Inflation Regime Research Articles

Modified hybrid inflation, reheating, and stabilization of the electroweak vacuum

We propose a modification to the standard hybrid inflation model \cite{Linde:1993cn}, that connects a successful hybrid inflation scenario to the standard model Higgs sector, via the electroweak vacuum stability. The proposed model results in an effective inflation potential of a hilltop-type, with both the trans-Planckian and sub-Planckian inflation regimes consistent with the recent Planck/BICEP combined results. Reheating via the inflation sector decays to right-handed neutrinos is considered. An upper bound on the reheating temperature $T_{\rm R} \lsim 2\times 10^{11}~(1\times 10^{13})$ GeV, for large~(small) field inflation, will suppress contributions from one-loop quantum corrections to the inflation potential. This may push the neutrino Yukawa couplings to be ${\cal O}(1)$ and affect the vacuum stability. We show that the couplings of the SM Higgs to the inflation sector can guarantee the electroweak vacuum stability up to the Planck scale. The so-called hybrid Higgs-inflaton model leads to a positive correction for the Higgs quartic coupling at a threshold scale, which is shown to have a very significant effect in stabilizing the electroweak vacuum. We find that even with ${\cal O}(1)$ neutrino Yukawa couplings, threshold corrections leave the SM vacuum stability intact.

New Conservation Law and a Consideration as to When Forming a Cosmological Constant Term: Using Fifth Force for Frequency of BEC “Gravitons” and Cosmological Constant Formed before BEC Gravitons Form

We use scalar fields. The scalar field version which we are using is one from Padmanabhan, and the problem is that the scalar field in the Padmanabhan representation is initially only dependent on time. We also refer to a new assumed conservation law which will give new structure as to inflationary expansion and its immediate aftermath. That of the Hubble “constant” is divided by the “time derivative” of the scalar field in the inflation regime and then a long time afterwards. In doing so, we help define when the cosmological constant may form and what they says about the advent of dark energy.

The Transmission of Supply Shocks in Different Inflation Regimes

The Transmission of Supply Shocks in Different Inflation Regimes

Modified Starobinsky inflation by the R ln (□) R term

In the context of effective theories of gravity, a minimalist bottom-up approach which takes into account 1-loop quantum corrections leads to modifications in the Einstein-Hilbert action through the inclusion of four extra terms: R 2, CκραβCκραβ , R ln (□) R and Cκραβ ln(□) Cκραβ . The first two terms are necessary to guarantee the renormalizability of the gravitational theory, and the last two terms (nonlocal terms) arise from the integration of massless/light matter fields. This work aims to analyze how one of the nonlocal terms, namely R ln(□) R, affects the Starobinsky inflation. We consider the nonlocal term as a small correction to the R 2 term, and we demonstrate that the model behaves like a local model in this context. In addition, we show that the approximate model in the Einstein frame is described by a canonical scalar field minimally coupled to general relativity. Finally, we study the inflationary regime of this model and constrain its free parameters through observations of CMB anisotropies.

Constraining the Barbero-Immirzi parameter from the duration of inflation in loop quantum cosmology

We revisit the predictions for the duration of the inflationary phase after the bounce in loop quantum cosmology. We present our analysis for different classes of inflationary potentials that include the monomial power-law chaotic type of potentials, the Starobinsky and the Higgs-like symmetry breaking potential with different values for the vacuum expectation value. Our setup can easily be extended to other forms of primordial potentials than the ones we have considered. Independently on the details of the contracting phase, if the dynamics starts sufficiently in the far past, the kinetic energy will come to dominate at the bounce, uniquely determining the amplitude of the inflaton at this moment. This will be the initial condition for the further evolution that will provide us with results for the number of e-folds from the bounce to the beginning of the accelerated inflationary regime and the subsequent duration of inflation. We also discuss under which conditions each model considered could lead to observable signatures on the spectrum of the cosmic microwave background or else be excluded for not predicting a sufficient amount of accelerated expansion. A first analysis is performed considering the standard value for the Barbero-Immirzi parameter obtained from black hole entropy calculations. In a second analysis, we consider the possibility of varying the value of this parameter, which is motivated by the fact that the Barbero-Immirzi parameter can be considered a free parameter of the underlying quantum theory in the context of loop quantum gravity. From this analysis, we obtain a lower limit for this parameter by requiring the minimum amount of inflationary expansion that makes the model consistent with the CMB observations. [abridged]

Subcritical regime of hybrid inflation with modular A4 symmetry

We consider a supergravity model that has the modular A4 symmetry and discuss the interplay between the neutrino mixing and inflation. The model contains right- handed neutrinos that have the Majorana masses and additional Yukawa couplings to the waterfall field. In the model an active neutrino is massless and we find that only the inverted hierarchy is allowed and the Majorana phase is predicted to be around ±(120–180)° from the observed neutrino mixing data. In the early universe, one of right-handed sneutrinos plays the role of the inflaton field. Focusing on the subcritical regime of the hybrid inflation that is consistent with the cosmic microwave background data, we analyze the dynamics of the scalar sector and derive an upper bound (1010) GeV on the scale of the Majorana mass.

