Dynamical Tuning of the Initial Condition for New Inflation in Supergravity

We point out that for a class of `new inflation' models in supergravity the required initial value of the inflaton field is dynamically set if there is another inflation (`pre-inflation') before the `new inflation'. We study the dynamics of both inflatons by taking a hybrid inflation model for the `pre-inflation' as an example. We find out that our `new inflation' model provides reheating temperatures T_R \simeq 10 MeV - 10^4 GeV low enough to avoid the gravitino problem even in gauge-mediated supersymmetry-breaking models. We also construct a model where the scale for the `new inflation' is generated by nonperturbative dynamics of a supersymmetric gauge theory.Comment: 16 pages, late

The changing dynamics of US inflation persistence : a quantile regression approach : [Version 4 September 2012]

We examine both the degree and the structural stability of inflation persis tence at different quantiles of the conditional inflation distribution. Previous research focused exclusively on persistence at the conditional mean of the inflation rate. Economic theory, however, provides various reasons -for example downward wage rigidities or menu costs- to expect higher inflation persistence at the upper than at the lower tail of the conditional inflation distribution. Based on post-war US data we indeed find slower mean reversion in response to positive than to negative shocks. We find robust evidence for a structural break in persistence at all quantiles of the inflation process in the early 1980s. Inflation persistence has decreased and become more homogeneous across quantiles. Persistence at the conditional mean became more informative about the degree of persistence across the entire conditional inflation distribution. While prior to the 1980s inflation was not mean reverting in response to large positive shocks, our evidence strongly suggests that since the end of the Volcker disinflation the unit root can be rejected at every quantile including the upper tail of the conditional inflation distribution

Hybrid inflation followed by modular inflation

Inflationary models with a superheavy scale F-term hybrid inflation followed by an intermediate scale modular inflation are considered. The restrictions on the power spectrum P_R of curvature perturbation and the spectral index n_s from the recent data within the power-law cosmological model with cold dark matter and a cosmological constant can be met provided that the number of e-foldings N_HI* suffered by the pivot scale k_*=0.002/Mpc during hybrid inflation is suitably restricted. The additional e-foldings needed for solving the horizon and flatness problems are generated by modular inflation with a string axion as inflaton. For central values of P_R and n_s, the grand unification scale comes out, in the case of standard hybrid inflation, close to its supersymmetric value M_GUT=2.86 x 10^16 GeV, the relevant coupling constant is relatively large (0.005-0.14), and N_HI* is between 10 and 21.7. In the shifted [smooth] hybrid inflation case, the grand unification scale can be identified with M_GUT for N_HI*=21 [N_HI*=18].Comment: 13 pages including 3 figures, uses ws-ijmpa.cls, minor corrections included, talk given at the CTP Symposium on Supersymmetry at LHC: Theoretical and Experimental Perspectives, British University in Egypt (BUE), Cairo, 11-14 March 2007 (to appear in the proceedings

Identifying Universality in Warm Inflation

Ideas borrowed from renormalization group are applied to warm inflation to characterize the inflationary epoch in terms of flows away from the de Sitter regime. In this framework different models of inflation fall into universality classes. Furthermore, for warm inflation this approach also helps to characterise when inflation can smoothly end into the radiation dominated regime. Warm inflation has a second functional dependence compared to cold inflation due to dissipation, yet despite this feature, it is shown that the universality classes defined for cold inflation can be consistently extended to warm inflation.Comment: 20 pages, 5 figures, 1 appendi

Inflation targeting and inflation persistence

This paper argues that the adoption of an inflation target reduces the persistence of inflation. We develop the theoretical literature on inflation persistence by introducing a Taylor rule for monetary policy into a model of persistence and showing that inflation targets reduce inflation persistence. We investigate changes in the time series properties of inflation in seven countries that introduced inflation targets in the late 1980s or early 1990s. We find that the persistence of inflation is greatly reduced or eliminated following the introduction of inflation targets

The euro and inflation uncertainty in the European Monetary Union

In this paper, we investigate empirically the relationship between inflation and inflation uncertainty in twelve EMU countries. We estimate a time-varying parameter model with a GARCH specification for the conditional volatility of inflation in order to distinguish between short-run (structural and impulse) and steady-state uncertainty. We then introduce a dummy variable to model the policy regime shift which occurred in 1999 with the introduction of the Euro, and its effects on the links between inflation and inflation uncertainty. We find that steady-state inflation has generally remained stable (with the important exception of Germany, where the trend has become positive), steady-state inflation uncertainty and inflation persistence have both increased, and the relationship between inflation and inflation uncertainty has broken down in many countries. These findings cast doubt on the optimistic view taken by the ECB concerning its success in controlling inflation, and suggest the need for improvements in its analytical framework

Axion monodromy inflation with sinusoidal corrections

We study the axion monodromy inflation with a non-perturbatively generated sinusoidal term. The potential form is a mixture between the natural inflation and the axion monodromy inflation potentials. The sinusoidal term is subdominant in the potential, but leaves significant effects on the resultant fluctuation generated during inflation. A larger tensor-to-scalar ratio can be obtained in our model. We study two scenarios, single inflation scenario and the double inflation scenario. In the first scenario, the axion monodromy inflation with a sufficient number of e-fold generates a larger tensor-to-scalar ratio about $0.1 - 0.15$ but also a tiny running of spectral index. In the second scenario of double inflation, axion monodromy inflation is its first stage and, we assume another inflation follows. In this case, our model can realize a larger tensor-to-scalar ratio and a large negative running of spectral index simultaneously.Comment: 12 pages, 3 figures, version accepted for publication in PTEP: References and some comments added, and typos correcte