Dynamics Of Scalar Field Research Articles

Universality in the relaxation dynamics of the composed black-hole-charged-massive-scalar-field system: The role of quantum Schwinger discharge

The quasinormal resonance spectrum {ωn(μ,q,M,Q)}n=0n=∞ of charged massive scalar fields in the charged Reissner–Nordström black-hole spacetime is studied analytically in the large-coupling regime qQ≫Mμ (here {μ,q} are respectively the mass and charge coupling constant of the field, and {M,Q} are respectively the mass and electric charge of the black hole). This physical system provides a striking illustration for the validity of the universal relaxation bound τ×T≥ħ/π in black-hole physics (here τ≡1/ℑω0 is the characteristic relaxation time of the composed black-hole-scalar-field system, and T is the Bekenstein–Hawking temperature of the black hole). In particular, it is shown that the relaxation dynamics of charged massive scalar fields in the charged Reissner–Nordström black-hole spacetime may saturate this quantum time-times-temperature inequality. Interestingly, we prove that potential violations of the bound by light scalar fields are excluded by the Schwinger-type pair-production mechanism (a vacuum polarization effect), a quantum phenomenon which restricts the physical parameters of the composed black-hole-charged-field system to the regime qQ≪M2μ2/ħ.

On the initial state of the Universe in quantum cosmology

The paper discusses the problem of the initial state of a quantum inflationary Universe. Considering the dynamics of the inflation scalar field at the beginning of the inflation stage in the context of semi-classical approximation, we have identified this field with a cosmic time parameter. The early Universe state was defined as an initial value of the inflation field. Other degrees of the Universe freedom, including the scale factor, are treated within the framework of the quantum theory. The initial state of quantum degrees of freedom at the beginning of the inflation must be defined as well. A principle of the least excitation of physical degrees of freedom for the Universe has been proposed to determine the initial state of the quantum Universe. A uniform anisotropic model of the Universe was considered where its size and the anisotropic parameters were quantum dynamical variables. Assuming that the Universe size is a radial variable in the configuration space of the theory, the definition of the Hamiltonian of the Universe is rendered more precise. A simple exponential form of the initial state of the Universe is suggested and the Universe initial size is estimated for this form.

Inflation in maximal gauged supergravities

We discuss the dynamics of multiple scalar fields and the possibility of realistic inflation in the maximal gauged supergravity. In this paper, we address this problem in the framework of recently discovered 1-parameter deformation of SO(4,4) and SO(5,3) dyonic gaugings, for which the base point of the scalar manifold corresponds to an unstable de Sitter critical point. In the gauge-field frame where the embedding tensor takes the value in the sum of the {\\bf 36} and {\\bf 36'} representations of SL(8), we present a scheme that allows us to derive an analytic expression for the scalar potential. With the help of this formalism, we derive the full potential and gauge coupling functions in analytic forms for the SO(3)× SO(3)-invariant subsectors of SO(4,4) and SO(5,3) gaugings, and argue that there exist no new critical points in addition to those discovered so far. For the SO(4,4) gauging, we also study the behavior of 6-dimensional scalar fields in this sector near the Dall'Agata-Inverso de Sitter critical point at which the negative eigenvalue of the scalar mass square with the largest modulus goes to zero as the deformation parameter s approaches a critical value sc. We find that when the deformation parameter s is taken sufficiently close to the critical value, inflation lasts more than 60 e-folds even if the initial point of the inflaton allows an O(0.1) deviation in Planck units from the Dall'Agata-Inverso critical point. It turns out that the spectral index ns of the curvature perturbation at the time of the 60 e-folding number is always about 0.96 and within the 1σ range ns=0.9639±0.0047 obtained by Planck, irrespective of the value of the η parameter at the critical saddle point. The tensor-scalar ratio predicted by this model is around 10−3 and is close to the value in the Starobinsky model.

