Standard Inflation Research Articles

How Rare Is Rare? How Common Is Common? Empirical Issues Associated With Binary Dependent Variables With Rare Or Common Event Rates

The use of logit and probit models when examining binary dependent variables including those in the form 0/1 (i.e., dummy variables), yes/no, and true/false (hereafter binary DVs) is commonplace. Yet, the appropriateness and effectiveness of such models are challenged when the event rate of a binary DV is rare or common. To better understand the impact on the field of strategy, we undertook a literature review and assessed recently published research in the Strategic Management Journal. We then utilized Monte Carlo simulations with results showing that as event rates become rarer or more common, issues including biased coefficients, standard error inflation, low statistical power to detect significant effects, and model convergence failure increasingly arise. In addition, small sample sizes amplified these empirical issues. Using a strategy example study, we also show how various analytic tools can lead to different findings when empirical models face an extreme event rate with small sample sizes. Based on our findings, we provide step-by-step guidance for strategy researchers going forward.

On Robustness of Average Inflation Targeting

This paper considers the performance of average inflation targeting (AIT) policy in a New Keynesian model with adaptive learning agents. Our analysis raises concerns regarding robustness of AIT when agents have imperfect knowledge. In particular, the target steady state can be locally unstable under learning if details about the policy are not publicly available. Near the low steady state with interest rates at the zero lower bound, AIT does not necessarily outperform a standard inflation targeting policy. Policymakers can improve outcomes under AIT by (i) targeting a discounted average of inflation, or (ii) communicating the data window for the target.

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.

On the Trans-Planckian Censorship Conjecture and the generalized non-minimal coupling

We investigate the Trans-Planckian Censorship Conjecture (TCC) and the arising bounds on the inflationary cosmology caused by that conjecture. In that investigation, we analyze TCC bounds for both Jordan and Einstein frames in the presence of a generic non-minimal coupling (to gravity) term. That term allows us to use the functional freedom it brings to the inflationary Lagrangian as an effective Planck mass. In this sense, we argue one should consider the initial field value of the effective Planck mass for the TCC. We show that as a result, one can remove the TCC upper bounds without the need to produce a new process or go beyond the standard inflation mechanism, with the generalized non-minimal coupling, and for Higgs-like symmetry-breaking potentials.

Worry and rumination predict insomnia in patients with coronary heart disease: a cross-sectional study with long-term follow-up.

Insomnia is highly prevalent and associated with anxiety and depression in patients with coronary heart disease patients. The development of effective psychological interventions is needed. Worry and rumination are potential risk factors for the maintenance of insomnia, anxiety, and depression that may be modified by psychological treatment grounded in the Self-Regulatory Executive Function model. However, the relationships between worry, rumination, anxiety and depression, and insomnia are not known. Therefore, we investigated these relationships both cross-sectionally and longitudinally among patients with coronary heart disease. A cross-sectional study consecutively included 1,082 patients in 2014-2015, and 686 were followed up after mean of 4.7 years. Data were gathered from hospital records and self-report questionnaires comprising assessment of worry (Penn State Worry Questionnaire), rumination (Ruminative Responses Scale), anxiety and depression (Hospital Anxiety and Depression Scale), and insomnia (Bergen Insomnia Scale). Insomnia correlated moderately with all other psychological variables (R 0.18-0.50, all P values < .001). After adjustments for anxiety and depression, odds ratios for insomnia at baseline were 1.27 (95% confidence interval 1.08-1.50) and 1.60 (95% confidence interval 1.31-1.94) per 10 points increase of worry and rumination, respectively. Corresponding odds ratios for insomnia at follow-up were 1.28 (95% confidence interval 1.05-1.55) and 1.38 (95% confidence interval 1.09-1.75). Depression was no longer significantly associated with insomnia after adjustments for worry and rumination, but anxiety remained significant. Worry and rumination predicted insomnia both cross-sectionally and prospectively, even after controlling for anxiety and depression, although anxiety remained significant. Future studies may test psychological interventions targeting these factors in patients with coronary heart disease and insomnia. Frøjd LA, Papageorgiou C, Munkhaugen J, etal. Worry and rumination predict insomnia in patients with coronary heart disease: a cross-sectional study with long-term follow-up. J Clin Sleep Med. 2022;18(3):779-787.

