arXiv subjects

Eduardo I. Guendelman

Publications and source records attributed to Eduardo I. Guendelman.

At least 37 records · Page 2Linked to original sources

arXiv2019

Inflation from fermions with curvature-dependent mass

A model of inflation realization driven by fermions with curvature-dependent mass is studied. Such a term is derived from the Covariant Canonical Gauge Theory of gravity (CCGG) incorporating Dirac fermions. We obtain an initial de Sitter phase followed by a successful exit, and moreover, we acquire the subsequent thermal history, with an effective matter era, followed finally by a dark-energy epoch. This behavior is a result of the effective `weakening' of gravity at early times, due to the decreased curvature-dependent fermion mass. Through the perturbation level, we obtain the scalar spectral index and the tensor-to-scalar ratio, which are in agreement with the Planck observations. The efficiency of inflation from fermions with curvature-dependent mass, at both the background and perturbation level, reveals the capabilities of the scenario and makes it a good candidate for the description of nature.

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arXiv2019

Dark energy and dark matter unification from dynamical space time: observational constraints and cosmological implications

A recently proposed Dynamical Space-time Cosmology (DSC) that unifies dark energy and dark matter is studied. The general action of this scenario includes a Lagrange multiplier, which is coupled to the energy momentum tensor and a scalar field which is different from quintessence. First for various types of potentials we implement a critical point analysis and we find solutions which lead to cosmic acceleration and under certain conditions to stable late-time attractors. Then the DSC cosmology is confronted with the latest cosmological data from low-redshift probes, namely measurements of the Hubble parameter and standard candles (Pantheon SnIa, Quasi-stellar objects). Performing an overall likelihood analysis and using the appropriate information criteria we find that the explored DSC models are in very good agreement with the data. We also find that one of the DSC models shows a small but non-zero deviation from $Λ$ cosmology, nevertheless the confidence level is close to $\sim 1.5σ$.

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arXiv2019

Two scalar fields inflation from scale-invariant gravity with modified measure

A new class of gravity-matter model defined with an independent non-Riemannian volume form is studied, in the second order formalism. The action has a global scale invariance symmetry, which can be broken by the equation of motion of the measure fields. By a conformal transformation the theory transforms into a theory which governed by two independent scalar fields and a specific potential. When the scale invariance symmetry is not broken also in the equations of motion, only one field appear in the effective potential. This effective potential has a flat region which is responsible for the inflation, and it ends with a minimum, which is responsible for the present vacuum energy. In the general case, with a spontaneous symmetry breaking of the scale symmetry, one scalar field is responsible for the inflation and the other could be responsible for the particle creation. The first field (inflaton) can slowly roll, while the second field (curvaton) is more strongly coupled to the potential. The number of e-folds for both models is also dissuaded and could be constraint in the future.

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arXiv2018

Quadratic curvature theories formulated as Covariant Canonical Gauge theories of Gravity

The Covariant Canonical Gauge theory of Gravity is generalized by including at the Lagrangian level all possible quadratic curvature invariants. In this approach, the covariant Hamiltonian principle and the canonical transformation framework are applied to derive a Palatini type gauge theory of gravity. The metric $g_{μν}$, the affine connection $γ\indices{^λ_{μν}}$ and their respective conjugate momenta, $k^{μνσ}$ and $q\indices{_η^{αξβ}}$ tensors, are the independent field components describing the gravity. The metric is the basic dynamical field, and the connection is the gauge field. The torsion-free and metricity-compatible version of the space-time Hamiltonian is built from all possible invariants of the $q\indices{_η^{αξβ}}$ tensor components up to second order. These correspond in the Lagrangian picture to Riemann tensor invariants of the same order. We show that the quadratic tensor invariant is necessary for constructing the canonical momentum field from the gauge field derivatives, and hence for transforming between Hamiltonian and Lagrangian pictures. Moreover, the theory is extended by dropping metric compatibility and enforcing conformal invariance. This approach could be used for the quantization of the quadratic curvature theories, as for example in the case of conformal gravity.