Post-Newtonian constraints on Lorentz-violating gravity theories with a MOND phenomenology

We study the post-Newtonian expansion of a class of Lorentz-violating gravity theories that reduce to khronometric theory (i.e. the infrared limit of Horava gravity) in high-acceleration regimes, and reproduce the phenomenology of the modified Newtonian dynamics (MOND) in the low-acceleration, non-relativistic limit. Like in khronometric theory, Lorentz symmetry is violated in these theories by introducing a dynamical scalar field (the "khronon") whose gradient is enforced to be timelike. As a result, hypersurfaces of constant khronon define a preferred foliation of the spacetime, and the khronon can be thought of as a physical absolute time. The MOND phenomenology arises as a result of the presence, in the action, of terms depending on the acceleration of the congruence orthogonal to the preferred foliation. We find that if the theory is forced to reduce exactly to General Relativity (rather than to khronometric theory) in the high-acceleration regime, the post-Newtonian expansion breaks down at low accelerations, and the theory becomes strongly coupled. Nevertheless, we identify a sizeable region of the parameter space where the post-Newtonian expansion remains perturbative for all accelerations, and the theory passes both solar-system and pulsar gravity tests, besides producing a MOND phenomenology for the rotation curves of galaxies. We illustrate this explicitly with a toy model of a system containing only baryonic matter but no Dark Matter.

Interacting modified QCD ghost scalar field models of dark energy

The interacting framework of modified QCD ghost dark energy with cold dark matter is being considered for illustrating the accelerated expansion of the universe. We develop the Hubble parameter numerically and find that it shows increasing behavior which is consistent with the present observations. Also, the equation state parameter shows evolution of the universe from matter dominated universe towards phantom era by evolving the quintessence as well as vacuum eras of the universe. The dynamics of scalar field and corresponding potential of various scalar field models shows consistence behavior with the accelerated expansion phenomenon. Also, the kinetic energy term of k-essence and dilaton models lies within the range where equation of state parameter represents the accelerated expansion of the universe.

Bounce universe from string-inspired Gauss-Bonnet gravity

We explore cosmology with a bounce in Gauss-Bonnet gravity where the Gauss-Bonnet invariant couples to a dynamical scalar field. In particular, the potential and and Gauss-Bonnet coupling function of the scalar field are reconstructed so that the cosmological bounce can be realized in the case that the scale factor has hyperbolic and exponential forms. Furthermore, we examine the relation between the bounce in the string (Jordan) and Einstein frames by using the conformal transformation between these conformal frames. It is shown that in general, the property of the bounce point in the string frame changes after the frame is moved to the Einstein frame. Moreover, it is found that at the point in the Einstein frame corresponding to the point of the cosmological bounce in the string frame, the second derivative of the scale factor has an extreme value. In addition, it is demonstrated that at the time of the cosmological bounce in the Einstein frame, there is the Gauss-Bonnet coupling function of the scalar field, although it does not exist in the string frame.

Polymer inflation

We consider the semi-classical dynamics of a free massive scalar field in a homogeneous and isotropic cosmological spacetime. The scalar field is quantized using the polymer quantization method assuming that it is described by a gaussian coherent state. For quadratic potentials, the semi-classical equations of motion yield a universe that has an early "polymer inflation" phase which is generic and almost exactly de Sitter, followed by a epoch of slow-roll inflation. We compute polymer corrections to the slow roll formalism, and discuss the probability of inflation in this model using a physical Hamiltonian arising from time gauge fixing. We also show how in this model, it is possible to obtain a significant amount of slow-roll inflation from sub-Planckain initial data, hence circumventing some of the criticisms of standard scenarios. These results show the extent to which a quantum gravity motivated quantization method affects early universe dynamics.

Ambiguity in running spectral index with an extra light field during inflation

At the beginning of inflation there could be extra dynamical scalar fields that will soon disappear (become static) before the end of inflation. In the light of multi-field inflation, those extra degrees of freedom may alter the time-dependence of the original spectrum of the curvature perturbation. It is possible to remove such fields introducing extra number of e-foldings prior to 0Ne∼ 6, however such extra e-foldings may make the trans-Planckian problem worse due to the Lyth bound. We show that such extra scalar fields can change the running of the spectral index to give correction of ± 0.01 without adding significant contribution to the spectral index. The corrections to the spectral index (and the amplitude) could be important in considering global behavior of the corrected spectrum, although they can be neglected in the estimation of the spectrum and its spectral index at the pivot scale. The ambiguity in the running of the spectral index, which could be due to such fields, can be used to nullify tension between BICEP2 and Planck experiments.

Correspondence of pilgrim dark energy with scalar field models

In this paper, we consider interacting pilgrim dark energy (Hubble horizon as an infrared cutoff) with cold dark matter in flat universe. We develop the equation of state parameter in this scenario which shows the consistency with pilgrim dark energy phenomenon. In this framework, we analyze the behavior of scalar field and corresponding scalar potentials (which describe the dynamics of the scalar fields) of various scalar field models, graphically. The dynamics of scalar fields and potentials indicate accelerated expansion of the universe which is consistent with the current observations.