Precision cosmology and the stiff-amplified gravitational-wave background from inflation: NANOGrav, Advanced LIGO-Virgo and the Hubble tension

The recent NANOGrav finding of a common-spectrum process has invited interpretationsas possible evidence of a primordial stochastic gravitational-wave background (SGWB)stronger than predicted by standard inflation + ΛCDM.Such an SGWB would contribute an extra radiation component to the background Universe which may affect its expansion history. As such, it may help alleviate the current Hubble tension, a novel connection between gravitational waves and cosmology.We demonstrate this by considering a cosmological model, the “standard inflation + stiff amplification” scenario,with two components added to the base-ΛCDM model: a stiff component (w ≡ p/ρ = 1) and the primordial SGWB.Previously, we showed that even for standard inflation,the SGWB may be detectable at the high frequencies probed by laser interferometers,if it is amplified by a possible early stiff era after reheating.Models that boost the SGWB enough to cause significant backreaction, however,must still preserve the well-measured radiation-matter equality, respecting the demands of precision cosmology.For that, we calculate the fully-coupled evolution of the SGWB and expansion history,sampling parameter space (tensor-to-scalar ratio, reheating temperature and temperature at stiff-to-radiation equality).We then perform a joint analysis of the NANOGrav results and latest upper bounds from Planck,big bang nucleosynthesis and Advanced LIGO-Virgo, to constrain the model.The resulting blue-tilted, stiff-amplified SGWB is still too small to explain the NANOGrav results.However, if someday, Advanced LIGO-Virgo detects the SGWB,our model can explain it within standard inflation (without requiring an initial spectral tilt).Meanwhile, this model may bring current high-z measurements of the Hubble constantwithin 3.4σ of the low-z measurements by SH0ES (from 4.4σ)and within 2.6σ of those by H0LiCOW (from 3.1σ), reducing the tension.

Realistic inflation in no-scale U(1) R symmetric flipped SU(5)

We have realized non-minimal Higgs inflation and standard hybrid inflation in the supersymmetric flipped SU(5) model with U(1) R symmetry using the no-scale form of the Kähler potential. In non-minimal Higgs inflation the waterfall Higgs field plays the role of inflaton, and in standard hybrid inflation the gauge singlet field S is employed as an inflaton. The predictions of both models are in good agreement with the Planck 2018 data. For numerical calculations we have fixed the gauge symmetry breaking scale, M, around 2 × 1016 GeV. In both models the inflaton field values are constrained below mP . The tensor to scalar ratio r in non-minimal inflation is of the order of 10-3 and for standard hybrid inflation r is tiny, of order 10-15–10-4. The scalar spectral index in both cases lie within the Planck 1-σ bounds, and the running of the scalar spectral index lies in the range, -dns /d ln k ∼ 6 × 10-4 for non-minimal model and 10-9–10-3 for the standard hybrid model. A realistic scenario of reheating and non-thermal leptogenesis is employed with reheat temperature Tr ∼ 109 GeV for non-minimal model and 106–1010 GeV for standard hybrid model. The R-symmetry plays a vital role in forbidding rapid proton decay, but at the same time it also suppresses terms responsible for generating right handed neutrino masses. A realistic scenario of right handed neutrino masses is obtained by considering effective R symmetry breaking at the nonrenormalizable level with adequate suppression of rapid proton decay.

Anisotropic hyperbolic inflation

Hyperbolic inflation is an extension of the slow-roll inflation in multi-field models. We extend hyperbolic inflation by adding a gauge field and find four-type attractor solutions: slow-roll inflation, hyperbolic inflation, anisotropic slow roll inflation, and anisotropic hyperbolic inflation. We perform the stability analysis with the dynamical system method. We also study the transition behaviors of solutions between anisotropic slow roll inflation and anisotropic hyperbolic inflation. Our result indicates that destabilization of the standard slow-roll inflation ubiquitously occurs in multi-scalar-gauge field inflationary scenarios.