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arXiv2018

Linear potentials in galaxy halos by Asymmetric Wormholes

A spherically symmetric space-time solution for a diffusive two measures theory is studied. An asymmetric wormhole geometry is obtained where the metric coefficients have a linear term for galactic distances and the analysis of Mannheim and collaborators, can then be used to describe the galactic rotation curves. For cosmological distances, a de-Sitter space-time is realized. Centre of gravity coordinates for the wormhole is introduced which are the most suitable for the collective motion of a wormhole. The wormholes connect universes with different vacuum energy densities which may represent different universes in a "landscape scenario". The metric coefficients depend on the asymmetric wormhole parameters. The coefficient of the linear potential is proportional to both the mass of the wormhole and the cosmological constant of the observed universe. Similar results are also expected in other theories like $k$-essence theories, that may support wormholes.

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arXiv2018

Inflation Compactification from Dynamical space time

A mechanism of inflation from higher dimensions compactification is studied. An Early Universe capable of providing exponential growth for some dimensions and exponential contraction for others, giving therefore an explanation for the big size of the observed four dimensional Universe as well as the required smallness of the extra dimensions is obtained. The mechanism is formulated in the context of dynamical space time theory which produces a unified picture of dark energy, dark matter and can also provides a bounce for the volume of the universe. A negative vacuum energy puts an upper bound on the maximum volume and the bounce imposes a lower bound. So that in the early universe the volume oscillates, but in each oscillation the extra dimensions contract exponentially, and the ordinary dimension expand exponentially. The dynamical space time theory provides a natural way to exit from the inflation compactification epoch since the scalar field that drives the vacuum energy can smoothly climb into small positive values of vacuum energy, which is the end of the inflation compactification. A semi analytic solution for a step function potential is also studied, where all of these effects are shown. Especially the jump of the vacuum energy affect only on the derivative of dynamical space time vector field, and not the volume or it's derivatives, which match smoothly.

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arXiv2018

A correspondence between $1^{st}$ and $2^{nd}$ order formalism by a metricity constraint

A way to obtain a correspondence between the first order and second order formalism is studied. By introducing a Lagrange multiplier coupled to the covariant derivative of the metric, a metricity constraint is implemented. The new contributions which comes from the variation of the Lagrange multiplier transforms the field equations from the first order to the second order formalism, yet the action is formulated in the first order. In this way all the higher derivatives terms in the second order formalism appear as derivatives of the Lagrange multiplier. Using the same method for breaking metricity condition and building conformal invariant theory is briefly discussed, so the method goes beyond just the study of first order or second formulations of gravity, in fact vast new possible theories of gravity are envisioned this way.

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arXiv2018

A transition between bouncing hyper-inflation to ΛCDM from diffusive scalar fields

We consider the history of the universe from a possible big bang or a bounce into a late period of a unified interacting dark energy - dark matter model. The model is based on the Two Measures Theories (T.M.T.) which introduces a metric independent volume element and this allows us to construct a unification of dark energy and dark matter. A generalization of the T.M.T. gives a diffusive non-conservative stress energy momentum tensor in addition to the conserved stress energy tensor which appear in Einstein equations. These leads to a formulation of interacting DE-DM dust models in the form of a diffusive type interacting Unified Dark Energy and Dark Matter scenario. The deviation from $Λ$CDM is determined by the diffusion constant $C_2$. For $C_2=0$ the model is indistinguishable from $Λ$CDM. Numerical solutions of the theories show that in some $C_2 \neq 0$ the evolution of the early universe is governed by Stiff equation of state or the universe bounces to hyper inflation. But all of those solutions have a final transition to $Λ$CDM as a stable fixed point for the late universe.

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arXiv2018

Unified Dark Energy and Dark Matter from Dynamical Space Time

A unification of dark matter and dark energy based on a dynamical space time theory is suggested. By introducing a dynamical space time vector field $χ_μ$ as a Lagrange multiplier, a conservation of an energy momentum tensor $T^{μν}_{(χ)}$ is implemented. This Lagrangian generalizes the "Unified dark energy and dark matter from a scalar field different from quintessence" [Phys.RevD 81, 043520 (2010)] which did not consider a Lagrangian formulation. This generalization allows the solutions which were found previously, but in addition to that also non singular bouncing solutions that rapidly approach to the $Λ$CDM model. The dynamical time vector field exactly coincides with the cosmic time for the a $Λ$CDM solution and suffers a slight shift (advances slower) with respect to the cosmic time in the region close to the bounce for the bouncing non singular solutions. In addition we introduced some exponential potential which could enter into the $T^{μν}_{(χ)}$ stress energy tensor or coupled directly to the measure $\sqrt{-g}$, gives a possible interaction between DE and DM and could explain the coincidence problem.

