Marco Litterio - Academia.edu (original) (raw)
Papers by Marco Litterio
Vistas in Astronomy, 1993
ABSTRACT The astronomical interest of double inflation stems from the possibility it gives of ins... more ABSTRACT The astronomical interest of double inflation stems from the possibility it gives of inserting a feature in an otherwise featureless (or scale invariant) perturbation spectrum, precisely at the scale (100 Mpc , say) that goes through the horizon at the (sharp) separations between the two successive inflations. Double inflation occurs when two scalar fields (or inflatons ) dominate sequentially the cosmic expansion or when vacuum polarization Ricci scalar R squared added to the Lagrangian is taken into account and only one inflaton is present. (This perhaps is more natural as it exploits quantum effects to reduce to one the number of the ad hoc ingredients.) In that case we know from Starobinsky's pioneering work that the first inflation is driven by R rightly called then scalaron under the rules of Fourth Order Gravity, (FOG), while the second is driven by under the rules of ordinary General Relativity, (GR). Unfortunately most of the appeal of the scalaron-inflaton scenario in relation to the feature in the perturbation spectrum, is lost because a delicate fine tuning of the value of the (second) inflaton at the beginning of the second inflation is required, in the absence of which the two inflations merge in one and no scale is singled out. In order to overcome this difficulty, we introduce in the Lagrangian density a new scalar coupling between and R 2 , analogous to the well known non minimal coupling between and R of canonical GR. We show that in this way the two inflationary episodes of FOG and GR may be neatly distinguished from each other, regardless of the initial value of . This is due to the influence of the coupling on the shape of the conformal potential, in which one can easily carve a channel of evolution, consisting in fact of two orthogonal valleys. Then, for most of phase space the attractor is this doubly inflationary trajectory that lies at the bottom of the two valleys (Fig. 1). In fact, in this case the Universe first rolls down to the bottom of the first valley where the inflaton takes the desired value, and then goes on the course sketched above, consisting of the FOG inflation driven by the scalaron and the GR inflation driven by the inflaton. Numerical examples are given (Fig.2). In conclusion it is pointed out that this engineering of the conformal potential may also be exploited, perhaps more interestingly, far beyond the original motivation of this work: for example, to generate bubbles of astrophysical interest in a sort of first-order inflation, which does not have the graceful exit problem of old inflation and has been accordingly nicknamed by us getaway inflation (Fig. 3).
Physical Review D, 1992
A new way to couple first-order phase transitions to inflation is proposed. The mechanism, dubbed... more A new way to couple first-order phase transitions to inflation is proposed. The mechanism, dubbed getaway inflation, bypasses the problem of the" graceful exit" by letting the inflationary phase of the background have a classical end. At the same time, a stage of ...
Vacuum multidimensional cosmological models with internal spaces being compact n-dimensional Lie ... more Vacuum multidimensional cosmological models with internal spaces being compact n-dimensional Lie group manifolds are considered. Products of 3-spheres and SU(3) manifold (a novelty in cosmology) are studied. It turns out that the dynamical evolution of the internal space drives an accelerated expansion of the external world (power law inflation). This generic solution (attractor in a phase space) is determined by the Lie group space without any fine tuning or arbitrary inflaton potentials. Matter in the four dimensions appears in the form of a number of scalar fields representing anisotropic scale factors for the internal space. Along the attractor solution the volume of the internal space grows logarithmically in time. This simple and natural model should be completed by mechanisms terminating the inflationary evolution and transforming the geometric scalar fields into ordinary particles. ⋆ Corresponding author;
The possibility that inflation may trigger an instability in compactification of extra spatial di... more The possibility that inflation may trigger an instability in compactification of extra spatial dimensions is considered. In old, new, or extended inflation, the false vacuum energy results in a semiclassical instability in which the scalar field representing the radius of the extra dimensions may tunnel through a potential barrier leading to an expansion of the internal space. In chaotic inflation, if the initial value of the scalar field responsible for inflation is large enough, the internal space becomes cIassically unstable to ever increasing expansion. Restrictions on inflationary models necessary to keep the extra dimensions small are discussed. (NASA-CR-I_6597) STABILITY Og
Following a suggestion by Gasperini and Veneziano, that String Cosmology can be reconciled with I... more Following a suggestion by Gasperini and Veneziano, that String Cosmology can be reconciled with Inflation and, hence, with the Standard Big Bang, we display an analytical solution which possesses four interesting properties: (1) it is non-singular; (2) it distinguishes the dynamics of the external scale factor, a(t), from that of the internal one, b(t); (3) it exhibits a non-monotonic behavior of a(t); and (4) it stabilizes both Newton’s constant and b(t) (the latter to a finite, non-vanishing value). The interest of the non-monotonic evolution of a(t) consists in the fact that it contains three phases of accelerated expansion, contraction and expansion before the final decelerated expansion which eventually becomes the Standard Big Bang. The total number of e-folds of the three accelerated eras can be calculated and tuned to fit the requests of observational astronomy. 1 Typeset using REVTEXI. INTRODUCTION.
