the notions of export and import. However, in GVC trade, the goods and services cross borders multiple times requiring more than two countries. Remarkable improvements in information, communication, and transport technologies have made it possible to fragment production across national boundaries. So the question is: how to conceptualise this type of new trade to justify the measurement of participation.

International audience; Purpose of this background note is to present some relevant research issues about India's GVC, such as degree of India's GVC linkages, by sector, by industry (preliminary analysis by GVC measures as well as in-depth econometric analysis), consequences of GVCs for economic prosperity i.e. industrial or economic upgrading (including trade-oriented upgrading and adaptation), the impact of GVCs on social upgrading, such as reflection on labour market dynamics (because social upgrading is not immediately associated with industrial or economics upgrading).

International audience; The phenomenon of global value chains (GVCs) indicates a division of labour type production structure in which tasks and business functions are distributed among several companies, globally, or regionally (Grossman and Rossi-Hansberg 2008). The critical features of GVCs are therefore the international dimension of the production process and the "contractualisation" of buyer and seller relationships, often across international borders (Antras 2016). As a result, these international production networks are highly complex regarding geography, technology, and the different types of firms involved (from large retailers and highly large-scale mechanised manufacturers to small home-based production). Sometimes it may be impossible even to identify all the countries that are involved or the extent of their involvement (Gereffi and Fernandez-Stark 2016). However, the recent development of OECD-WTO's Trade-in Value Added (TiVA) data represents a fundamental step forward in understanding GVC trade. Grossman & Rossi-Hansberg (2008, 2012) rightly point out that the different tasks, rather than sectors, define the specialisation of countries in the value chains.

Comment: 15 pages, The global production (as a system of creating values) is eventually forming a vast web of value chains that explains the transitional structures of global trade and development of the world economy. It is truly a new wave of globalisation, and we can term it as the global value chains (GVCs), creating the nexus among firms, workers and consumers around the globe. The emergence of this new scenario is asking how an economy's businesses, producers and employees are connecting to the global economy and capturing the gains out of it regarding different dimensions of economic development. Indeed, this GVC approach is very crucial for understanding the organisation of the global industries (including firms) through analysing the statics and dynamics of different economic players involved in this complex global production network. Its widespread notion deals with various global issues (including regional value chains also) from the top down to the bottom up, founding a scope for policy analysis.

The topic of my research is "Learning and Upgrading in Global Value Chains: An Analysis of India's Manufacturing Sector". To analyse India's learning and upgrading through position, functions, specialisation & value addition of manufacturing GVCs, it is required to quantify the extent, drivers, and impacts of India's Manufacturing links in GVCs. I have transformed this overall broad objective into three fundamental questions: (1) What is the extent of India's Manufacturing Links in GVCs? (2) What are the determinants of India's Manufacturing Links in GVCs? (3) What are the impacts of India's Manufacturing Links in GVCs? These three objectives represent my three chapters in my PhD thesis., 26 pages, PhD Proposal

International audience; Indeed, the global production (as a system of creating values) is eventually forming like a gigantic and complex network/web of value chains that explains the transitional structures of global trade and development of the global economy. It’s truly a new wave of globalisation, and we term it as the global value chains (GVCs), creating the nexus among firms, workers and consumers around the globe. The emergence of this new scenario asks– how an economy’s firms, producers and workers connect in the global economy. And how are they capturing the gains out of it in terms of different dimensions of economic development? This GVC approach is very crucial for understanding the organisation of the global industries and firms. It requires the statics and dynamics of diverse players involved in this complex global production network. Its broad notion deals with different global issues (including regional value chains also) from the top down to the bottom up, founding a scope for policy analysis (Gereffi & Fernandez-Stark 2011). But it is true that as Feenstra (1998) points out, any single computational framework is not sufficient to quantification this whole range of economic activities. We should adopt an integrative framework for accurate projection of this dynamic multidimensional phenomenon.

