Theory Of Inflation Research Articles

Analysis of gravitational waves from inflation model with minimal, non-minimal, and non-minimal derivative coupling of scalar field from Horndeski theory

Inflation theory provides solutions for problems in cosmology, such as horizon problem and flatness problem. The study of Gravitational waves production in cosmic inflation era not prove the general inflation theory, but also to differentiate in detail among specific models. In this research, we use inflation model with minimal, non-minimal, and non-minimal derivative coupling of scalar field without potential from Horndeski Theory. From this model, we calculate scalar and tensor perturbation equations and then obtain its equation of gravitational waves, spectral index for each perturbation mode and tensor-to-scalar ratio. Spectral index and tensor-to-scalar ratio nearly scale-invariant and agree with observational data for some Ho, ζ, and ξ. Gravitational waves remain constant during inflation and start oscillates when its modes enter the horizon. Energy of this gravitational waves is scale-invariant for modes that re-enter horizon during radiation dominated era and rises toward lower frequencies.

Possible signature of entanglement in null-energy-condition-violating inflation

In recent years, the classical version of the null energy condition (NEC) has been enhanced into its quantum generalization, the quantum null energy condition (QNEC). The right-hand side of the QNEC inequality is non-zero; it is multiplied by a factor of ћ and recovers the standard NEC in the classical limit. Moreover, the second derivative of entanglement entropy also plays a role in determining the right-hand side. In this work, we study several examples of theories of inflation that violate the standard NEC, yet still, possibly obey the QNEC. This suggests that the deviation of the standard NEC arises due to the existence of entanglement between regions inside and outside of the cosmological horizon. Possible connection to quantum fluctuations of de Sitter spacetime is also studied.

Inflation with Einstein-Gauss-Bonnet, non-minimal, and non-minimal derivative couplings: the constant-roll condition

In our research, we consider and study the inflation theories of Einstein-Gauss-Bonnet, minimal, non-minimal, and non-minimal derivative coupling with the constant-roll condition. Given the gravitational wave event, GW170817, which produces the speed of gravitational waves that was almost equal to the speed of light in vacuum, we constrain that the speed of the tensor perturbation was nearly equal to unity, . We involve a scalar field potential whose function can be obtained from an equation of motion by choosing the Gauss-Bonnet coupling functions. We use the linear and quadratic coupling functions, which are their simplest functions. The one result obtained are able to produce observed quantities such as the spectral index for scalar perturbation, ns = 0.9642, the spectral index for tensor perturbation, nT = −5.2471 × 10−4, and tensor-scalar ratio, r = 0.0041, which are compatible with the newest Planck data using the slow-roll parameters obtained analytically.

Quantum Fluctuations in Vacuum Energy: Cosmic Inflation as a Dynamical Phase Transition

A variety of models of inflation in the early Universe have been proposed and applied to describe successfully the origin of all possible structures in the Universe. On the other hand, inflation theory is still phenomenological and needs systematic physical foundations, including the relation to dark matter and dark energy. The essence of cosmic inflation would be a dynamical phase transition and the spontaneous symmetry breaking process, which are common in ordinary physics in the laboratory. At the beginning of the phase transition, the system is often in an adiabatic ground state and produces a squeezed state. This is widely interpreted as the generation of classical structures; however, it is not. The common notion of decoherence is not sufficient to describe the inflationary phase transition: a particular trajectory must be singled out in the dynamics. When an interaction turns on, dissipation or the energy flow/cascade is possible, and the c-number random field appears. The separation of these classical statistical fluctuations from the deterministic time evolution is indicated by the secular divergence or the infrared divergence of the system. We describe this phase transition based on the closed-time-path method and derive a quantum Langevin equation with classical noise, which sources the development of a coherent state. Introducing the effective action method to describe the evolution of the coherent state, we describe the order parameter that characterizes the phase transition and the associated spontaneous symmetry breaking. Since this phase transition process is common in physics, we discuss further applications of this formalism in other physical systems.

