1,721,164 research outputs found
Power suppression at large scales in string inflation
No full textWe study a possible origin of the anomalous suppression of the power spectrum at large angular scales in the cosmic microwave background within the framework of explicit string inflationary models where inflation is driven by a closed string modulus parameterizing the size of the extra dimensions. In this class of models the apparent power loss at large scales is caused by the background dynamics which involves a sharp transition from a fast-roll power law phase to a period of Starobinsky-like slow-roll inflation. An interesting feature of this class of string inflationary models is that the number of e-foldings of inflation is inversely proportional to the string coupling to a positive power. Therefore once the string coupling is tuned to small values in order to trust string perturbation theory, enough e-foldings of inflation are automatically obtained without the need of extra tuning. Moreover, in the less tuned cases the sharp transition responsible for the power loss takes place just before the last 50-60 e-foldings of inflation. We illustrate these general claims in the case of Fibre inflation where we study the strength of this transition in terms of the attractor dynamics, finding that it induces a pivot from a blue to a redshifted power spectrum which can explain the apparent large scale power loss. We compute the effects of this pivot for example cases and demonstrate how magnitude and duration of this effect depend on model parameters
Correlation between dark matter and dark radiation in string compactifications
No full textReheating in string compactifications is generically driven by the decay of the lightest modulus which produces Standard Model particles, dark matter and light hidden sector degrees of freedom that behave as dark radiation. This common origin allows us to find an interesting correlation between dark matter and dark radiation. By combining present upper bounds on the effective number of neutrino species Neff with lower bounds on the reheating temperature as a function of the dark matter mass mDM from Fermi data, we obtain strong constraints on the (Neff, mDM)-plane. Most of the allowed region in this plane corresponds to non-thermal scenarios with Higgsino-like dark matter. Thermal dark matter
can be allowed only if Neff tends to its Standard Model value. We show that the above situation is realised in models with perturbative moduli stabilisation where the production of dark radiation is unavoidable since bulk closed string axions remain light and do not get eaten up by anomalous U(1)s
Nonthermal dark matter in string compactifications
Full text linkNonthermal cosmological histories are capable of greatly increasing the available parameter space of different particle physics dark matter (DM) models and are well motivated by the ubiquity of late-decaying gravitationally coupled scalars in UV theories like string theory. A nonthermal DM model is presented in the context of LARGE Volume Scenarios in type IIB string theory. The model is capable of addressing both the moduli-induced gravitino problem as well as the problem of overproduction of axionic dark radiation and/or DM. We show that the right abundance of neutralino DM can be obtained in both thermal under and overproduction cases for DM masses between O(GeV) and O(TeV). In the latter case the contribution of the QCD axion to the relic density is totally negligible, while in the former case it can be comparable to that of the neutralino thus resulting in a multicomponent DM scenario
Just enough inflation: power spectrum modifications at large scales
No full textWe show that models of `just enough' inflation, where the slow-roll evolution lasted only 50- 60 e-foldings, feature modifications of the CMB power spectrum at large angular scales. We perform a systematic analytic analysis in the limit of a sudden transition between any possible non-slow-roll background evolution and the final stage of slow-roll inflation. We find a high degree of universality since most common backgrounds like fast-roll evolution, matter or radiation-dominance give rise to a power loss at large angular scales and a peak together with an oscillatory behaviour at scales around the value of the Hubble parameter at the beginning of slow-roll inflation. Depending on the value of the equation of state parameter, different pre-inflationary epochs lead instead to an enhancement of power at low ℓ, and so seem disfavoured by recent observational hints for a lack of CMB power at ℓlesssim 40. We also comment on the importance of initial conditions and the possibility to have multiple pre-inflationary stages
Exploiting the “Bare Necessities”: Unemployment, Redistribution and Party-System Fragmentation 1
No full textuseful comments and suggestions. Konstantinos Matakos would also like to thank Bhaskar Dutta and Ben Lockwoo
The Political Economy of India’s Fiscal Federal System and its Reform
Full text linkThis article examines recent and potential reforms in India’s fiscal federal system. We summarize key federal institutions in India, including tax and expenditure assignments, and mechanisms for Center-state transfers. We discuss the institutional process by which reforms can and do take place, including the role of academics, political influences, and especially institutions such as the Finance Commission. In contrast to the past, recent commissions have played a greater role in articulating an agenda for fiscal federal reform, which then proceeds through political bargaining. This change has taken place in the context of, and been influenced by, broader economic reform in India.intergovernmental transfers; economic reform; federalism; regional inequalities
Markets with bilateral bargaining and incomplete information
Full text linkWe study the relationship between bargaining and competition with incomplete information. We consider a model with two uninformed and identical buyers and two sellers. One of the sellers has a privately-known reservation price, which can
either be Low or High. The other seller’s reservation price is commonly known to be in between the Low and High values of the privately-informed seller. Buyers move in sequence, and make offers with the second buyer observing the offer
made by the first buyer. The sellers respond simultaneously. We show that there are two types of (perfect Bayes) equilibrium. In one equilibrium, the buyer who moves second does better. In the second equilibrium, buyers’ expected payoffs are equalised, and the price received by the seller with the known reservation value is determined entirely by the equuilibrium of the two-player game between a single buyer and an informed seller. We also discuss extensions of the model to multiple buyers and sellers, and to the case where both sellers are privately informed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Holding India together: The role of institutions of federalism
Full text linkIndia is a large, heterogeneous and complex nation, with multiple languages, religions and ethnicities, and over one billion people. It stands out in having held together while sustaining a working democracy for over five decades, at relatively low levels of income. One of the main institutional aspects of managing heterogeneity to preserve national unity is the structures of Indian federalism. This paper traces some of the features of Indian federal institutions, focusing on their contribution to this ‘holding together.’ It reviews the conceptual and analytical underpinnings of the role of federal structures in sustaining unity, and summarizes historical developments and current institutional structures of the Indian case. It assesses the role of federal dimensions of political, administrative and judicial structures in the holding together function. It also examines fiscal federal institutions and their impacts, including distributional and growth issues. It also separately focuses specifically on the special treatment of what may be characterized as India’s periphery.federalism, decentralization, intergovernmental relations
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