Geometry near the inner horizon of a rotating, accreting black hole

Here we present a novel classical model to describe the near-inner horizon geometry of a rotating, accreting black hole. The model assumes spacetime is homogeneous and is sourced by radial streams of a collisionless, null fluid, and it predicts that the standard Poisson-Israel mass inflation phenomenon will be interrupted by a Kasner-like collapse toward a spacelike singularity. Thus, the inner horizon and any additional structure beyond it never gets a chance to form. Such a model is shown to be valid near the inner horizon of astrophysically realistic black holes through comparison to the conformally separable Kerr model, which provides a natural connection of the Kerr metric to a self-similar, accreting spacetime. We then analyze the behavior of null geodesics in our model, connecting them to the Kerr metric in order to answer the practical question of what an infalling observer approaching the inner horizon might see. We find that an infalling zero-energy observer near the inner horizon will initially see streams of matter accelerating at high energies along the radial direction. Then, within a short span of proper time, the geometry will enter a collapse phase as most of the background sky becomes squashed along the edge of the black hole's shadow. Classically, the observer's journey will end here at a spacelike singularity, though the final outcome of the collapse will require a future calculation of the quantum back reaction within this framework.

Determinacy and E-Stability with Interest Rate Rules at the Zero Lower Bound

We evaluate and compare alternative monetary policy rules, namely average inflation targeting, price level targeting, and traditional inflation targeting rules, in a standard New Keynesian model that features recurring, transient zero lower bound regimes. We use determinacy and expectational stability (E-stability) of equilibrium as the criteria for stabilization policy. We find that price level targeting policy, including nominal income targeting as a special case, most effectively promotes determinacy and E-stability among the policy frameworks, whereas standard inflation targeting rules are prone to indeterminacy. Average inflation targeting can induce determinacy and E-stability effectively, provided the averaging window is sufficiently long.

Determinacy and E-stability with Interest Rate Rules at the Zero Lower Bound

This paper examines the uniqueness and learnability of rational expectations equilibrium when the policy rate is occasionally pegged at the zero lower bound (ZLB). We consider a model that features recurring, transient ZLB regimes and compare various interest rate rules which respond to inflation, price level, and average inflation in addition to output. In this environment, determinacy conditions ensure a unique equilibrium, given the recurrence of ZLB events, and E-stability conditions can rule out deflationary spirals under learning. We fi nd that price level targeting, including nominal income targeting as a special case, most effectively promotes determinacy and E-stability among the policy frameworks, while the economy under a standard inflation targeting rule is prone to indeterminacy. Average inflation targeting can promote determinacy and E-stability very effectively, provided that the measure of average inflation is sufficiently backward looking.

On Robustness of Average Inflation Targeting

This paper considers the performance of average inflation targeting (AIT) policy in a New Keynesian model with adaptive learning agents. Our analysis raises concerns regarding robustness of AIT when agents have imperfect knowledge. In particular, the target steady state can be locally unstable under learning if details about the policy are not publicly available. Near the low steady state with interest rates at the zero lower bound, AIT does not necessarily outperform a standard inflation targeting policy. Policymakers can improve outcomes under AIT by (i) targeting a discounted average of inflation, or (ii) communicating the data window for the target.

Optimal Monetary Policy with the Risk-Taking Channel

Empirical research suggests that lower interest rates induce banks to take higher risks. We assess analytically what this risk-taking channel implies for optimal monetary policy in a tractable New Keynesian model. We show that this channel creates a motive for the planner to stabilize the real rate. This objective conflicts with the standard inflation stabilization objective. Optimal policy thus tolerates more inflation volatility. An inertial Taylor-type reaction function becomes optimal. We then quantify the significance of the risk-taking channel for monetary policy in an estimated medium-scale extension of the model. Ignoring the channel when designing policy entails non-negligible welfare costs (0.7% lifetime consumption equivalent).

