1. Introduction
In hydrodynamic turbulence, dissipation of energy is in principle straightforward: everything that gets in through forcing does get out eventually; see
Figure 1. But when magnetic fields are involved, energy can be transferred from kinetic energy to magnetic by doing work against the Lorentz force,
. In that case, the situation is more complicated, because there are now two exit channels, and it is
a priori not clear, which of the two takes the lion’s share in specific situations; see
Figure 2. A related problem may also occur when the electric energy reservoir is involved, and especially when this energy reservoir is later absent due to high conductivity. Before getting to that, let us first recall the different situations in hydrodynamic and hydromagnetic turbulence.
Figure 2 presumes that kinetic energy can be tapped by dynamo action and converted into magnetic energy [
1]. This is a generic process that we now know works in virtually all types of turbulent systems provided the electric conductivity is large enough [
2]. And here comes already the first problem. Large conductivity means small magnetic diffusivity and therefore also less dissipation [
3]. Looking at
Figure 2 however, this seems puzzling: In the steady state, the dynamo term
must be just as large as the resistive term,
ϵM. Thus, if the dynamo is efficient, also the dissipation must be large, which is not expected (and also not true).
The puzzle of efficient dynamo action, but inefficient dissipation was solved by realizing that at large conductivity (and especially large magnetic Prandtl number, which is the ratio Pr
M of kinematic viscosity
to magnetic diffusivity
, is much larger than unity), a second conversion occurs at smaller length scales where magnetic energy can be converted back into kinetic energy. This process was termed a reversed dynamo [
4], and it happens at small scales when Pr
M . The concept of a reversed dynamo was already introduced previously [
5] in the context of large-scale dynamos leading to the formation of large-scale flows driven with the large-scale field by microscopic fields and flows, but in the context of Ref. [
4], the focus was on small-scale dynamos that drive small-scale flows by the Lorentz force when Pr
M .
While the conversion between magnetic and kinetic energies is reasonably well understood, not much is known about the conversion from electromagnetic energy, i.e., the sum of electric and magnetic energies, into magnetic energy when the electric conductivity gradually increases. Such a process is important at the end of cosmological inflation [
6]. A stochastic electromagnetic field may have been produced during inflation and reheating [
7]. At the end of reheating, the electric conductivity of the universe increased. As discussed in Ref. [
8], significant magnetic field losses can occur if the increase of conductivity takes very long, especially when the magnetic diffusivity is at an intermediate level for a long time. In the two extreme cases of very large diffusivity (corresponding to a vacuum with undamped electromagnetic waves), and very small diffusivity (corresponding to nearly perfect conductivity), no significant losses are expected. It is only during the period when the magnetic diffusivity is at an intermediate level that significant resistive losses can occur.
Once the conductivity has reached large values, i.e., when the magnetic diffusivity is small, strong turbulent flows will be driven. In that regime, the Faraday displacement current can be neglected and the equations reduce to those of magnetohydrodynamics [
9]. The resulting turbulent flows cause the magnetic field to undergo
turbulent decay with inverse cascading, as has been studied intensively since the mid 1990s [
10,
11,
12,
13,
14,
15,
16]. At some point around the time of recombination, the photon mean free path becomes very large and a process called Silk damping becomes important [
17]. It results from the interactions between photons and the gas and damps out all inhomogeneities in the photon–baryon plasma [
18]. In [
19], this was modeled as a strongly increased viscosity, making the magnetic Prandtl number even larger. However, a more physical approach is to add a friction term of the form
on the right hand side of the momentum equation [
12]. It is generally taken for granted that the magnetic fields just survive Silk damping without much additional loss, and that they are just frozen into the plasma. However, the details of this process have not yet been modeled.
The goal here is to understand more quantitatively how much magnetic energy survives during the conversions from electromagnetic fields to magnetohydrodynamic fields as the conductivity increases. We also consider in more detail the conversion from magnetic fields to electric fields at the end of the cosmological reheating phase when both fields are still growing and not yet equal to each other—unlike the situation when electromagnetic waves are present, and there is no growth anymore.
2. Energetics during the emergence of conductivity
The evolution of the electric and magnetic fields,
E and
B, respectively, is given by the Maxwell equations, written here in SI units:
where
c is the speed of light and
is the vacuum permeability. To close the equations, we use Ohm’s law,
where
is the electric conductivity and is the velocity.
