Onset Of Inflation Research Articles

Fine-tuning solution for hybrid inflation in dissipative chaotic dynamics

We study the presence of chaotic behavior in phase space in the preinflationary stage of hybrid inflation models. This is closely related to the problem of initial conditions associated with these inflationary types of model. We then show how an expected dissipative dynamics of fields just before the onset of inflation can solve or ease considerably the problem of initial conditions, driving the system naturally toward inflation. The chaotic behavior of the corresponding dynamical system is studied by computation of the fractal dimension of the boundary in phase space separating inflationary from noninflationary trajectories. The fractal dimension for this boundary is determined as a function of the dissipation coefficients appearing in the effective equations of motion for the fields.

Affleck–Dine leptogenesis via right-handed sneutrino fields in a supersymmetric hybrid inflation model

The onset of inflation in hybrid models require fine tuning in the initial conditions. The inflaton field should have an initial value close to the Planck scale $M_{P}$, whereas the auxiliary "orthogonal" field must be close to zero with an extreme accuracy. This problem can be alleviated if the orthogonal field fastly decays into some states not coupled to the inflaton. Natural candidates for such states can be the right-handed neutrinos. We show that a non-trivial evolution of the classic sneutrino fields after inflation offers an interesting mechanism for generating a correct amount of lepton asymmetry, which being reprocessed by sphalerons can explain the observed baryon asymmetry of the Universe. Our scenario implies interesting bounds for the neutrino masses in the context of seesaw mechanism.

Decoherence in quantum cosmology at the onset of inflation

We calculate the reduced density matrix for the inflaton field in a model of chaotic inflation by tracing out degrees of freedom corresponding to various bosonic fields. Apart from the standard decoherence factor there also arises a contribution from the Euclidean effective action of quantum fields. We regularise the ultraviolet divergences in the decoherence factor. Dimensional regularisation does not work because it would lead to a density matrix which does not define a bounded operator. A conformal redefinition of the environmental fields leads to a bounded density matrix. This redefinition is essentially fixed by the requirement that decoherence be absent for vanishing particle creation. Off-diagonal elements of the reduced density matrix become negligibly small for non-conformally invariant fields, so that due to bosonic fields the Universe can acquire classical properties near the onset of inflation.

Pre-big-bang requires the universe to be exponentially large from the very beginning

We show that in a generic case of the pre-big-bang scenario, inflation will solve cosmological problems only if the universe at the onset of inflation is extremely large and homogeneous from the very beginning. The size of a homogeneous part of the universe at the beginning of the stage of pre-big-bang (PBB) inflation must be greater than $10^{19}$ $l_s$, where $l_s$ is the stringy length. The total mass of an inflationary domain must be greater than $10^{72} M_{s}$, where $M_{s} \sim l_s^{-1}$. If the universe is initially radiation dominated, then its total entropy at that time must be greater than $10^{68}$. If the universe is closed, then at the moment of its formation it must be uniform over $10^{24}$ causally disconnected domains. The natural duration of the PBB stage in this scenario is $M_p^{-1}$. We argue that the initial state of the open PBB universe could not be homogeneous because of quantum fluctuations. Independently of the issue of homogeneity, one must introduce two large dimensionless parameters, $g_0^{-2} > 10^{53}$, and $B > 10^{91}$, in order to solve the flatness problem in the PBB cosmology. A regime of eternal inflation does not occur in the PBB scenario. This should be compared with the simplest versions of the chaotic inflation scenario, where the regime of eternal inflation may begin in a universe of size $O(M_{p}^{-1})$ with vanishing initial radiation entropy, mass $O(M_p)$, and geometric entropy O(1). We conclude that the current version of the PBB scenario cannot replace usual inflation even if one solves the graceful exit problem in this scenario.