Vacuum multidimensional cosmological models with internal spaces being compact n-dimensional Lie ... more Vacuum multidimensional cosmological models with internal spaces being compact n-dimensional Lie group manifolds are considered. Products of 3-spheres and SU(3) manifold (a novelty in cosmology) are studied. It turns out that the dynamical evolution of the internal space drives an accelerated expansion of the external world (power law inflation). This generic solution (attractor in a phase space) is determined by the Lie group space without any fine tuning or arbitrary inflaton potentials. Matter in the four dimensions appears in the form of a number of scalar fields representing anisotropic scale factors for the internal space. Along the attractor solution the volume of the internal space grows logarithmically in time. This simple and natural model should be completed by mechanisms terminating the inflationary evolution and transforming the geometric scalar fields into ordinary particles. ⋆ Corresponding author; e-mail address: litterio@astrom.astro.it; fax: 39-6-4403673
It is shown that electromagnetic waves initially emitted towards the higher dimensions cannot eme... more It is shown that electromagnetic waves initially emitted towards the higher dimensions cannot emerge in the physical external space-time as ordinary photons. Two frequencies can be assigned to an ordinary photon: one associated with the physical 4-space and the other with the total space-time. It is a general property of known multidimensional cosmologies] solutions that the latter decreases in time (redshift) while the former increases (blueshifi).
General Relativity and Gravitational Physics, 1991
Ijmpa, 1991
Abstract The energy spectrum and stability of the effective theory resulting from the Einstein-Ga... more Abstract The energy spectrum and stability of the effective theory resulting from the Einstein-Gauss-Bonnet gravity theory with compactified internal space are investigated. The internal space can evolve in its volume and/or shape, giving rise to a system of scalar fields in the ...
Ijmpa, 1990
The Phase Space portrait of a cosmological model with a scalar field coupled to curvature is disc... more The Phase Space portrait of a cosmological model with a scalar field coupled to curvature is discussed in detail, analytically and numerically, for any value of the coupling constant ξ and any power law (ϕ2n) potential. The results, particularly intuitive from the graphical point of view, generalize previous studies on the phase space with minimal coupling (ξ = 0) and quadratic or quartic potentials to the entire parameter space (ξ, n). We find global inflationary attractors, often in analytical form, with or without the correct Friedmannian limit. If the coupling constant is negative, escaping regions may occur, while, if it is positive, a forbidden region cuts out a large part of the phase space. Semiclassical instability of vacuum states and singularity-free trajectories are also discussed.
It is shown that electromagnetic waves initially emitted towards the higher dimensions cannot eme... more It is shown that electromagnetic waves initially emitted towards the higher dimensions cannot emerge in the physical external space-time as ordinary photons. Two frequencies can be assigned to an ordinary photon: one associated with the physical 4-space and the other with the total space-time. It is a general property of known multidimensional cosmologies] solutions that the latter decreases in time (redshift) while the former increases (blueshifi).