When is gold an effective hedge against inflation?

Using threshold and piecewise regression models on monthly data (January 1969–March 2021), we examine the asymmetric effects of inflation and the US ten-year Treasury bond interest rate on gold price returns, identifying two distinct regimes. Inter alia, it is found that the responsiveness of gold returns to changes in inflation and interest rate depends on the magnitude of monthly inflation itself. Given the recent multi-trillion-dollar stimulus packages, the US is likely to switch into a ‘high’ inflation regime (as defined by our endogenously determined threshold), leading to gold once again becoming a potent hedge against inflation. The results support the view that when monthly inflation in the US exceeds 0.55%, gold exhibits significant responses to changes in both inflation and the ten-year Treasury interest rate. However, when inflation is moderate or low, gold remains somewhat non-responsive. We thus argue that such asymmetric and size-dependent responses are the main causes of the lack of consensus in the literature regarding the hedging capability of gold.

Financial intermediaries and speculation in the foreign exchange market: the role of monetary policy in Iran’s economy

Given the high fluctuations of the general price level, the importance of investment, and accessing sufficient financial resources, we examine the effects of monetary policy on the nominal (Inflation) and real (Investment) sectors of a developing economy, like Iran, through the channel of the relationship between bank deposits, stock market, and speculation in the foreign exchange market (FEM). For this purpose, due to regime switching in Iran’s economy, the non-linear relation between the variables has been investigated by applying Markov switching models and annual data of 1988–2018. The results show that the financial intermediaries (FIs) have not had a complementary relationship in both bear and bull market and high and low banks deposits regimes. Both FIs have negatively impacted speculation in the FEM in high and low exchange rates difference regimes. The difference between official and unofficial exchange rates negatively impacted the FIs in bear market and low banks deposits regimes; on the contrary, a positive effect in a bull market and high bank deposits. The effects of both FIs on investment have been positive in high and low investment regimes and negative on inflation rates in high and very high inflation regimes. In comparison, the impact of speculation in the FEM has been negative on investment and positive on inflation. Therefore, in the event of the lack of limitations regarding using interest rate (IR) and the policy of exchange rate unification, the central bank would be able to affect the nominal and real sectors of the economy suitably through the channels of the FIs and the FEM.

Multi-field cold and warm inflation and the de Sitter swampland conjectures

We discuss under which conditions multi-field cold and warminflationary models with canonical kinetic energy terms are compatiblewith the swampland conjectures about the emergence of de Sitter solutionsin string theory. We find that under quite general conditions the slow-rollconditions for multi-field cold inflation are at odds with the swamplandconjectures for an arbitrary number of scalar fields driving inflation.However, slow-roll conditions can be reconciled with the swampland conjecturesin the strong dissipative regime of warm inflation.

Testing the neo-fisherian hypothesis in Brazil

We investigate the short- and long-run effects of an increase in the nominal interest rate on price inflation during Brazil’s low and stable inflation regime. We estimate the long-run effect using cointegrating regression methods to deal with endogenous regressors and serially correlated errors. Based on monthly inflation and nominal interest rate from 1994 to 2019, the findings support the neo-Fisher effect. The results suggest that price setters might be learning from the Central Bank policy decisions that guide the future movements of the inflation rate. The endogeneity test revealed that the policy rate is weakly exogenous to the inflation rate. We conclude that, in the long run, a rise in the policy rate tends to produce higher inflation rates, as predicted by the neo-Fisher effect.

Asymmetry in the regimes of inflation and business cycles:the New Keynesian Phillips curve

ABSTRACT Employing a novel instrumental variable method, we provide three findings with the idea of introducing regime switching into the NKPC for Australia, Canada, New Zealand, the United Kingdom and the United States. First, the response of inflation to the driving force is asymmetric in expansion/contraction, and high/low inflation regimes. The switch between regimes changes the inflation dynamics, thus changing the trade-off between stabilizing inflation and the output gap. Second, price stickiness changes in regimes. The price rigidity explains the inflation-output gap and the inflation-law of one price gap relationship across regimes. Third, inflation dynamics are more forward-looking in the expansionary regime. These results yield the implications of targeting deviations from the law of one price for stabilizing inflation and business cycles.