Comparison of cortical potentials evoked by mechanical and electrical stimulation of the human oesophagus

BACKGROUND: The pathways mediating Cortical Evoked Potentials (CEP) obtained by mechanical (MS) and electrical (ES) stimulation of the oesophagus remain controversial. Whilst CEP have been recorded with either stimuli, the longer latency of CEP to MS has led to the suggestion that these responses are mediated via unmyelinated C-fibres whereas the shorter latency CEP to ES are mediated via myelinated A-6 fibres. However, a direct comparison of the CEP characteristics in the same subject have not been reported. Aim: To compare oesnphageal CEP obtained by MS and ES. Methods: CEP were recorded from the vertex (Cz) in 6 male subjects (age 25-31) using surface electrodes connected to a signal averager via an amplifier. Stimulation was applied 5cm above the LOS. Electrical Stimulation: Was performed using a bipolar ring electrode connected to a stimulator. Stimulation Intensity (SI) was 75% of the subjects maximum tolerated intensity. A grand average of 200 stimuli were recorded. Mechanical Stimulation: Was performed using a 2cm silicone balloon connected to a pump. SI was set at a level which produced a strong, non-painful sensation. A grand average of 200 stimuli were recorded. The rise time to maximum balloon inflation was constant (165ms). Peak latencies were measured from the onset of inflation. Results: Reproducible, triphasic CEP were evoked in all subjects by ES and MS of the oesopha ~us. Values given as group mean _+ SD.

Inhomogeneity of spatial curvature for inflation

We study how the initial inhomogeneities of the spatial curvature affect the onset of inflation in the closed universe. We consider a cosmological model which contains a radiation and a cosmological constant. In order to treat the inhomogeneities in the closed universe, we improve the long wavelength approximation such that the non-small spatial curvature is tractable in the lowest order. Using the improved scheme, we show how large inhomogeneities of the spatial curvature prevent the occurrence of inflation.

90 STANDARDISATION OF THE HERING-BREUER DEFLATIONARY REFLEX

We have recently reported that the forced partial expiratory flow volume technique induces the Hering-Breuer deflationary reflex in infants. The factors responsible for initiating this reflex in man have never been documented. We investigated the effects of altering the peak and rate of rise of jacket pressure and of inflating the jacket at different times in the respiratory cycle on the strength of the reflex. Reflex strength was determined by the rate of fall of oesophageal pressure post jacket inflation. 28 healthy newborn infants were studied using a “Hammersmith” jacket and pneumotachograph/reverse plethysmograph system. There was a significant relationship between peak oesophageal pressure, reduction in oesophageal pressure post inflation, rate of inflation of jacket and the reflex strength (p<0.001). However, there was no relationship between the position in the respiratory cycle of jacket inflation and reflex strength. The reflex was most reproducible, occurring 0.12-0.16 seconds after onset of inflation, when the jacket inflation pressure was at least 30cms H2O, the rate of rise of the jacket was less than 0.2 seconds and inflation commenced around end inspiration. We recommend that these conditions are used to standardise the Hering-Breuer deflationary reflex.

Generality of inflation in a planar universe.

We study a generality of an inflationary scenario by integrating the Einstein equations numerically in a plane-symmetric spacetime. We consider the inhomogeneous spacetimes due to (i) localized gravitational waves with a positive cosmological constant $\ensuremath{\Lambda}$ and (ii) an inhomogeneous inflation field $\ensuremath{\Phi}$ with a potential $\frac{1}{2}{m}^{2}{\ensuremath{\Phi}}^{2}$. For case (i), we find that any initial inhomogeneities are smoothed out even if waves collide, so that we conclude that inhomogeneity due to gravitational waves does not prevent the onset of inflation. As for case (ii), if the mean value of the inflaton field is initially as large as the condition in an isotropic and homogeneous inflationary model (i.e., the mean value is larger than several times the Planck mass), the field is soon homogenized and the universe always evolves into de Sitter spacetime. This supports the cosmic no hair conjecture in a planar universe. We also discuss the effects of an additional massless scalar field, which are introduced to set initial data in the usual analysis.

Semiclassical effects and the onset of inflation

The author studies the constraint equations of general relativity coupled to a massive Klein-Gordon field, for which he presents a class of exact solutions. He discusses which of these Cauchy data eventually lead to inflation and he concludes that semiclassical effects favor only the inflationary Cauchy data as initial conditions for the classical era.