The importance of trade to an economy needs no emphasis. You sell products or services that you are competitive at and buy those where you are not. Experience of countries such as South Korea and China demonstrate that resources required for development can be garnered through trade; thus, motivating many countries to embrace trade as a means for development. Simultaneously, emergence of 'Global Value Chain' or 'GVC' as they are popularly known has changed the way we trade. Though the concept of GVC was introduced in the early 2000s, there are examples of global value chains before the 1980s. However, the scale of the phenomenon and the way in which technological change, by lowering trade costs, has allowed fragmentation of production was not possible before (Hernandez et al., 2014). In this context, the World Bank has recently published its 'World Development Report 2020: Trading for Development in the Age of Global Value Chains' (WDR). The report prescribes that GVCs still offer developing countries a clear path to progress and that developing countries can achieve better outcomes by pursuing market-oriented reforms specific to their stage of development. This commentary is the outcome of a panel discussion held at CDS on January 17, 2020. We are grateful to Prof. Sunil Mani, Prof. Sudip Chaudhuri and other participants at the panel discussion for their comments which has benefited this commentary. We are solely responsible for any errors that remain.

We investigate cosmological scenarios of generalized Chaplygin gas in a universe governed by Horava-Lifshitz gravity. We consider both the detailed and non-detailed balance versions of the gravitational background, and we include the baryonic matter and radiation sectors. We use observational data from Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), and Cosmic Microwave Background (CMB), along with requirements of Big Bang Nucleosynthesis (BBN), to constrain the parameters of the model, and we provide the corresponding likelihood contours. We deduce that the present scenario is compatible with observations. Additionally, examining the evolution of the total equation-of-state parameter, we find in a unified way the succession of the radiation, matter, and dark energy epochs, consistently with the thermal history of the universe., Comment: 16 pages, 14 figures, version published in Gen.Rel.Grav

We reexamine the evolution of thermal relic particle abundances for the case where the interaction rate depends on the particle velocities. For the case of Sommerfeld enhancement, we show that the standard analytic approximation, modified in a straightforward way, provides an estimate of the relic particle abundance that is accurate to within 10% (in comparison to less than 1% error for the non-Sommerfeld-enhanced case). We examine the effect of kinetic decoupling on relic particle abundances when the interaction rate depends on the velocity. For the case of pure p-wave annihilation, the effect of kinetic decoupling is an increase in the relic abundance, but the effect is negligible when the kinetic decoupling temperature is much less than the chemical decoupling temperature. For the case of Sommerfeld-enhanced s-wave annihilations, after kinetic decoupling occurs, annihilations continue to change the particle abundance down to arbitrarily low temperatures, until either matter domination begins or the Sommerfeld effect cuts off. We derive analytic approximations to give the final relic particle abundances for both of these cases., 6 pages, 5 figures. Discussion and clarification added. To appear in Phys. Lett. B.

We examine dark energy models in which a phantom field $\phi$ is rolling near a local minimum of its potential $V(\phi)$.We require that $(1/V)(dV/d\phi) \ll 1$, but $(1/V)(d^2 V/d\phi^2)$ can be large. Using techniques developed in the context of hilltop quintessence, we derive a general expression for $w$ as a function of the scale factor, and as in the hilltop case, we find that the dynamics of the field depend on the value of $(1/V)(d^2 V/d\phi^2)$ near the mimimum. Our general result gives a value for $w$ that is within 1% of the true (numerically-derived) value for all of the particular cases examined. Our expression for $w(a)$ reduces to the previously-derived phantom slow-roll result of Sen and Scherrer in the limit where the potential is flat, $(1/V)(dV/d\phi) \ll 1$., Comment: v3: Discussion modified in accordance with referee comments. References added. Results and Conclusions unchanged. v2: Minor typo corrected in Eqn. 16. Results and Conclusions unchanged

International audience; Slowdown of industrial growth, particularly since the late sixties, had attracted a great deal of scholarly attention in India. That ongoing scholarly discussions created a debate which was in marked contrast to the relative consensus that prevailed in the professional economic circles in the sixties. Many explanations had been offered to solve this debate. Those explanations, some mutually reinforcing, others mutually conflicting, have highlighted the following set of factors: poor agricultural performance despite the Green Revolution. relative price movements resulting in a shift in terms of trade against industry, unequal income distribution and resulting lack of demand, slowdown in import substitution, declining levels of public investment and increasing inefficiencies in the industrial structure resulting from governmental controls and policies. Now the obvious questions are: Why this incommensurability? How far do the available explanations account for the slow industrial growth? Are there other alternative explanations? On what yardsticks can we say that there has been a slowdown? Is the slowdown after 1965-66 a secular or cyclical process’? What does it mean for future policy’? In this review I will try to answer these fundamental questions through analytical reasoning of different articles.