Bootstrapping large graviton non-Gaussianities

Gravitational interferometers and cosmological observations of the cosmic microwave background offer us the prospect to probe the laws of gravity in the primordial universe. To study and interpret these datasets we need to know the possible graviton non-Gaussianities. To this end, we derive the most general tree-level three-point functions (bispectra) for a massless graviton to all orders in derivatives, assuming scale invariance. Instead of working with explicit Lagrangians, we take a bootstrap approach and obtain our results using the recently derived constraints from unitarity, locality and the choice of vacuum. Since we make no assumptions about de Sitter boosts, our results capture the phenomenology of large classes of models such as the effective field theory of inflation and solid inflation. We present formulae for the infinite number of parity-even bispectra. Remarkably, for parity-odd bispectra, we show that unitarity allows for only a handful of possible shapes: three for graviton-graviton-graviton, three for scalar-graviton-graviton and one for scalar-scalar-graviton, which we bootstrap explicitly. These parity-odd non-Gaussianities can be large, for example in solid inflation, and therefore constitute a concrete and well-motivated target for future observations.

Perspectives in cosmology

The “new standard cosmology,” based on the theory of inflation, has very impressive observational support. I review some outstanding problems of the new cosmology and the global view of the universe—the multiverse—that it suggests.

Anisotropy of phase transition gravitational wave and its implication for primordial seeds of the Universe

We quantitatively study how the primordial density fluctuations are imprinted on the anisotropy of the phase transition gravitational wave (PTGW). Generated long before recombination and free from Silk damping, the anisotropic PTGW might reveal the density perturbation seeded from inflation or alternatives. We find new behaviors of the PTGW anisotropy power spectrum. The PTGW anisotropy is stronger than the anisotropy of the cosmic microwave background temperature at all scales, and the high-$\ell$ multiples are enhanced about 1 order due to the early integrated Sachs-Wolfe effect. Furthermore, differences in primordial power spectra at small scales manifest themselves more significantly on the angular power spectrum of PTGW anisotropy compared to that of the cosmic microwave background. These properties might provide a novel clue to understanding the primordial density perturbation of our early Universe and thereby complete our understanding of inflation theory. Taking nanohertz PTGW from dark matter models as a typical example, we obtain amplitudes of PTGW anisotropy which are about 4 or 3 orders weaker than the isotropic PTGW energy spectra.

A differential representation of cosmological wavefunctions

Our understanding of quantum field theory rests largely on explicit and controlled calculations in perturbation theory. Because of this, much recent effort has been devoted to improve our grasp of perturbative techniques on cosmological spacetimes. While scattering amplitudes in flat space at tree level are obtained from simple algebraic operations, things are harder for cosmological observables. Indeed, computing cosmological correlation functions or the associated wavefunction coefficients requires evaluating a growing number of nested time integrals already at tree level, which is computationally challenging. Here, we present a new “differential” representation of the perturbative cosmological wavefunction in de Sitter spacetime that obviates this problem for a large class of phenomenologically relevant theories. Given any tree-level Feynman-Witten diagram, we give simple algebraic rules to write down a seed function and a differential operator that transforms it into the desired wavefunction coefficient for any scale-invariant, parity-invariant theory of massless scalars and gravitons with general boost-breaking interactions. In particular, this applies to large classes of phenomenologically relevant theories such as those described by the effective field theory of inflation or solid inflation. Trading nested bulk time integrals for derivatives on boundary kinematical data provides a great computational advantage, especially for processes involving many vertices.

Regionalized liquidity: A cross-country analysis of mobile money deployment and inflation in developing economies

• Village-level shocks induce the use of mobile money as a risk-sharing instrument across different regions. • Cross-village risk sharing via mobile money systematically reallocates money supply, facilitating inflation. • Increased use of mobile money in response to village-level shocks elevates national consumer price indices. • The power to distribute is equal to the power to generate money supply in countries with limited market integration. Mobile money has been hailed as a serious innovation in the pursuit of financial inclusion and poverty alleviation; however, its macroeconomic effect is not fully understood. This study presents a regional theory of inflation and argues that limited market integration contributes to mobile money’s inflationary effects. Household survey data from Kenya confirms increased use of mobile money after village- and supra-village-level shocks due to risk-sharing between liquidity-flexible and liquidity-constrained regions. A difference-in-differences empirical assessment indicates that mobile money deployment increases national consumer price indices. Findings support that the power to distribute equals the power to generate money supply in developing countries.