Astronomy & Astrophysics, 2000
The Crab Nebula and the Pulsar have been pointed several times by the BeppoSAX satellite. We anal... more The Crab Nebula and the Pulsar have been pointed several times by the BeppoSAX satellite. We analysed all these observations, summed together, to study the main spectral properties with a good phase resolution. A new accurate estimate of the hydrogen column density in the Crab direction NH=3.23x1021 cm-2 is given as derived from the analysis of the off-pulse emission at
Nuclear Physics B - Proceedings Supplements, 2004
We report the results of the temporal and spectral analysis of the longest BeppoSAX pointing (abo... more We report the results of the temporal and spectral analysis of the longest BeppoSAX pointing (about 770 ks) of the microquasar GRS 1915+105, performed in October 2000. For the largest fraction of the observation GRS 1915+105 was in the so called ρ-mode, characterized by series of sharp pulses with a typical recurrence time of about 50 s, well detectable in the energy range 2-10 keV. This quasi-periodic behaviour was generally quite stable but, occasionally, it changed to a more irregular state in which the pulses are broader and their recurrence time is highly fluctuating. We found that this irregular ρ-mode is associated with an enhanced emission at energies greater than 15 keV. Wavelet analysis of the (2−10 keV) light curves is used to study the time evolution of the ρ-mode.
Nuclear Physics B - Proceedings Supplements, 1999
ABSTRACT
Physics Letters B, 1996
Vacuum multidimensional cosmological models with internal spaces being compact n-dimensional Lie ... more Vacuum multidimensional cosmological models with internal spaces being compact n-dimensional Lie group manifolds are considered. Products of 3-spheres and SU (3) manifold (a novelty in cosmology) are studied. It turns out that the dynamical evolution of the internal space drives an accelerated expansion of the external world (power law inflation). This generic solution (attractor in a phase space) is determined by the Lie group space without any fine tuning or arbitrary inflaton potentials. Matter in the four dimensions appears in the form of a number of scalar fields representing anisotropic scale factors for the internal space. Along the attractor solution the volume of the internal space grows logarithmically in time. This simple and natural model should be completed by mechanisms terminating the inflationary evolution and transforming the geometric scalar fields into ordinary particles.
Lecture Notes in Physics, 1995
Without Abstract
Lecture Notes in Physics, 1995
Without Abstract
Vistas in Astronomy, 1993
ABSTRACT The astronomical interest of double inflation stems from the possibility it gives of ins... more ABSTRACT The astronomical interest of double inflation stems from the possibility it gives of inserting a feature in an otherwise featureless (or scale invariant) perturbation spectrum, precisely at the scale (100 Mpc , say) that goes through the horizon at the (sharp) separations between the two successive inflations. Double inflation occurs when two scalar fields (or inflatons ) dominate sequentially the cosmic expansion or when vacuum polarization Ricci scalar R squared added to the Lagrangian is taken into account and only one inflaton is present. (This perhaps is more natural as it exploits quantum effects to reduce to one the number of the ad hoc ingredients.) In that case we know from Starobinsky's pioneering work that the first inflation is driven by R rightly called then scalaron under the rules of Fourth Order Gravity, (FOG), while the second is driven by under the rules of ordinary General Relativity, (GR). Unfortunately most of the appeal of the scalaron-inflaton scenario in relation to the feature in the perturbation spectrum, is lost because a delicate fine tuning of the value of the (second) inflaton at the beginning of the second inflation is required, in the absence of which the two inflations merge in one and no scale is singled out. In order to overcome this difficulty, we introduce in the Lagrangian density a new scalar coupling between and R 2 , analogous to the well known non minimal coupling between and R of canonical GR. We show that in this way the two inflationary episodes of FOG and GR may be neatly distinguished from each other, regardless of the initial value of . This is due to the influence of the coupling on the shape of the conformal potential, in which one can easily carve a channel of evolution, consisting in fact of two orthogonal valleys. Then, for most of phase space the attractor is this doubly inflationary trajectory that lies at the bottom of the two valleys (Fig. 1). In fact, in this case the Universe first rolls down to the bottom of the first valley where the inflaton takes the desired value, and then goes on the course sketched above, consisting of the FOG inflation driven by the scalaron and the GR inflation driven by the inflaton. Numerical examples are given (Fig.2). In conclusion it is pointed out that this engineering of the conformal potential may also be exploited, perhaps more interestingly, far beyond the original motivation of this work: for example, to generate bubbles of astrophysical interest in a sort of first-order inflation, which does not have the graceful exit problem of old inflation and has been accordingly nicknamed by us getaway inflation (Fig. 3).