International audience; The crucial and growing role performed by different financial intermediaries such as venture capitalists and angel investors as well as more traditional intermediaries such as commercial banks in developing entrepreneurial or innovative firms and boosting product market innovations has led to great research interest in the economics of innovation and entrepreneurial finance. Besides this, there are some important factors or developments which have affected the entrepreneurial finance in general as well as its influence upon different entrepreneurial or innovative firms. Indeed, it is also true that the financial and ownership structures of the different entrepreneurial firms and the legal as well as institutional environment, in which they operate, itself affects the product market innovations (Chemmanur and Fulghieri, 2014). .Therefore, in this paper I want to target a broad theme i.e. analysis of the mechanisms behind this scenario, especially, in the context of Indian market system.

We perform a combined perturbation and observational investigation of the scenario of non-minimal derivative coupling between a scalar field and curvature. First we extract the necessary condition that ensures the absence of instabilities, which is fulfilled more sufficiently for smaller coupling values. Then using Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), and Cosmic Microwave Background (CMB) observations, we show that, contrary to its significant effects on inflation, the non-minimal derivative coupling term has a negligible effect on the universe acceleration, since it is driven solely by the usual scalar-field potential. Therefore, the scenario can provide a unified picture of early and late time cosmology, with the non-minimal derivative coupling term responsible for inflation, and the usual potential responsible for late-time acceleration. Additionally, the fact that the necessary coupling term does not need to be large, improves the model behavior against instabilities., Comment: 26 pages, 2 figures, minor changes, version published at JCAP

We investigate the cosmic evolution of the linear bias in the framework of a flat FLRW spacetime. We consider metric perturbations in the Newtonian gauge, including Hubble scale effects. Making the following assumptions, (i) scale independent current epoch bias $b_0$, (ii) equal accelerations between tracers and matter, (iii) unimportant halo merging effects (which is quite accurate for $z, Comment: 11 pages, 3 figures, accepted for publication in Phys. Rev. D

We examine the evolution of quintessence models with potentials satisfying (V'/V)^2<, 6 pages, 5 figures, references added

We show that the f(T) gravitational paradigm, in which gravity is described by an arbitrary function of the torsion scalar, can provide a mechanism for realizing bouncing cosmologies, thereby avoiding the Big Bang singularity. After constructing the simplest version of an f(T) matter bounce, we investigate the scalar and tensor modes of cosmological perturbations. Our results show that metric perturbations in the scalar sector lead to a background-dependent sound speed, which is a distinguishable feature from Einstein gravity. Additionally, we obtain a scale-invariant primordial power spectrum, which is consistent with cosmological observations, but suffers from the problem of a large tensor-to-scalar ratio. However, this can be avoided by introducing extra fields, such as a matter bounce curvaton., 10 pages, 3 figures

We investigate the cosmological perturbations in f(T) gravity. Examining the pure gravitational perturbations in the scalar sector using a diagonal vierbien, we extract the corresponding dispersion relation, which provides a constraint on the f(T) ansatzes that lead to a theory free of instabilities. Additionally, upon inclusion of the matter perturbations, we derive the fully perturbed equations of motion, and we study the growth of matter overdensities. We show that f(T) gravity with f(T) constant coincides with General Relativity, both at the background as well as at the first-order perturbation level. Applying our formalism to the power-law model we find that on large subhorizon scales (O(100 Mpc) or larger), the evolution of matter overdensity will differ from LCDM cosmology. Finally, examining the linear perturbations of the vector and tensor sectors, we find that (for the standard choice of vierbein) f(T) gravity is free of massive gravitons., Comment: 11 pages, 4 figures. Analysis of the vector and tensor sectors added