Price level versus inflation targeting under heterogeneous expectations: a laboratory experiment

Abstract Since the 2007 crisis, macroeconomists have been interested in monetary policies that could help with stabilizing inflation and output (Honkapohja, 2015). Two ideas gained particular attention: (i) that inflation should be replaced by the nominal price level (PLT) as the target for the central bank; and (ii) that the central bank should provide explicit guidance about its interest rate rule. We conduct a laboratory experiment to test the validity of these two hypotheses. Our experiment uses a Learning-to-Forecast design based on a simple DSGE economy. Subjects are given a qualitative description of the economy and are asked to predict inflation and output gap two-periods ahead for 50 periods. There are five treatments. Baseline treatment (1) incorporates a standard inflation targeting rule. The other four treatments utilize a PLT Taylor rule and are based on a two-by-two design: a ‘weak’ PLT rule (2) with guidance and (3) without guidance; and a ‘strong’ PLT rule (4) with guidance and (5) without guidance. By guidance we mean that the central bank informs subjects about the price level deviation from its target. We find that subjects within each treatment coordinate on similar behavior, but large differences between the treatments prevail. Guidance has a negligible effect, whereas a weak or strong Taylor rule specification turns out to be crucial for stability. PLT can be a robust monetary policy, but only if it is sufficiently responsive to the deviations of output and prices.

Open versus endovascular REBOA control of blood loss during cesarean delivery in the placenta accreta spectrum: A single-center retrospective case control study

ObjectiveThe aim of this study was to compare two vascular control options for blood loss prevention and hysterectomy during cesarean delivery (CD22Cesarean delivery.): endovascular balloon occlusion of the aorta (REBOA33Resuscitative endovascular balloon occlusion of the aorta.) and open bilateral common iliac artery occlusion (CIAO44Common iliac artery occlusion.) in women with extensive placenta accreta spectrum (PAS55Placenta accreta spectrum.). Study designThis was retrospective comparison of cases of PAS using either CIAO (October 2017 through October 2018) or REBOA (November 2018 through November 2019) to prevent pathologic hemorrhage during scheduled CD. Women with confirmed placenta increta/percreta underwent either CD then intraoperative post-delivery, pre-hysterectomy open vascular control of both CIA66Common iliac artery. (CIAO group) or pre-operative, ultrasound-guided, fluoroscopy-free REBOA followed by standard CD and balloon inflation after fetal delivery (REBOA group). Intraoperative blood loss, transfusion volumes, surgical time, blood pressure, maternal and neonatal outcomes, hospitalization length and postoperative complications were compared. ResultsThe REBOA and CIAO groups included 12 and 16 women, respectively, with similar median age of 35 years and gestational age of 34–35 weeks. All REBOA catheters were successfully placed into aortic zone three under ultrasound guidance. The quantitated median intraoperative blood loss was significantly lower for the REBOA group, (541 [IQR 300–750] mL) compared to the CIAO group (3331 [IQR 1150−4750] mL (P = 0.001). As a result, the total volume of fluid and blood replacement therapy was significantly lower in the REBOA group (P < 0.05). Median surgical time in the REBOA group was less than half as long: 76 [IQR 64−89] minutes compared to 168 [IQR 90−222] minutes in the CIAO group (P = 0.001). None of the women with REBOA required hysterectomy, while 8/16 women in the CIAO group did (P = 0.008). Furthermore, the post-anesthesia recovery and hospital discharge times in the REBOA-group were shorter (P < 0.05). One thromboembolic complication occurred in each group. The only REBOA-associated complication was non-occlusive femoral artery thrombosis, with no surgical management required. No maternal or neonatal deaths occurred in either group. ConclusionFluoroscopy-free REBOA for women with PAS is associated with improved vascular control, perioperative blood loss, the need for transfusion and hysterectomy and reduces surgical time when compared to bilateral CIAO.