Unified model for inflation, pseudo-Goldstone dark matter, neutrino mass, and baryogenesis

We present a unified theory of inflation, neutrino mass, baryogenesis, and dark matter where global lepton number symmetry and its breaking play a crucial role. The basic idea is to use a lepton number carrying a complex scalar field as the inflaton as well as the field that implements Affleck-Dine (AD) leptogenesis. Dark matter is the massive Majoron which is a pseudo-Goldstone boson, resulting from the spontaneous breaking of lepton number symmetry supplemented by explicit lepton number violation needed to implement AD leptogenesis. The magnitude of the resulting ${n}_{B}/s$ in the model is related to the mass of the pseudo-Goldstone dark matter, connecting two apparently disconnected cosmological observations. An inverse seesaw mechanism with lepton number breaking at low scale is crucial to prevent washout of the lepton asymmetry during the universe's evolution. The model seems to provide an economical solution to several puzzles of the standard model of particle physics and cosmology in one stroke.

Credential Inflation and Decredentialization: Re-examining the Mechanism of the Devaluation of Degrees

Abstract Sociologists have long used credential inflation theory to explain the devaluation of tertiary education degrees as the consequence of the excessive supply of educated personnel. However, the literature has inadequately examined two fundamental conditions: the combination of degrees/skills that individuals possess and the level of degrees. In this article, cross-country multilevel regressions reveal lower-level degrees (i.e. short-cycle tertiary) are devalued due to the larger extent of lower-level tertiary expansion in a society, regardless of degree holders’ skills level. This is consistent with the concept of credential inflation. In contrast, alongside the proliferation of higher-level tertiary education (i.e. bachelor and above), individuals with such degrees are penalized only when they lack high skills. Put differently, higher-level degree holders retain their rewards despite their diminishing scarcity as long as they possess high skills. Meanwhile, high skills unaccompanied by tertiary degrees lose their premium merely in connection with lower-level tertiary expansion. These results suggest credentialism is intensified and credential inflation operates in societies where the extent of lower-level tertiary expansion is relatively large, whereas ‘decredentialization’ emerges along with the larger extent of higher-level tertiary expansion in a way that devalues credentials as such whilst relatively enhancing the role of skills in reward allocation.

Monetary policy in a world of radical uncertainty

Monetary policy in a world of radical uncertainty

Minsky’s Theory of Inflation and its Theoretical and Empirical Relevance to Credit-Driven Economies

This article examines Minsky’s theory of inflation, as distinct from a monetary theory of inflation and a productivity-adjusted wage theory of inflation. Minsky’s view on money and banking will be elucidated in contrast to orthodox banking theories, drawing a causal relation from bank credit creation to aggregate demand, profits, and inflation. This article claims that his theory is particularly relevant to modern economies in which the globalization of the production process and the decline in the power of unions have mitigated wage-led inflation while financialization has amplified the business cycle and the movement in inflation over the previous forty years. In other words, excessive bank lending has underpinned aggregate spending, which created too much “claim” on consumer goods, thus precipitating profit-led inflation. By contrast, an unavoidable financial crisis and attempts, especially by households to pay off outstanding debt, dampened aggregate demand, thus causing a slowdown in profits and inflation.

Endogenous income distribution and aggregate demand: Empirical evidence from heterogeneous panel structural vector autoregression

AbstractThis paper presents a novel empirical investigation into demand and distribution dynamics using a heterogeneous panel structural vector autoregression model for a panel of 10 emerging economies during the 1970–2017 period. Following the Kaleckian tradition, the theoretical analysis is based on a dynamic macro model where distributive shares and labor productivity are determined endogenously by introducing conflicting‐claims theory of inflation and Kaldor–Verdoorn effects. The paper indicates profit‐led demand regime only in the short run and profit‐squeeze effects when allowing for the contemporaneous effect of labor share on capacity utilization and capital accumulation. However, after incorporating the contemporaneous effect of demand on labor share and thus controlling for the short‐term effect of pro‐cyclical labor productivity on labor share, the results provide evidence for wage‐led demand and wage‐squeeze effects. These results underline how the importance of addressing endogeneity issues when estimating demand and distribution regimes and how different assumptions about the interactions among demand, distribution, and labor productivity result in diverse findings.