Models that lead to a cosmological stiff fluid component, with a density $\rho_S$ that scales as $a^{-6}$, where $a$ is the scale factor, have been proposed recently in a variety of contexts. We calculate numerically the effect of such a stiff fluid on the primordial element abundances. Because the stiff fluid energy density decreases with the scale factor more rapidly than radiation, it produces a relatively larger change in the primordial helium-4 abundance than in the other element abundances, relative to the changes produced by an additional radiation component. We show that the helium-4 abundance varies linearly with the density of the stiff fluid at a fixed fiducial temperature. Taking $\rho_{S10}$ and $\rho_{R10}$ to be the stiff fluid energy density and the standard density in relativistic particles, respectively, at $T = 10$ MeV, we find that the change in the primordial helium abundance is well-fit by $\Delta Y_p = 0.00024(\rho_{S10}/\rho_{R10})$. The changes in the helium-4 abundance produced by additional radiation or by a stiff fluid are identical when these two components have equal density at a "pivot temperature", $T_*$, where we find $T_* = 0.55$ MeV. Current estimates of the primordial $^4$He abundance give the constraint on a stiff fluid energy density of $\rho_{S10}/\rho_{R10} < 30$., Comment: 6 pages, 2 figures. Clarification added: element abundances derived using a full numerical calculation. Version accepted at PRD

A $\Lambda$CDM model with dark matter that decays into inert relativistic energy on a timescale longer than the Hubble time will produce an expansion history that can be misinterpreted as stable dark matter with time-varying dark energy. We calculate the corresponding spurious equation of state parameter, $\widetilde w_\phi$, as a function of redshift, and show that the evolution of $\widetilde w_\phi$ depends strongly on the assumed value of the dark matter density, erroneously taken to scale as $a^{-3}$. Depending on the latter, one can obtain models that mimic quintessence ($\widetilde w_\phi > -1$), phantom models ($\widetilde w_\phi < -1$) or models in which the equation of state parameter crosses the phantom divide, evolving from $\widetilde w_\phi > -1$ at high redshift to $\widetilde w_\phi < -1$ at low redshift. All of these models generically converge toward $\widetilde w_\phi \approx -1$ at the present. The degeneracy between the $\Lambda$CDM model with decaying dark matter and the corresponding spurious quintessence model is broken by the growth of density perturbations., Comment: 6 pages, 2 figures. Added discussion of linear perturbation growth - version accepted at PRD

We propose a class of simple dark energy models which predict a late-time dark radiation component and a distinctive time-dependent equation of state $w(z)$ for redshift $z < 3$. The dark energy field can be coupled strongly enough to Standard Model particles to be detected in colliders, and the model requires only modest additional particle content and little or no fine-tuning other than a new energy scale of order milli-electron volts., 12 pages, 4 figures. Selected for Honorable Mention in the 2010 Gravity Research Foundation Essay awards

We propose a scale dependent analytic approximation to the exact linear growth of density perturbations in Scalar-Tensor (ST) cosmologies. In particular, we show that on large subhorizon scales, in the Newtonian gauge, the usual scale independent subhorizon growth equation does not describe the growth of perturbations accurately, as a result of scale-dependent relativistic corrections to the Poisson equation. A comparison with exact linear numerical analysis indicates that our approximation is a significant improvement over the standard subhorizon scale independent result on large subhorizon scales. A comparison with the corresponding results in the Synchronous gauge demonstrates the validity and consistency of our analysis., 10 pages, 5 figures. Minor modifications and references added to match published version