Regge calculus model of Bianchi IX inflation

The continuous-time 3+1 Regge calculus of Piran-Williams (1986) is applied to analyse a homogeneous anisotropic closed cosmological model. Piran-Williams five-cell model is extended to a 16-cell model, and the action for the lattice is constructed. The Hamiltonian constraint and the evolution equations derived from the action are solved numerically. It is shown that this method works very well for the analysis of the inflation of the homogeneous anisotropic universe. The inflation takes place for most of initial conditions, but in the case where the spatial curvature dominates other energy densities initially, some universes recollapse before the onset of inflation. The effect of the initial anisotropy helps the onset of inflation. The numerical solutions are compared with Wald's (1983) cosmic non-hair theorem and differences between the pure cosmological constant and the effective one are discussed.

Semiclassical effects and the onset of inflation.

We present a class of exact solutions to the constraint equations of General Relativity coupled to a Klein - Gordon field, these solutions being isotropic but not homogeneous. We analyze the subsequent evolution of the consistent Cauchy data represented by those solutions, showing that only certain special initial conditions eventually lead to successfull Inflationary cosmologies. We argue, however, that these initial conditions are precisely the likely outcomes of quantum events occurred before the inflationary era.

Regge calculus model of Bianchi ix inflation

The continuous time 3+1 Regge calculus of Piran-Williams is applied to analyze a homogeneous anisotropic closed cosmological model. Piran-Williams' 5cell model is extended to 16 cell model, and the action for the lattice is constructed. The Hamiltonian constraint and evolution equations derived from the action are solved numerically. It is shown that this method works very well for the analysis of inflation of a homogeneous anisotropic universe. Inflation takes place for most of intial conditions, but in case that spatial curvature dominates other energy density initially, some universes recollapse before onset of inflation. The effect of the intial anisotropy helps the onset of inflation. The numerical solutions are compared with Wald's cosmic no hair theorem and difference between pure cosmological constant and effective one is discussed.

A cosmological field theory

view Abstract Citations (32) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Cosmological Field Theory Starkovich, Steven P. ; Cooperstock, Fred I. Abstract Field theory is used to describe the material content of the universe throughout its entire history, and an oscillating cosmological model without a singularity is presented. The 'cosmological fluid' is described by a single scalar field that undergoes a series of phase transitions, each of which denotes a change in the equation of state of the field. We find that an inflationary equation of state (rho equal to about -p) is required in the early universe if the later epochs are to resemble the standard model. We find that H0 = 33-44 km/s per Mpc is the value of the Hubble parameter at the current epoch that is least sensitive to initial conditions. Unlike most other inflation models, the onset of inflation in our theory is independent of an earlier radiation-dominated era. Instead, inflation arises as a consequence of boundary conditions which are expressed in terms of the fundamental Planck quantities. The heating occurs during inflation, and this imposes a thermodynamic constraint on a more complete theory of matter for the early universe. Inflation continues until a maximum possible physical temperature (the Planck temperature) is attained, at which point a phase transition occurs and the standard model begins. For an arbitrary equation of state, we show that the scalar field potential may be derived from the solution of Riccati's equation. We use this result to find the scalar field Lagrangian for the entire history of the universe. Publication: The Astrophysical Journal Pub Date: October 1992 DOI: 10.1086/171830 Bibcode: 1992ApJ...398....1S Keywords: Cosmology; Field Theory (Physics); Universe; Astronomical Models; Computational Astrophysics; Evolution (Development); Astrophysics; COSMOLOGY: THEORY; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE full text sources ADS |

Thermal spectra in the early Universe

It is shown that curvature effects, though completely negligible at the present day, can drastically alter thermal spectra at early times in some inflationary cosmological models. This can lead to a modification of the thermal history of the universe before the entropy production. The effects are only present for spatially curved k not=0 Robertson-Walker models, not for spatially flat k=0 models. If the entropy increase is >> 1087 and k not=0 then the energy density in the quantum fields is much greater, and hence the universe is much younger, at the onset of inflation than would be the case in a spatially flat universe. The effect is not relevant for chaotic inflation.