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arXiv2017

Finding Schwarzschild metric component grr and FLRW's k without solving the Einstein's equation, rather by a synergistic matching between geometric results enfranchised by Newtonian gravity

As is well known, some aspects of General Relativity and Cosmology can be reproduced without even using Einstein's equation. As an illustration, the 0 - 0 component of the Schwarzschild space can be obtained by the requirement that the geodesic of slowly mov- ing particles match the Newtonian equation. Given this result, we shall show here that the remaining component (grr) can be obtained by requiring that the inside of a Newtonian ball of dust matched at a free falling radius with the external space of unspecified type. This matching determines the external space to be of Schwarzschild type. By this, it is also possi- ble to determine that the constant of integration that appears in the Newtonian Cosmology, coincides with the spatial curvature of the FLRW metric. All we assumed was some classical boundary conditions and basic assumptions.

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arXiv2016

Classically and Quantum stable Emergent Universe from Conservation Laws

It has been recently pointed out by Mithani-Vilenkin that certain emergent universe scenarios which are classically stable are nevertheless unstable semiclassically to collapse. Here, we show that there is a class of emergent universes derived from scale invariant two measures theories with spontaneous symmetry breaking (s.s.b) of the scale invariance, which can have both classical stability and do not suffer the instability pointed out by Mithani-Vilenkin towards collapse. We find that this stability is due to the presence of a symmetry in the "emergent phase", which together with the non linearities of the theory, does not allow that the FLRW scale factor to be smaller that a certain minimum value $a_0$ in a certain protected region.

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arXiv2015

Curvaton reheating in a Scale Invariant Two Measures Theory

The curvaton reheating mechanism in a Scale Invariant Two Measures Theory defined in terms of two independent non-Riemannian volume forms (alternative generally covariant integration measure densities) on the space-time manifold which are metric independent is studied. The model involves two scalar matter fields, a dilaton, that transforms under scale transformations and it will be used also as the inflaton of the model and another scalar, which does not transform under scale transformations and which will play the role of a curvaton field. Potentials of appropriate form so that the pertinent action is invariant under global Weyl-scale symmetry are introduced. Scale invariance is spontaneously broken upon integration of the equations of motion. After performing transition to the physical Einstein frame we obtain: (i) For given value of the curvaton field an effective potential for the scalar field with two flat regions for the dilaton which allows for a unified description of both early universe inflation as well as of present dark energy epoch;(iii) In the phase corresponding to the early universe, the curvaton has a constant mass and can oscillate decoupled from the dilaton and that can be responsible for both reheating and perturbations in the theory. In this framework, we obtain some interesting constraints on different parameters that appear in our model; (iii) For a definite parameter range the model possesses a non-singular "emergent universe" solution which describes an initial phase of evolution that precedes the inflationary phase. Finally we discuss generalizations of the model, through the effect of higher curvature terms, where inflaton and curvaton can have coupled oscillations.

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arXiv2015

Schwarzschild and Friedmann Lemaître Robertson Walker metrics from Newtonian Gravitational collapse

As it is well known, the $0-0$ component of the Schwarzschild space can be obtained by the requirement that the geodesic of slowly moving particles match the Newtonian equation. Given this result, we show here that the remaining components can be obtained by requiring that the inside of a Newtonian ball of dust matched at a free falling radius with the external space determines that space to be Schwarzschild, if no pathologies exist. Also we are able to determine that the constant of integration that appears in the Newtonian Cosmology coincides with the spacial curvature of the FLRW metric.

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arXiv2015

The Schwarzschild metric and the Friedmann equations from Newtonian Gravitational collapse

As is well known, the 0 - 0 component of the Schwarzschild space can be obtained by the requirement that the geodesic of slowly moving particles match the Newtonian equation. Given this result, we show here that the remaining components can be obtained by requiring that the inside of a Newtonian ball of dust matched at a free falling radius with the external space determines that space to be Schwarzschild, if no pathologies exist. Also we are able to determine that the constant of integration that appears in the Newtonian Cosmology, coincides with the spatial curvature of the FLRW metric. These results are of interest at least in two respects, one from the point of view of its pedagogical value of teaching General Relativity without in fact using Einstein's equation and second, the fact that some results attributed to General Relativity can be obtained without using General Relativity indicates that these results are more general than the particular dynamics specified by General Relativity.