In the very early Universe, inflation dilutes the plasma to the extent that there are virtually no particles, and hence the electric conductivity vanishes. Eventually, a phase of reheating must have occurred. One possibility is that the stretching associated with the cosmological expansion leads to electromagnetic field amplification until the electric field begins to exceed the critical field strength for the Schwinger effect [
20] to lead to the production of charged particles, and thereby to the emergence of electric conductivity. This change in
implies the existence of a phase when
has an intermediate value for a certain duration. This leads to a certain electromagnetic energy loss given by
J ·
E. This is a well-known result in magnetohydrodynamics, where the displacement current is ignored, so we have
. This is then used when deriving the magnetic energy equation by taking the dot product of Equation (2) with
B, so we have
where we have introduced the Poynting vector
, but since a divergence under triply-periodic volume averaging vanishes, we just have
The <
J ·
E> term, in turn, has two contributions. Using Ohm’s law in the form
we find
, or, using
, we have
so part of the electromagnetic energy turns into Joule (or magnetic) heating,
ϵM , and another part is converted into kinetic energy through work done by the Lorentz force,
, which eventually also gets converted into heat through viscous (kinetic) heating,
ϵK. In the case of dynamo action discussed in the introduction, of course,
is negative, so work is done
against the Lorentz force. This is why the direction of the arrow in
Figure 2 is reversed.
In the scenario where reheating is caused by the feedback from the Schwinger effect, there would be thermal energy supply both from
ϵK and
ϵM, leading therefore to a direct coupling between the resulting heating and the emergence of
. The flows of energy between magnetic, electric, and kinetic energy reservoirs is illustrated in
Figure 3. We denote those by
respectively. Their evolution equations can be obtained from Eqs. (32) and (2), along with the momentum and continuity equations,
where
is the advective derivative,
is the pressure for an isothermal equation of state with sound speed
cs, which is constant,
is the viscosity, and
are the components of the rate-of-strain tensor
S.
Taking the dot product of Equation (9) with
u, using Equation (10), integration by part, and the facts that
can be written as the sum of a symmetric and an antisymmetric tensor, but that the multiplication with
S (a symmetric and trace-free tensor) gives no contribution when
is added, we find that
, and thus obtain the evolution equation for the kinetic energy is of the form
which we can also write more compactly as
, where
has been defined as the work done by the pressure force,
is the viscous (or kinetic) heating, and the dot on the kinetic energy denotes a time derivative. Here we have made use of the fact that the divergence
has a vanishing volume average for a triply-periodic domain, and therefore
, making it clear that this term leads to compressional heating and was found to be important in gravitational collapse simulations [
21]. We will see later that, when energy is supplied through
, the energy is used to let the kinetic energy grow (
) and to drive viscous heating, i.e., we have
The term
is usually small and negative and thus also contributes (but only little) to increasing thermal energy. In the present simulations, we used an isothermal equation of state and thus ignored the evolution of thermal energy,
, where
is the internal energy,
cv is the specific heat at constant volume, and
T is the temperature. If we had included it, we would have had
This thermal evolution is important in simulations of thermal magneto-convection [
22], where it facilitates buoyancy variations, or in simulations of the magneto-rotational instability, where potential energy gets dissipated into heat and radiation [
23]. For our purposes, however, it suffices to integrate instead the kinetic and magnetic contributions in time, i.e., to compute
and
, respectively.
Let us now discuss the interplay between electric and magnetic energies. This interplay is usually ignored in magnetohydrodynamics, where the evolution of the electric field, i.e., the Faraday displacement current, is ignored [
9]. Taking the dot product of Equation (32) with
and noting that
is the vacuum permittivity, we obtain
so, after averaging, we have
Next, taking the dot product of Equation (2) with
, we obtain
In view of the
term in Equation (15), it is convenient to rewrite Equation (16) in the form
Again, given that the Poynting flux divergence vanishes under a triply-periodic volume averaging, we have
More compactly, we can then write , where acts as a source in . Thus, we clearly see that the electric energy reservoir is not a secondary one whose energy content is small because of inefficient coupling, but it is an unavoidable intermediate one through which magnetic energy gets channeled efficiently further to kinetic and thermal energies. This raises the question how safe in the neglect of the displacement current when prior to the emergence of conductivity, the electric energy dominates over magnetic. This is a typical situation in inflationary magnetohydrodynamics scenarios that we consider later in this paper. Before that, we discussed first the standard case when electric and magnetic energies are equally large.
4. Cosmological application prior to radiation domination
As alluded to above, the end of inflation might provide an opportunity to illustrate electromagnetic energy conversion, because in that case, the electric energy can greatly exceed the magnetic one.
4.1. Magnetic fields in cosmology
In the present Universe, magnetic fields are constantly being regenerated by dynamo action on all scales up to those of galaxy clusters. The energy source is here gravitational, which is released through accretion or direct collapse. Magnetic fields may also be present on even larger scales. However, in the locations between galaxy clusters, i.e., in what is often referred to as voids, it is generally thought impossible to produce magnetic fields through contemporary dynamo action; see Refs. [
26,
27] for reviews on the subject. Nevertheless, indirect evidence for the existence of magnetic fields in voids, and more specifically for lower limits of the magnetic field strength, comes from the non-observation of secondary photons in the halos to blazars, which are active galactic nuclei producing TeV photons. These photons interact with those of the extragalactic background light through inverse Compton scattering to produce GeV photons. Those secondary GeV photons are not observed. Their non-observation could be explained by an intervening magnetic field of about
on a megaparsec scale [
28,
29]. This field would deflect electrons and positrons in opposite directions, preventing them from recombining and thereby disrupting the energy cascade toward the lower GeV photons.