We use observational data from Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), and Cosmic Microwave Background (CMB), along with requirements of Big Bang Nucleosynthesis (BBN), to constrain the running parameter $\lambda$ of Horava-Lifshitz gravity, which determines the flow between the Ultra-Violet and the Infra-Red. We consider both the detailed and non-detailed balance versions of the gravitational sector, and we include the matter and radiation sectors. Allowing for variation of all the parameters of the theory, we construct the likelihood contours and we conclude that in $1\sigma$ confidence $\lambda$ is restricted to $|\lambda-1|\lesssim0.02$, while its best fit value is $|\lambda_{b.f}-1|\approx0.002$. Although this observational analysis restricts the running parameter $\lambda$ very close to its IR value 1, it does not enlighten the discussion about the theory's possible conceptual and theoretical problems., Comment: 9 pages, 2 figures, version published at JCAP

We investigate f(T) cosmology in both the background, as well as in the perturbation level, and we present the general formalism for reconstructing the equivalent one-parameter family of f(T) models for any given dynamical dark energy scenario. Despite the completely indistinguishable background behavior, the perturbations break this degeneracy and the growth histories of all these models differ from one another. As an application we reconstruct the f(T) equivalent for quintessence, and we show that the deviation of the matter overdensity evolution is strong for small scales and weak for large scales, while it is negligible for large redshifts., Comment: 11 pages, 12 figures, version published at JCAP

We use observational data from Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), and Cosmic Microwave Background (CMB), along with requirements of Big Bang Nucleosynthesis (BBN), to constrain the cosmological scenarios governed by Horava-Lifshitz gravity. We consider both the detailed and non-detailed balance versions of the gravitational sector, and we include the matter and radiation sectors. We conclude that the detailed-balance scenario cannot be ruled out from the observational point of view, however the corresponding likelihood contours impose tight constraints on the involved parameters. The scenario beyond detailed balance is compatible with observational data, and we present the corresponding stringent constraints and contour-plots of the parameters. Although this analysis indicates that Horava-Lifshitz cosmology can be compatible with observations, it does not enlighten the discussion about its possible conceptual and theoretical problems., 11 pages, 6 figures, version published in JCAP

We demonstrate the scale dependence of the growth function of cosmological perturbations in dark energy models based on General Relativity. This scale dependence is more prominent on cosmological scales of $100h^{-1}Mpc$ or larger. We derive a new scale dependent parametrization which generalizes the well known Newtonian approximation result $f_0(a)\equiv \frac{d\ln \delta_0}{d\ln a}=\om(a)^\gamma$ ($\gamma ={6/11}$ for \lcdm) which is a good approximation on scales less than $50h^{-1}Mpc$. Our generalized parametrization is of the form $f(a)=\frac{f_0(a)}{1+\xi(a,k)}$ where $\xi(a,k)=\frac{3 H_{0}^{2} \omm}{a k^2}$. We demonstrate that this parametrization fits the exact result of a full general relativistic evaluation of the growth function up to horizon scales for both \lcdm and dynamical dark energy. In contrast, the scale independent parametrization does not provide a good fit on scales beyond 5% of the horizon scale ($k\simeq 0.01 h^{-1}Mpc$)., Comment: Revised and extended version. No changes in results. 7 pages, 4 figures. The mathematica files used for the production of the figures may be downloaded from http://leandros.physics.uoi.gr/newpar.zip

We examine dark energy models in which a quintessence or a phantom field, $\phi$, rolls near the vicinity of a local minimum or maximum, respectively, of its potential $V(\phi)$. Under the approximation that $(1/V)(dV/d\phi) \ll 1$, [although $(1/V)(d^2 V/d\phi^2)$ can be large], we derive a general expression for the equation of state parameter $w$ as a function of the scale factor for these models. The dynamics of the field depends on the value of $(1/V)(d^2 V/d\phi^2)$ near the extremum, which describes the potential curvature. For quintessence models, when $(1/V)(d^2 V/d\phi^2)3/4$, $w(a)$ has oscillatory behavior. For phantom fields, the dividing line between these two types of behavior is at $(1/V)(d^2 V/d\phi^2) = -3/4$. Our analytical expressions agree within 1% with the exact (numerically-derived) behavior, for all of the particular cases examined, for both quintessence and phantom fields. We present observational constraints on these models., Comment: 8 pages, 10 figures