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arXiv2014

Confining Boundary conditions from dynamical Coupling Constants for Abelian and non Abelian symmetries

In this paper we present a model which can produce boundary confining condition on Dirac field interacting with Abelian or non Abelian gauge fields. The constraint is generated by a scalar field. This kind of model can be the foundation for bag models which can produce confinement. The present work represents among other things a generalization to the non Abelian case of our previous result where the Abelian case was studied. In the $U(1)$ case the coupling to the gauge field contains a term of the form $g(ϕ)j_μ(A^μ +\partial^μB)$ where $B$ is an auxiliary field and $j_μ$ is the Dirac current. The scalar field $ϕ$ determines the local value of the coupling of the gauge field to the Dirac particle. The consistency of the equations determines the condition $\partial^μϕj_μ= 0$ which implies that the Dirac current cannot have a component in the direction of the gradient of the scalar field. As a consequence, if $ϕ$ has a soliton behavior, like defining a bubble that connects two vacuua, we obtain that the Dirac current cannot have a flux through the wall of the bubble, defining a confinement mechanism where the fermions are kept inside those bags. In this paper we present more models in Abelian case which produce constraint on the Dirac or scalar current and also spin. Furthermore a model that give the M.I.T confinement condition for gauge fields is obtained. We generalize this procedure for the non Abelian case and we find a constraint that can be used to build a bag model. In the non Abelian case the confining boundary conditions hold at a specific surface of a domain wall.

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arXiv2014

Scalar gauge fields

In this paper we give a variation of the gauge procedure which employs a scalar gauge field, $B (x)$, in addition to the usual vector gauge field, $A_μ(x)$. We study this variant of the usual gauge procedure in the context of a complex scalar, matter field $ϕ(x)$ with a U(1) symmetry. We will focus most on the case when $ϕ$ develops a vacuum expectation value via spontaneous symmetry breaking. We find that under these conditions the scalar gauge field mixes with the Goldstone boson that arises from the breaking of a global symmetry. Some other interesting features of this scalar gauge model are: (i) The new gauge procedure gives rise to terms which violate C and CP symmetries. This may have have applications in cosmology or for CP violation in particle physics; (ii) the existence of mass terms in the Lagrangian which respect the new extended gauge symmetry. Thus one can have gauge field mass terms even in the absence of the usual Higgs mechanism; (iii) the emergence of a sine-Gordon potential for the scalar gauge field; (iv) a natural, axion-like suppression of the interaction strength of the scalar gauge boson.

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arXiv2014

Scale Symmetry Breaking From Total Derivative Densities and the Cosmological Constant Problem

The use in the action integral of totally divergent densities in generally coordinate invariant theories can lead to interesting mechanisms of spontaneous symmetry breaking of scale invariance. With dependence in the action on a metric independent density $Φ$, in $4D$ , we can define $Φ=\varepsilon^{μναβ}\partial_μA_{ναβ}$ that gives a new interesting mechanism for breaking scale symmetry in 4-D theories of gravity plus matter fields, through the $A_{ναβ}$ equations of motion which lead to an integration constant the breaks the scale symmetry, while introducing terms of the form $eG ln K$ , $e$ being the determinant of the vierbein, $G$ being the Gauss Bonnet scalar and $K$ being scalar functions of the fields transforming like $K \rightarrow cK $ (where c is a constant) under a scale transformation. Such a term is invariant only up to a total divergence and therefore leads to breaking of scale invariance due to gravitational instantons. The topological density constructed out of gauge field strengths $\varepsilon^{μναβ}F^a_{μν}F^a_{αβ}$ can be coupled to the dilaton field linearly to produce a scale invariant term up to a total divergence. The scale symmetry can be broken by Yang Mills instantons which lead to a very small vacuum energy for our Universe.

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arXiv2013

Unified Dark Energy-Dark Matter model with Inverse Quintessence

We consider a model where both dark energy and dark matter originate from the coupling of a scalar field with a non-conventional kinetic term to, both, a metric measure and a non-metric measure. An interacting dark energy/dark matter scenario can be obtained by introducing an additional scalar that can produce non constant vacuum energy and associated variations in dark matter. The phenomenology is most interesting when the kinetic term of the additional scalar field is ghost-type, since in this case the dark energy vanishes in the early universe and then grows with time. This constitutes an "inverse quintessence scenario", where the universe starts from a zero vacuum energy density state, instead of approaching it in the future.

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