Low Inflation Bends the Phillips Curve around the World

This paper finds strong support for a Phillips curve that becomes nonlinear when inflation is “low”—which our baseline model defines as less than 3 percent. The nonlinear curve is steep when output is above potential (slack is negative) but flat when output is below potential (slack is positive) so that further increases in economic slack have little effect on inflation. This finding is consistent with evidence of downward nominal wage and price rigidity. When inflation is high, the Phillips curve is linear and relatively steep. These results are robust to placing the threshold between the high and low inflation regimes at 2, 3, or 4 percent inflation or for a threshold based on country-specific medians of inflation. In this nonlinear model, international factors play a large role in explaining headline inflation (albeit less so for core inflation), a role that has been increasing since the global financial crisis. These results provide evidence of channels which could boost inflation in the future, even if they were dormant before the Covid pandemic.

Chinese influences on inflation determination in Australia and the ASEAN group: A Markov-switching analysis

China's rapidly growing role in the world economy has been accompanied by rising bilateral trade with Australia and the Association of Southeast Asian Nations (ASEAN group) as well as expanded offshore renminbi (RMB) markets in the region. Using a Markov-switching analysis that allows for variation across stable and volatile domestic inflation regimes, we find evidence of significant inflation transmission from China to Australia and the five larger ASEAN economies. Chinese inflation effects are further confirmed when we incorporate money supply and commodity price effects within a Markov-switching Vector Autoregressive (MSVAR) framework. The importance of allowing for regime change over our sample period is clear and these inflation effects are shown to generally be stronger during periods when domestic inflation is more volatile. These findings on inflation pass-through from China represent a novel extension to a prior literature that has been primarily limited to real economy and trade effects.

The Anatomy of Single-Digit Inflation in the 1960s

Recently, the experience of the 1960s—when the U.S. inflation rate rose rapidly and persistently over a comparatively short period—has been invoked as a cautionary tale for the present. An analysis of this period indicates that the inflation regime that prevailed in the 1960s was different in several key regards from the one that prevailed on the eve of the pandemic. Hence, there are few useable lessons to be drawn from this experience, save that monetary policymaking remains a difficult undertaking.

Lorentz violating inflation and the swampland

The swampland conjectures from String theory have had very interesting implications for cosmology and particularly for Inflation. It has been shown that the single field inflationary models in a GR based cosmology are in unavoidable tensions with these conjectures, while these single field models can still be consistent in certain non-trivial inflationary regimes. So it becomes interesting to see whether there is a way to overcome the issues of the swampland and single field inflation in an essentially GR based cosmology. We show that this can indeed be the case and for this, we consider a certain type of Lorentz violating inflationary scenario. We work out the swampland bounds for Lorentz violating inflationary models after which show that inflationary models which would have had otherwise serious tensions with these conjectures in a usual GR based scenario, can be very tranquil with the criterion in this regime. For this we take examples of Higgs inflation, radion gauge inflation and Spontaenous symmetry breaking inflation and show that the bounds imposed by the swampland on the Lorentz violating parameter can be easily satisfied in these models.

Higher-order extension of Starobinsky inflation: Initial conditions, slow-roll regime, and reheating phase

The most current observational data corroborate the Starobinsky model as one of the strongest candidates in the description of an inflationary regime. Motivated by such success, extensions of the Starobinsky model have been increasingly recurrent in the literature. The theoretical justification for this is well grounded: higher-order gravities arise in high-energy physics in the search for the ultraviolet completeness of general relativity. In this paper, we propose to investigate the inflation due to the extension of the Starobinsky model characterized by the inclusion of the ${R}^{3}$ term. We make a complete analysis of the potential and phase space of the model, where we observe the existence of three regions with distinct dynamics for the scalar field. We can establish restrictive limits for the number of $e$-folds through a study of the reheating and by considering the usual couplings of the standard matter fields and gravity. Thereby, we duly confront our model with the observational data from Planck, BICEP3/Keck, and BAO. Finally, we discuss how the inclusion of the cubic term restricts the initial conditions necessary for the occurrence of a physical inflation.