The effect of quintessence perturbations on the integrated Sachs-Wolfe (ISW) effect is studied for a mixed dynamical scalar field dark energy (DDE) and pressureless perfect fluid dark matter. A new and general methodology is developed to track the growth of the perturbations, which uses only the equation of state (EoS) parameter w{sub DDE}(z){identical_to}p{sub DDE}/{rho}{sub DDE} of the scalar field DDE, and the initial values of the relative entropy perturbation (between the matter and DDE) and the intrinsic entropy perturbation of the scalar field DDE as inputs. We also derive a relation between the rest-frame sound speed c-circumflex{sub s,DDE}{sup 2} of an arbitrary scalar field DDE component and its EoS w{sub DDE}(z). We show that the ISW signal differs from that expected in a {lambda}CDM cosmology by as much as +20% to -80% for parametrizations of w{sub DDE} consistent with SNIa data, and about {+-}20% for parametrizations of w{sub DDE} consistent with SNIa+CMB+BAO data, at 95% confidence. Our results indicate that, at least in principle, the ISW effect can be used to phenomenologically distinguish a cosmological constant from DDE.

We propose a simple dark energy model with the following properties: the model predicts a late-time dark radiation component that is not ruled out by current observational data, but which produces a distinctive time-dependent equation of state w(z) for z < 3. The dark energy field can be coupled strongly enough to Standard Model particles to be detected in colliders, and the model requires only modest additional particle content and little or no fine-tuning other than a new energy scale of order milli-electron volts., 6 pages, 5 figures, revtex; v2: footnote 3 added, minor changes, published version

We derive slow-roll conditions for thawing k-essence with a separable Lagrangian $p(X,\phi)=F(X)V(\phi)$. We examine the evolution of the equation of state parameter, $w$, as a function of the scale factor $a$, for the case where $w$ is close to -1. We find two distinct cases, corresponding to $X \approx 0$ and $F_X \approx 0$, respectively. For the case where $X\approx0$ the evolution of $\phi$ and hence $w$ is described by only two parameters, and $w(a)$ is model-independent and coincides with similar behavior seen in thawing quintessence models. This result also extends to non-separable Lagrangians where $X\approx0$. For the case $F_X \approx 0$, an expression is derived for $w(a)$, but this expression depends on the potential $V(\phi)$, so there is no model-independent limiting behavior. For the $X \approx 0$ case, we derive observational constraints on the two parameters of the model, $w_0$ (the present-day value of $w$), and the $K$, which parametrizes the curvature of the potential. We find that the observations sharply constrain $w_0$ to be close to -1, but provide very poor constraints on $K$., Comment: 7 pages and 5 figures, typos corrected

We examine a dark energy model where a scalar unparticle degree of freedom plays the role of quintessence. In particular, we study a model where the unparticle degree of freedom has a standard kinetic term and a simple mass potential, the evolution is slowly rolling and the field value is of the order of the unparticle energy scale ($\lambda_u$). We study how the evolution of $w$ depends on the parameters $B$ (a function of the unparticle scaling dimension $d_u$), the initial value of the field $\phi_i$ (or equivalently, $\lambda_u$) and the present matter density $\Omega_{m0}$. We use observational data from Type Ia supernovae, BAO and CMB to constrain the model parameters and find that these models are not ruled out by the observational data. From a theoretical point of view, an unparticle dark energy model is very attractive, since unparticles (being bound states of fundamental fermions) are protected from radiative corrections. Further, coupling of unparticles to the standard model fields can be arbitrarily suppressed by raising the fundamental energy scale $M_F$, making the unparticle dark energy model free of most of the problems that plague conventional scalar field quintessence models., Comment: v1: 7 pages, 8 figures, version accepted by Phys.Rev.D V2: refs added, matches PRD version