Holography as a gauge phenomenon in Higher Spin duality

Employing the world line spinning particle picture. We discuss the appearance of several different ‘gauges’ which we use to gain a deeper explanation of the Collective/Gravity identification. We discuss transformations and algebraic equivalences between them. For a bulk identification we develop a ‘gauge independent’ representation where all gauge constraints are eliminated. This ‘gauge reduction’ of Higher Spin Gravity demonstrates that the physical content of 4D AdS HS theory is represented by the dynamics of an unconstrained scalar field in 6d. It is in this gauge reduced form that HS Theory can be seen to be equivalent to a 3 + 3 dimensional bi-local collective representation of CFT3.

Quasi Stable Solitons Generated by Landscape

Based on the landscape idea we consider solitons formation during inflation. We consider special case of scalar field dynamics and discuss characteristics of non-trivial field configurations, obtained in our approach.

Dark Energy coupling with electromagnetism as seen from future low-medium redshift probes

Beyond the standard cosmological model where the late-time accelerated expansion of the universe is driven by a cosmological constant, the observed expansion can be reproduced as well by the introduction of an additional dynamical scalar field. In this case, the field is expected to be naturally coupled to the rest of the theory's fields, unless a (still unknown) symmetry suppresses this coupling. Therefore, this would possibly lead to some observational consequences, such as space-time variations of nature's fundamental constants. In this paper we investigate the coupling between a dynamical Dark Energy model and the electromagnetic field, and the corresponding evolution of the fine structure constant (α) with respect to the standard local value α0.

Angular momentum generation from holographic Chern-Simons models

We study parity-violating effects, particularly the generation of angular momentum density and its relation to the parity-odd and dissipationless transport coefficient Hall viscosity, in strongly-coupled quantum fluid systems in 2+1 dimensions using holographic method. We employ a class of 3+1-dimensional holographic models of Einstein-Maxwell system with gauge and gravitational Chern-Simons terms coupled to a dynamical scalar field. The scalar can condensate and break the parity spontaneously. We find that when the scalar condensates, a non-vanishing angular momentum density and an associated edge current are generated, and they receive contributions from both gauge and gravitational Chern-Simons terms. The angular momentum density does not satisfy a membrane paradigm form because the vector mode fluctuations from which it is calculated are effectively massive. On the other hand, the emergence of Hall viscosity is a consequence of the gravitational Chern-Simons term alone and it has membrane paradigm form. We present both general analytic results and numeric results which take back-reactions into account. The ratio between Hall viscosity and angular momentum density resulting from the gravitational Chern-Simons term has in general a deviation from the universal 1/2 value obtained from field theory and condensed matter physics.

Ghost quintessence in fractal gravity

In this study, using the time-like fractal theory of gravity, we mainly focus on the ghost dark energy model which was recently suggested to explain the present acceleration of the cosmic expansion. Next, we establish a connection between the quintessence scalar field and fractal ghost dark energy density. This correspondence allows us to reconstruct the potential and the dynamics of a fractal canonical scalar field (the fractal quintessence) according to the evolution of ghost dark energy density.

Conformal and non conformal dilaton gravity

The quantum dynamics of the gravitational field non-minimally coupled to an (also dynamical) scalar field is studied in the {\em broken phase}. For a particular value of the coupling the system is classically conformal, and can actually be understood as the group averaging of Einstein-Hilbert's action under conformal transformations. Conformal invariance implies a simple Ward identity asserting that the trace of the equation of motion for the graviton is the equation of motion of the scalar field. We perform an explicit one-loop computation to show that the DeWitt effective action is not UV divergent {\em on shell} and to find that the Weyl symmetry Ward identity is preserved {\em on shell} at that level. We also discuss the fate of this Ward identity at the two-loop level --under the assumption that the two-loop UV divergent part of the effective action can be retrieved from the Goroff-Sagnotti counterterm-- and show that its preservation in the renormalized theory requires the introduction of counterterms which exhibit a logarithmic dependence on the dilaton field.