An Investigation on the Impacts of Fuel Carrier Price on the Consumer Price Inflation in Iran

Introduction: Oil is one of the primary commodities of all countries globally and is, in essence, the energy base of all that we know as transportation. Therefore, price fluctuations of derivatives, especially fuel and oil derivatives, are the policymakers’ main concerns because they can cause serious problems, such as inflation in commodity prices. Objective: The impact of fuel carriers’ prices on the consumer price index remains a subject of debate and research. This paper aims to develop a model to define the inflation regime in Iran and then investigate the impact of gasoline and diesel price on the total inflation rate. Method: In this study, using the central bank time series and available data on energy balance and World Bank data banks, a non-linear distributed online delay regression model is developed to analyze the relationship between fuel price and essential commodity inflation. Results: The results show that there is an impact of gasoline prices on inflation. It does not have much effect in the long term, but diesel can somewhat influence raising prices, which can exacerbate poverty in the community that needs special attention. Conclusion: It was also found that increase in diesel’s price is harmful to the economy because it can stimulate inflation in the long term. However, in the short term, diesel does not cause any significant inflation in the prices. While gasoline prices can have many short-term social effects, this paper suggests that the Iranian government's control of diesel fuel prices prevents long-term inflation and inflation in consumer price rate.

English

After decades of failed developmental efforts, many economies around the world employed the McKinnon-Shaw liberalization thesis to propel the development of their financial systems. Whiles some of these economies had success stories, others had frustrating outcomes. This study examines the financial liberalisation and financial development dynamics considering inflationary effects, in SSA spanning 2000 to 2019. We conducted preliminary tests to ascertain the suitability of the data for the study and then estimated the PVAR model. Impulse response functions and forecast error variance decompositions were obtained from the residuals of the model estimates. The study established a weak, long-run bidirectional relationship between liberalization and financial development, with liberalization accounting for about 0.09% of financial development, while financial development explains about 0.06% of liberalization shocks on average. It takes 3 to 5 years for the impact to manifest after policy implementation. The study further revealed a positive short-run bidirectional relationship between inflation and liberalization, and an inverse short-run bidirectional relationship between inflation and financial development. While inflation explains about 0.87 and 1.79% of liberalization and financial development shocks respectively, liberalization and financial developments respectively explain about 2.62 and 7.41% of inflation shocks on average. It takes 1 to 2 years for the impulse to manifest after policy implementation. We recommend that for financial liberalization policies to succeed, stable inflationary regime and the necessary preconditions for liberalization policies should be in place prior to the implementation of liberalization policies.    Key words: Liberalization, financial development, endogeneity, exogeneity, stochastic trend, impulse response functions (irf), and forecast error variance decomposition (fevd).

Nexus between construction sector and economic indicators for Turkey and European Union evidenced by panel data analysis

PurposeThe research aims to study the regression, cointegration and causality between the construction sector (CS) and the Gross Domestic Product (GDP), considering other variables in the study such as interest rate, taxation, industry sector, investment and Foreign Direct Investment (FDI), which are analyzed through unique panel models. The study was conducted in Turkey and the ten other countries of the European Union (EU) from 1988 to 2019.Design/methodology/approachRegression, cointegration and causality methods were used to investigate the different types of relationships between variables in the models. Data were obtained from official databases and the study contains four main stages, which are explained in detail in the methodology section.FindingsThe study used the analysis methods of regression, cointegration and causality tests and found that the CS and GDP have long-run estimates and the relationship between the two for different countries is negative in a two-way direction. Results are detailed in the analysis section.Research limitations/implicationsNo data were available for the variables before 1988 for most countries, which led to a limited number of observations and issues in statistical analysis methods.Originality/valuePreviously, only input and output tables were used in the analysis. The impact of interest rate, taxation, investment and FDI has not been analyzed. Key variables are very relevant for Turkey, which suffers from chronical inflation and taxation regimes. These show variability with the EU countries for comparative analysis and have not been explored to date, remaining as a major gap for the construction industry. No attempts were made to use regression, cointegration and causality methods with variables. These analysis methods enable an understanding of the differences in variance (heteroscedasticity) and the presence of cross-sectional dependence (CSD), both critical for the reliability of the comparison of data sets and analysis.

Global portraits of nonminimal inflation

We reconsider the dynamical systems approach to analyze inflationary universe in the Jordan frame models of scalar field nonminimally coupled to curvature. The adopted set of variables allows us to clearly distinguish between different asymptotic states in the phase space, including the kinetic and inflationary regimes. Inflation is realized as a heteroclinic trajectory originating either at infinity from a nonhyperbolic asymptotic de Sitter point or from a regular saddle de Sitter point. We also present a comprehensive picture of possible initial conditions leading to sufficient inflationary expansion and show their extent on the phase diagrams. In addition we comment on the slow roll conditions applicable in the Jordan frame and show how they approximate the leading inflationary “attractor solution”. As particular examples we portrait quadratic and quartic potential models and note that increasing the nonminimal coupling diminishes the range of good initial conditions in the quadratic case, but enlarges is in the quartic case.