Oscillating scalar fields, with an oscillation frequency much greater than the expansion rate, have been proposed as models for dark energy. We examine these models, with particular emphasis on the evolution of the ratio of the oscillation frequency to the expansion rate. We show that this ratio always increases with time if the dark energy density declines less rapidly than the background energy density. This allows us to classify oscillating dark energy models in terms of the epoch at which the oscillation frequency exceeds the expansion rate, which is effectively the time at which rapid oscillations begin. There are three basic types of behavior: early oscillation models, in which oscillations begin during the matter-dominated era, late oscillation models, in which oscillations begin after scalar-field domination, and non-oscillating models. We examine a representative set of models (those with power-law potentials) and determine the parameter range giving acceptable agreement with the supernova observations. We show that a subset of all three classes of models can be consistent with the observational data., Comment: 6 pages, 7 figures, references and brief discussion added, matches version to appear in Phys. Rev. D

We study the creation of solitons from particles, using the $\lambda \phi^4$ model as a prototype. We consider the scattering of small, identical, wave pulses, that are equivalent to a sequence of particles, and find that kink-antikink pairs are created for a large region in parameter space. We also find that scattering at {\it low} velocities is favorable for creating solitons that have large energy compared to the mass of a particle., Comment: 4 pages, 2 figures. Animations at http://www.hep.vanderbilt.edu/~duttas/kkbar.html .Included acknowledgments and fixed (minor) typos. Clarifying remarks added. Version accepted for PRL

We examine hilltop quintessence models, in which the scalar field is rolling near a local maximum in the potential, and w is close to -1. We first derive a general equation for the evolution of the scalar field in the limit where w is close to -1. We solve this equation for the case of hilltop quintessence to derive w as a function of the scale factor; these solutions depend on the curvature of the potential near its maximum. Our general result is in excellent agreement (delta w < 0.5%) with all of the particular cases examined. It works particularly well (delta w < 0.1%) for the pseudo-Nambu-Goldstone Boson potential. Our expression for w(a) reduces to the previously-derived slow-roll result of Sen and Scherrer in the limit where the curvature goes to zero. Except for this limiting case, w(a) is poorly fit by linear evolution in a., 7 pages, 9 figures, label on Fig. 4 corrected

We examine the accuracy of the growth equation $\ddot{\delta} + 2H\dot{\delta} - 4\pi G\rho\delta = 0$, which is ubiquitous in the cosmological literature, in the context of the Newtonian gauge. By comparing the growth predicted by this equation to a numerical solution of the linearized Einstein equations in the $\Lambda$CDM scenario, we show that while this equation is a reliable approximation on small scales ($k\gtrsim $h Mpc$^{-1}$), it can be disastrously inaccurate ($\sim 10^4% $) on larger scales in this gauge. We propose a modified version of the growth equation for the Newtonian gauge, which while preserving the simplicity of the original equation, provides considerably more accurate results. We examine the implications of the failure of the growth equation on a few recent studies, aimed at discriminating general relativity from modified gravity, which use this equation as a starting point. We show that while the results of these studies are valid on small scales, they are not reliable on large scales or high redshifts, if one works in the Newtonian gauge. Finally, we discuss the growth equation in the synchronous gauge and show that the corrections to the Poisson equation are exactly equivalent to the difference between the overdensities in the synchronous and Newtonian gauges., Comment: Added refs and further discussion of gauge issues. Results and conclusions unchanged. Version accepted at PRD

We investigate the clustering properties of a dynamical dark energy component. In a cosmic mix of a pressureless fluid and a light scalar field, we follow the linear evolution of spherical matter perturbations. We find that the scalar field tends to form underdensities in response to the gravitationally collapsing matter. We thoroughly investigate these voids for a variety of initial conditions, explain the physics behind their formation and consider possible observational implications. Detection of dark energy voids will clearly rule out the cosmological constant as the main source of the present acceleration., 9 pages, 13 figures V3: typo in equation (11) corrected

Computing the perturbation spectrum in the recently proposed Island Cosmology remains an open problem. In this paper we present a classical computation of the perturbations generated in this scenario by assuming that the NEC-violating field behaves as a classical phantom field. Using an exactly-solvable potential, we show that the model generates a scale-invariant spectrum of scalar perturbations, as well as a scale-invariant spectrum of gravitational waves. The scalar perturbations can have sufficient amplitude to seed cosmological structure, while the gravitational waves have a vastly diminished amplitude., 8 pages, 1 figure