Fluctuations of cosmological birefringence and the effect on CMBB-mode polarization

The cosmological birefringence caused by the coupling between the cosmic scalar field and the cosmic microwave background (CMB) photons through the Chern-Simons term can rotate the polarization planes of the photons, and mix the CMB E-mode and B-mode polarizations. The rotation angle induced by the dynamical scalar field can be separated into the isotropic background part and the anisotropic fluctuations. The effect of the background part has been be studied in the previous work (Zhao & Li, arXiv:1402.4324). In this paper, we focus on the influence of the anisotropies of the rotation angle. We first assume that the cosmic scalar field is massless, consistent with other works, we find that the rotation spectrum can be quite large, which may be detected by the potential CMB observations. However, if the scalar field is identified as the quintessence field, by detailed discussing both the entropy and adiabatic perturbation modes for the first time, we find that the anisotropies of the rotation angle are always too small to be detectable.In addition, as the main goal of this paper, we investigate the effect of rotated polarization power spectrum on the detection of relic gravitational waves. we find that, the rotated B-mode polarization could be fairly large, and comparable with those generated by the gravitational waves. This forms a new contamination for the detection of relic gravitational waves in the CMB. In particular, we also propose the method to reconstruct and subtract the rotated B-mode polarization, by which the residuals become negligible for the gravitational-wave detection.

A Model for Staircase Formation in Fingering Convection

Fingering convection is a convective instability that occurs in fluids where two buoyancy-changing scalars with different diffusivities have a competing effect on density. The peculiarity of this form of convection is that, although the transport of each individual scalar occurs down-gradient, the net density transport is up-gradient. In a suitable range of non-dimensional parameters, solutions characterized by constant vertical gradients of the horizontally averaged fields may undergo a further instability, which results in the alternation of layers where density is roughly homogeneous with layers where there are steep vertical density gradients, a pattern known as "doubly-diffusive staircases". This instability has been interpreted in terms of an effective negative diffusivity, but simplistic parameterizations based on this idea, obviously, lead to ill-posed equations. Here we propose a mathematical model that describes the dynamics of the horizontally-averaged scalar fields and the staircase-forming instability. The model allows for unstable constant-gradient solutions, but it is free from the ultraviolet catastrophe that characterizes diffusive processes with a negative diffusivity.

Quantum corrections to scalar field dynamics in a slow-roll space-time

We consider the dynamics of a quantum scalar field in the background of a slow-roll inflating Universe. We compute the one-loop quantum corrections to the field and Friedmann equation of motion, in both a 1PI and a 2PI expansion, to leading order in slow-roll. Generalizing the works of [1-3], we then solve these equations to compute the effect on the primordial power spectrum, for the case of a self-interacting inflaton and a self-interacting spectator field. We find that for the inflaton the corrections are negligible due to the smallness of the coupling constant despite the large IR enhancement of the loop contributions. For a curvaton scenario, on the other hand, we find tension in using the 1PI loop corrections, which may indicate that the quantum corrections could be non-perturbatively large in this case, thus requiring resummation.

Dynamics of cosmological scalar fields

The background dynamical evolution of a universe filled with matter and a cosmological scalar field is analyzed employing dynamical system techniques. After the phenomenology of a canonical scalar field with exponential potential is revised, square and square root kinetic corrections to the scalar field canonical Lagrangian are considered and the resulting dynamics at cosmological distances is obtained and studied. These noncanonical cosmological models imply new interesting phenomenology including early time matter dominated solutions, cosmological scaling solutions and late time phantom dominated solutions with dynamical crossing of the phantom barrier. Stability and viability issues for these scalar fields are presented and discussed.

Dark energy coupling with electromagnetism as seen from future low-medium redshift probes

Beyond the standard cosmological model the late-time accelerated expansion of the universe can be reproduced by the introduction of an additional dynamical scalar field. In this case, the field is expected to be naturally coupled to the rest of the theory's fields, unless a (still unknown) symmetry suppresses this coupling. Therefore, this would possibly lead to some observational consequences, such as space-time variations of nature's fundamental constants. In this paper we investigate the coupling between a dynamical Dark Energy model and the electromagnetic field, and the corresponding evolution of the fine structure constant ($\alpha$) with respect to the standard local value $\alpha_0$. In particular, we derive joint constraints on two dynamical Dark Energy model parametrizations (the Chevallier-Polarski-Linder and Early Dark Energy model) and on the coupling with electromagnetism $\zeta$, forecasting future low-medium redshift observations. We combine supernovae and weak lensing measurements from the Euclid experiment with high-resolution spectroscopy measurements of fundamental couplings and the redshift drift from the European Extremely Large Telescope, highlighting the contribution of each probe. Moreover, we also consider the case where the field driving the $\alpha$ evolution is not the one responsible for cosmic acceleration and investigate how future observations can constrain this scenario.