Inflation ? an alternative to the singular Big Bang

Domains larger than the horizon in which Φ > (a few) ×M pl are required for the onset of inflation. Two different, equally plausible, arguments lead us to opposite conclusions about the feasibility of the existence of such regions. It seems that inflation does not free us completely from the need for special initial conditions. However, Linde has pointed out that inflation can be eternal. He stresses the fact that inflation will never cease, but this also means that it did not necessarily have a beginning. We argue that this is the simplest solution to the initial value problem and that inflation might not only solve the problems of the Big Bang model, it might also provide us with an alternative that will replace it altogether.

Spherical inhomogeneous cosmologies and inflation: Numerical methods.

We describe a spherically symmetric code for inhomogeneous cosmological problems. Our main goal is to study the onset of inflation under inhomogeneous conditions. We would like to explore the influence of inhomogeneity on inflation. In particular we address the question of whether large inhomogeneity during the very early Universe can prevent the Universe from entering an inflationary era. In this paper we describe the equations, the numerical techniques, tests, and some preliminary results. A detailed discussion of the results will follow in a subsequent paper.

Inflating one's own cuff does not increase self-recorded blood pressure.

To determine whether the muscular activity required to inflate a blood pressure cuff for self-recording influences the blood pressure at the instant of the subsequent measurement, finger blood pressure was recorded continuously during cuff inflation. Ten normotensive and seven untreated hypertensive subjects used their dominant hands to inflate, in 5 s, an occluding cuff on the same arm up to 200 mmHg. Blood pressure in the middle finger of the other arm was measured continuously by the Finapres device. Korotkoff sounds were determined by a microphone in the arm cuff, and the speed of deflation was kept constant by the investigator at 2-3 mmHg/s. Systolic pressure rose at the onset of inflation, with an average peak of 13 +/- 6 (s.d.) and 12 +/- 8 mmHg above baseline in the normotensive and hypertensive subjects, respectively. Five seconds after the onset of deflation both systolic and diastolic pressures in both groups had returned to baseline levels. Thus, self-inflation of a blood pressure cuff allows a valid measurement of blood pressure provided the recommended guidelines are strictly followed.

Anisotropy in the chaotic inflationary universe

The effect of anisotropies on the chaotic inflationary model is investigated for a general class of Bianchi cosmologies. It is shown that for suitable initial conditions of a scalar field any initial anisotropy always disappers before the onset of inflation. Using numerical calculations it is also shown for Bianchi I models that the class initial conditions of the scalar field which leads to inflation is very large.

Respiratory phase locking during mechanical ventilation in anesthetized human subjects.

The coupling patterns between the rhythm of a mechanical ventilator and the rhythm of spontaneous breathing were studied in enflurane-anesthetized adult human subjects. The spontaneous breathing pattern was altered in response to different frequencies and amplitudes of forced lung inflations. A 1:1 phase locking (the frequency of the mechanical ventilator is matched by the frequency of spontaneous breathing with a fixed phase between the 2 rhythms) was observed in a range of up to +/- 40% of some of the subject's spontaneous breathing frequencies. During 1:1 phase locking, there were marked changes in the expiratory duration as measured from the electromyogram of the diaphragm. The phase relationship between onset of inflation and onset of inspiration depended on the frequency and amplitude of mechanical inflation. At ventilator settings that did not give 1:1 phase locking, other simple phase-locked patterns, such as 1:2 and 2:1, or irregular non-phase-locked patterns were observed. Reflexes arising from lung inflation, which may underlie the entrainment, are discussed in the context of these results.

Minimum amount of inflation to solve the flatness and horizon problems.

In this note we show that for natural initial conditions at the Planck time the horizon problem requires only twice as much inflation for its solution as does the flatness problem. We further argue that with these initial conditions the Universe is open rather than closed, and was dominated by gravitational curvature at the onset of inflation.