Physical Review D, 1992
A new way to couple first-order phase transitions to inflation is proposed. The mechanism, dubbed... more A new way to couple first-order phase transitions to inflation is proposed. The mechanism, dubbed getaway inflation, bypasses the problem of the" graceful exit" by letting the inflationary phase of the background have a classical end. At the same time, a stage of ...
Vacuum multidimensional cosmological models with internal spaces being compact n-dimensional Lie ... more Vacuum multidimensional cosmological models with internal spaces being compact n-dimensional Lie group manifolds are considered. Products of 3-spheres and SU(3) manifold (a novelty in cosmology) are studied. It turns out that the dynamical evolution of the internal space drives an accelerated expansion of the external world (power law inflation). This generic solution (attractor in a phase space) is determined by the Lie group space without any fine tuning or arbitrary inflaton potentials. Matter in the four dimensions appears in the form of a number of scalar fields representing anisotropic scale factors for the internal space. Along the attractor solution the volume of the internal space grows logarithmically in time. This simple and natural model should be completed by mechanisms terminating the inflationary evolution and transforming the geometric scalar fields into ordinary particles. ⋆ Corresponding author;
The possibility that inflation may trigger an instability in compactification of extra spatial di... more The possibility that inflation may trigger an instability in compactification of extra spatial dimensions is considered. In old, new, or extended inflation, the false vacuum energy results in a semiclassical instability in which the scalar field representing the radius of the extra dimensions may tunnel through a potential barrier leading to an expansion of the internal space. In chaotic inflation, if the initial value of the scalar field responsible for inflation is large enough, the internal space becomes cIassically unstable to ever increasing expansion. Restrictions on inflationary models necessary to keep the extra dimensions small are discussed. (NASA-CR-I_6597) STABILITY Og
Following a suggestion by Gasperini and Veneziano, that String Cosmology can be reconciled with I... more Following a suggestion by Gasperini and Veneziano, that String Cosmology can be reconciled with Inflation and, hence, with the Standard Big Bang, we display an analytical solution which possesses four interesting properties: (1) it is non-singular; (2) it distinguishes the dynamics of the external scale factor, a(t), from that of the internal one, b(t); (3) it exhibits a non-monotonic behavior of a(t); and (4) it stabilizes both Newton’s constant and b(t) (the latter to a finite, non-vanishing value). The interest of the non-monotonic evolution of a(t) consists in the fact that it contains three phases of accelerated expansion, contraction and expansion before the final decelerated expansion which eventually becomes the Standard Big Bang. The total number of e-folds of the three accelerated eras can be calculated and tuned to fit the requests of observational astronomy. 1 Typeset using REVTEXI. INTRODUCTION.
Vacuum multidimensional cosmological models with internal spaces being compact n-dimensional Lie ... more Vacuum multidimensional cosmological models with internal spaces being compact n-dimensional Lie group manifolds are considered. Products of 3-spheres and SU(3) manifold (a novelty in cosmology) are studied. It turns out that the dynamical evolution of the internal space drives an accelerated expansion of the external world (power law inflation). This generic solution (attractor in a phase space) is determined by the Lie group space without any fine tuning or arbitrary inflaton potentials. Matter in the four dimensions appears in the form of a number of scalar fields representing anisotropic scale factors for the internal space. Along the attractor solution the volume of the internal space grows logarithmically in time. This simple and natural model should be completed by mechanisms terminating the inflationary evolution and transforming the geometric scalar fields into ordinary particles. ⋆ Corresponding author; e-mail address: litterio@astrom.astro.it; fax: 39-6-4403673
It is shown that electromagnetic waves initially emitted towards the higher dimensions cannot eme... more It is shown that electromagnetic waves initially emitted towards the higher dimensions cannot emerge in the physical external space-time as ordinary photons. Two frequencies can be assigned to an ordinary photon: one associated with the physical 4-space and the other with the total space-time. It is a general property of known multidimensional cosmologies] solutions that the latter decreases in time (redshift) while the former increases (blueshifi).