Effect of brane tension on reheating parameters in small field inflation according to Planck-2018 data

We study a new reheating approach in the framework of standard and braneworld inflation. Using the technique developed in Ref. 1, we consider a small field arctangent potential and show that this approach can be similarly applied within Randall–Sundrum type 2 scenario and provide additional constraints to reheating temperature [Formula: see text] and duration of reheating [Formula: see text]. We found that in brane case the effective equation-of-state parameter [Formula: see text] must be close to 1, to satisfy Planck-2018 joint constraints on [Formula: see text].

Palatini-Higgs inflation with nonminimal derivative coupling

The predictions of standard Higgs inflation in the framework of the metric formalism yield a tensor-to-scalar ratio $r\ensuremath{\sim}{10}^{\ensuremath{-}3}$ which lies well within the expected accuracy of near-future experiments $\ensuremath{\sim}{10}^{\ensuremath{-}4}$. When the Palatini formalism is employed, the predicted values of $r$ get highly suppressed $r\ensuremath{\sim}{10}^{\ensuremath{-}12}$ and consequently a possible nondetection of primordial tensor fluctuations will rule out only the metric variant of the model. On the other hand, the extremely small values predicted for $r$ by the Palatini approach constitute contact with observations a hopeless task for the foreseeable future. In this work, we propose a way to remedy this issue by extending the action with the inclusion of a generalized nonminimal derivative coupling term between the inflaton and the Einstein tensor of the form ${m}^{\ensuremath{-}2}(\ensuremath{\phi}){G}_{\ensuremath{\mu}\ensuremath{\nu}}{\ensuremath{\nabla}}^{\ensuremath{\mu}}\ensuremath{\phi}{\ensuremath{\nabla}}^{\ensuremath{\nu}}\ensuremath{\phi}$. We find that with such a modification, the Palatini predictions can become comparable with the ones obtained in the metric formalism, thus providing ample room for the model to be in contact with observations in the near future.

Higgs inflation, vacuum stability, and leptogenesis

We consider the introduction of a complex scalar field carrying a global lepton number charge to the Standard Model and the Higgs inflation framework. The conditions are investigated under which this model can simultaneously ensure Higgs vacuum stability up to the Planck scale, successful inflation, non-thermal Leptogenesis via the pendulum mechanism, and light neutrino masses. These can be simultaneously achieved when the scalar lepton is minimally coupled to gravity, that is, when standard Higgs inflation and reheating proceed without the interference of the additional scalar degrees of freedom. If the scalar lepton also has a non-minimal coupling to gravity, a multi-field inflation scenario is induced, with interesting interplay between the successful inflation constraints and those from vacuum stability and Leptogenesis. The parameter region that can simultaneously achieve the above goals is explored.

Inflation with a class of concave inflaton potentials in Randall\u2013Sundrum model

We investigate inflation with a class of concave inflaton potentials of the form sim phi ^n(0<n<1) in the Randall–Sundrum model with an infinite extra spatial dimension. We show that this class of models is much more in good agreement with observations compared to the standard inflation. We also find the range of the five-dimensional Planck scale (M_5) and show that large tensor-to-scalar ratios do not eliminate small-field inflation in braneworld cosmology.

A solution to the initial condition problems of inflation: NATON

The recent astonishing realization of the negative absolute temperature (NAT) for motional degrees of freedom \cite{Braun_ea13} inspires its possible application to the early universe. The existence of the upper bound on the energy of the system is the sufficient requirement for a NAT and this might correspond to the Planck scale at the Big Bang model. It has been argued that standard inflation requires an initial patch that is smooth over distance scales a bit larger than the causal horizon at the onset of inflation. We show that this initial condition problem can be solved if the NAT fermion, dubbed ``NATON'', occupies the Universe before the standard inflation is ignited by providing mini inflation prior to the standard one. As long as NATON dominated era lasts until at least ten times older than the Planck time, it makes the Universe homogeneous enough to derive the successful standard inflation.