The non-observation of GeV photons might have other reasons, for example plasma instabilities that disrupt the electron–positron beam [
30,
31]. Nevertheless, even then, a certain fraction of the plasma beam disruption might still be caused by magnetic fields [
32], which could explain the GeV halos of at least some blazars [
33]. If magnetic fields really do exist on very large cosmological scales, they may be primordial in origin. This may mean that they have been created during or before the radiation-dominated era of the Universe, for example during one of the cosmological phase transitions or during inflation. Inflation was a phase where the conversion from electromagnetic fields to magnetohydrodynamic fields played an important role, which is what we are interested in here.
4.2. Use of comoving variables and conformal time
The universe is expanding with time, as described by the scale factor
. The equations of magnetohydrodynamics therefore contain additional terms with factors of
and its time derivatives. However, by using scaled variables,
,
,
,
,
, along with conformal time,
, all
factors and other terms involving
disappear from the magnetohydrodynamic equations [
10]. The velocity is the same in both frames, i.e.,
.
Given that the equations with tilded variables are equal to the ordinary ones in a non-expanded Universe, it is convenient to skip all tildes from now on. However, when discussing the evolution of the scale factor, for example, we do need again physical time, which will then be denoted by , while t then still denotes conformal time. Here is where we have a notational dilemma, because in cosmology, derivatives with respect to physical (or cosmic) time are often denoted by dots, while those with respect to conformal time are denoted by primes. We therefore decided here to follow the same convention, so and denote derivatives with respect to conformal time.
4.3. Inflationary magnetogenesis
Inflationary magnetogenesis models assume the breaking of conformal invariance through a factor
in the electric energy contribution to the Lagrangian density
, where
is the Faraday tensor [
34]. Early approaches to inflationary magnetogenesis exposed specific problems: the strong coupling and the backreaction problems [
35], as well as the Schwinger effect constraint, which can lead to a premature increase in the electric conductivity. This shorts the electric field and prevents further magnetic field growth [
20]. This is particularly important for models that solve the backreaction problem by choosing a low energy scale inflation [
36], but could be avoided if charged particles get sufficiently large masses by some mechanism in the early Universe [
37]. The three problems are avoided by requiring the function
f to obey certain constraints [
7,
38].
Successful models of inflationary magnetogenesis are thus possible, but this does not mean that the underlying cosmological models are also physically preferred options. Nevertheless, for the purpose of discussing the electromagnetic energy conversion, which is the goal of this paper, those models are a useful choice.
Three-dimensional simulations of inflationary magnetogenesis have been performed by assuming an abrupt switch from electromagnetism without currents and magnetohydrodynamics where the displacement current is already neglected [
8,
39]. They solved the evolution equations for the scaled magnetic vector potential,
, in the Coulomb gauge:
where
is a generation term, because it destabilizes the field at large length scales for wave numbers
. Analogous to the primes on
, primes on
also denote conformal time derivatives. Towards the end of the reheating phase, where
, we expect
.
Our aim here is to present calculations where the transit from vacuum to high conductivity is continuous. In particular, to calculate the generation term
, one commonly uses a power law representation in terms of
of the form
with
during inflation and
with
during reheating [
40]. We are here only interested in the reheating phase where
[
7,
38] such that it is unity when the radiation-dominated era begins, and therefore
and
for
. For
, by contrast, we have
Note that for , we have and , so and , and therefore .
Contrary to the earlier numerical work [
8,
39], the displacement current is now included at all times. However, there is still a problem in that
has a discontinuity from
to zero at the moment when the conductivity is turned on. In the simulations, this did not seem to have any serious effect on the results, because the magnetic field at the end of the electromagnetic phase only acted as an initial condition for the magnetohydrodynamic calculation after the switch. In a continuous calculation without switch, however, this problem must be avoided. This will be addressed next.
4.4. Continuous version of the generation term
An instructive way of obtaining a smooth transition from a quadratic to a linear growth profile of
is obtained by solving the Friedmann equations for a piecewise constant equation of state,
, which relates the pressure with the density through
. Under the assumption of zero curvature, i.e., the Universe is conformally flat, but expanding, the Friedmann equations can be written as a single equation which, in physical time, takes the form
where
is the standard Hubble parameter. Here,
during the radiation-dominated era and
during reheating when there were no photons, which is there equivalent to the matter-dominated era that also occurs later after recombination and before the Universe began to accelerate again. The accelerated exponential expansion of the universe during inflation, and also the late acceleration of the present Universe, correspond to
, but this will not be considered in the present paper.