General Relativity and Gravitational Physics, 1991
Ijmpa, 1991
Abstract The energy spectrum and stability of the effective theory resulting from the Einstein-Ga... more Abstract The energy spectrum and stability of the effective theory resulting from the Einstein-Gauss-Bonnet gravity theory with compactified internal space are investigated. The internal space can evolve in its volume and/or shape, giving rise to a system of scalar fields in the ...
Ijmpa, 1990
The Phase Space portrait of a cosmological model with a scalar field coupled to curvature is disc... more The Phase Space portrait of a cosmological model with a scalar field coupled to curvature is discussed in detail, analytically and numerically, for any value of the coupling constant ξ and any power law (ϕ2n) potential. The results, particularly intuitive from the graphical point of view, generalize previous studies on the phase space with minimal coupling (ξ = 0) and quadratic or quartic potentials to the entire parameter space (ξ, n). We find global inflationary attractors, often in analytical form, with or without the correct Friedmannian limit. If the coupling constant is negative, escaping regions may occur, while, if it is positive, a forbidden region cuts out a large part of the phase space. Semiclassical instability of vacuum states and singularity-free trajectories are also discussed.
It is shown that electromagnetic waves initially emitted towards the higher dimensions cannot eme... more It is shown that electromagnetic waves initially emitted towards the higher dimensions cannot emerge in the physical external space-time as ordinary photons. Two frequencies can be assigned to an ordinary photon: one associated with the physical 4-space and the other with the total space-time. It is a general property of known multidimensional cosmologies] solutions that the latter decreases in time (redshift) while the former increases (blueshifi).
Astronomy & Astrophysics, 2000
The Crab Nebula and the Pulsar have been pointed several times by the BeppoSAX satellite. We anal... more The Crab Nebula and the Pulsar have been pointed several times by the BeppoSAX satellite. We analysed all these observations, summed together, to study the main spectral properties with a good phase resolution. A new accurate estimate of the hydrogen column density in the Crab direction NH=3.23x1021 cm-2 is given as derived from the analysis of the off-pulse emission at
Nuclear Physics B - Proceedings Supplements, 2004
We report the results of the temporal and spectral analysis of the longest BeppoSAX pointing (abo... more We report the results of the temporal and spectral analysis of the longest BeppoSAX pointing (about 770 ks) of the microquasar GRS 1915+105, performed in October 2000. For the largest fraction of the observation GRS 1915+105 was in the so called ρ-mode, characterized by series of sharp pulses with a typical recurrence time of about 50 s, well detectable in the energy range 2-10 keV. This quasi-periodic behaviour was generally quite stable but, occasionally, it changed to a more irregular state in which the pulses are broader and their recurrence time is highly fluctuating. We found that this irregular ρ-mode is associated with an enhanced emission at energies greater than 15 keV. Wavelet analysis of the (2−10 keV) light curves is used to study the time evolution of the ρ-mode.
Nuclear Physics B - Proceedings Supplements, 1999
ABSTRACT
Physics Letters B, 1996
Vacuum multidimensional cosmological models with internal spaces being compact n-dimensional Lie ... more Vacuum multidimensional cosmological models with internal spaces being compact n-dimensional Lie group manifolds are considered. Products of 3-spheres and SU (3) manifold (a novelty in cosmology) are studied. It turns out that the dynamical evolution of the internal space drives an accelerated expansion of the external world (power law inflation). This generic solution (attractor in a phase space) is determined by the Lie group space without any fine tuning or arbitrary inflaton potentials. Matter in the four dimensions appears in the form of a number of scalar fields representing anisotropic scale factors for the internal space. Along the attractor solution the volume of the internal space grows logarithmically in time. This simple and natural model should be completed by mechanisms terminating the inflationary evolution and transforming the geometric scalar fields into ordinary particles.
Lecture Notes in Physics, 1995
Without Abstract
Lecture Notes in Physics, 1995
Without Abstract