Large power spectrum and primordial black holes in the effective theory of inflation

We study the generation of a large power spectrum, necessary for primordial black hole formation, within the effective theory of single-field inflation. The mechanisms we consider include a transition into a ghost-inflation-like phase and scenarios where an exponentially growing mode is temporarily turned on. In the cases we discuss, the enhancement in the power spectrum results from either a swift change in some effective coupling or a modification of the dispersion relation for the perturbations, while the background evolution remains unchanged and approximately de Sitter throughout inflation. The robustness of the results is guaranteed thanks to a weakly broken galileon symmetry, which protects the effective couplings against large quantum corrections. We discuss how the enhancement of the power spectrum is related to the energy scale of the operators with weakly broken galileon invariance, and study the limits imposed by strong coupling and the validity of the perturbative expansion.

A Fiscal Theory of Persistent Inflation

A Fiscal Theory of Persistent Inflation

Non-Gaussianities in the extended EFT of inflation

In earlier works, we studied the validity of Extended Effective Field Theory of Inflation (EEFToI) in the regime where initial conditions are set with dispersion relations ω 2 ∝ k 6. We had also evaluated and examined the power spectrum for some interesting corners of the parameter space. In this paper, we compute the bispectrum in the EEFToI, take a closer look at the strong coupling constraints and calculate the size of the non-Gaussianities in those regions of parameter space. We also investigate the shape of triangles that contribute to the enhancement of non-Gaussianities in this regime. We find that there are allowed parts of parameter spaces where EEFToI description with initial conditions set with ω 2 ∝ k 6 is sensible and interesting.

Impact of Inflation on The Economic Development of Malaysia

This paper analyses inflation determinants in Malaysia, employing economic indicators. The research expands analytical work on inflation theory determinants in three respects. Second, it looks at a much larger variety of economic variables, all of which are empirically evaluated in various countries. Third, given the different analytical consequences of the economic indicators for each region, the author analyses those precisely concerning inflation determinants based on Malaysian economic performance over the past 43 years, from 1971 to 2013. Besides, more than five literature reviews to identify economic success and inflation are used to do this study. Finally, the third goal of the research is to distinguish inflation causes between different and dependent variables through the Multiple Regression Process. A basic reason for finding a long-term approach is to obtain information about inflation determinants in Malaysia. However, it was not limitable as a proxy for money supplies in Malaysia for high monetary growth (annual percentages). In addition, it is also comprised of macro economically inflation uncertainties, energy, foreign exchange; Imports, and the gross domestic product for goods and services.

The Impacts of Government Spending and Monetary Policy Rate in Indonesia

This study reviews the impacts of government policies on the economy. The period of analysis starts from early banking sector reform until the current Covid-19 pandemic crisis. We apply Vector Error Correction Model based on the theory of money demand and inflation to analyze the relationships among income, inflation, money balance, government spending, and policy interest rate. The impacts of money balance and policy interest rate on income are as predicted by money demand. Financial sector growth and different expectation on inflation affect the efficacy of monetary policy. On the other hand, government spending might not be fully growth-enhancing. The need emerges to classify and distinguish the classes of government spending which increase growth.

Lattice simulations of inflation

The scalar field theory of cosmological inflation constitutes nowadays one of the preferred scenarios for the physics of the early universe. In this paper we aim at studying the inflationary universe making use of a numerical lattice simulation. Various lattice codes have been written in the last decades and have been extensively used for understating the reheating phase of the universe, but they have never been used to study the inflationary phase itself far from the end of inflation (i.e. about 50 e-folds before the end of inflation). In this paper we use a lattice simulation to reproduce the well-known results of some simple models of single-field inflation, particularly for the scalar field perturbation. The main model that we consider is the standard slow-roll inflation with an harmonic potential for the inflaton field. We explore the technical aspects that need to be accounted for in order to reproduce with precision the nearly scale invariant power spectrum of inflaton perturbations. We also consider the case of a step potential, and show that the simulation is able to correctly reproduce the oscillatory features in the power spectrum of this model. Even if a lattice simulation is not needed in these cases, that are well within the regime of validity of linear perturbation theory, this sets the basis to future work on using lattice simulations to study more complicated models of inflation.