It is convenient to solve the Friedmann equation with zero curvature in conformal time. It then takes the form
, where
is the conformal Hubble parameter. It is related to the usual one,
H, through
. Note the opposite sign of the terms on the right-hand side and the opposite sign in front of
compared to the formulation in terms of physical time. The equation for
is easily solved by splitting it into two first-order equations and introducing a new variable
and solving for
see also Ref. [
41] for similar work in another context.
Figure 10 shows the solution for
and the ratios
and
compensated by
t and
, respectively, which allows us to see more clearly how
changes from
to
and
changes from
to zero as we go from the reheating era to the radiation-dominated universe after reheating.
What is important here is the generation term
. It determines the wave number below which the solution is still unstable. However, since
, we have
; see
Table 2. In
Figure 11, we plot the evolution
ƐE,
ƐM, and
ƐK for
for all three values of
: 1, 2, and 4. Here and below, the initial amplitudes have been arranged such that
ƐM at
. In all cases, the solution has become stable by the time
, and we see electromagnetic oscillations toward the end of the reheating phase before conductivity turns on at
. This is here referred to as Set (i).
It is easy to see that on large length scales, when the
operator in Equation (25) is negligible compared with
, we have
Thus, for , corresponding to super-horizon scales, where and when the modes are still unstable, we have . On smaller length, scales, i.e., for larger k values, the modes become stable and we have the usual electromagnetic waves.
When modeling the transition from a vacuum to that of high conductivity and the corresponding Joule heating, we still need to make a choice as to when
would begin to increase, i.e., we need to choose values of
and
. If we choose the value of
to be too large, we obtain solutions where electromagnetic waves have already been established; see
Figure 11. The smallest wavenumber in our one-dimensional domain is
, so by the time
, even the largest modes in the domain are stable. We also see that at early times,
ƐE and
ƐM grow in an algebraic fashion and then become oscillatory when
has dropped below
k. At
, when conductivity turns on, the electric energy decreases rapidly, while the magnetic energy diminishes only very slowly. The generated hydrodynamic energy is however small. This is similar to what we studied in
Section 3.2.
Our objective here is to study cases that are different from what was studied in
Section 3.2. Therefore we now choose Set (ii) with
and
(
Figure 12) and another Set (iii) with
and
(
Figure 13). Again, the electric energy drops significantly when conductivity turns on, but now there is a much larger spread in the resulting maximum magnetic energies for the three cases with
, 2, and 4. For
,
K reaches about one percent of
M at
, for example.
When increasing the wavenumber to
, the largest modes are still unstable for the three cases with
, 2, and 4; see
Figure 13. Here,
and
and
. The spread in the magnetic energy is similar, but the maximum kinetic energy is now much larger; see
Table 3.
4.5. Energy conversions during reheating
During reheating, there is an additional source of energy resulting from the generation term
. The term
appeared in Equation (25) for
. However, to write down the relevant equation for
, we have to revert to the original equation for
A, which reads [
40]
Thus, Eq. (32) with the current density term restored, now becomes
and therefore, Eq. (15) for the electric energy now has an extra term and reads
During reheating with
, we have
, so the first term on the right-hand side of dE2dt3 is positive. Similarly to what was done in Section 3.2, we can write the electric energy equation more compactly as
, where
is now the dominant source, but
plays here the role of a sink during the first part of the evolution. This equation generalizes epsMeqn to the case with electromagnetic field generation during reheating; see also
Figure 14.
The evolution of
,
,
, and ϵ
M is shown in
Figure 15 during magnetic field generation in the case (ii) for all three values of
. It is instructive to write the electric energy equation as
Comparing the three panels of
Figure 15, we thus see that for
, there is a slow generation phase starting much before
. It should be noted, however, that the ranges on the vertical axis are different for the different panels.
At , there is a rise of conductivity, and therefore a sharp rise in Ohmic heating, ϵM. This is also the time when reaches a maximum and becomes negative shortly thereafter. For large values of , this moment happens a bit later, at compared to for . Note that, while for the maxima of and ϵM are similar, for smaller values of , the maxima of ϵM are much larger than those of . Instead, for , for example, we have , i.e., almost the entire heating is here caused by dissipation of electric energy.
In
Figure 16, we show a plot similar to
Figure 15, but for the case (i), where all modes were already oscillatory at
, when conductivity turned on. The Ohmic heating now plays a minor role in the sense that its maximum value is much less than the extrema of
,
, and
. For
and 2, we see that
and
are nearly in phase shortly before conductivity turns on. This means that the electric and magnetic energies are strongly coupled and a flow of energy from magnetic to electric energy (
) leads to an increase of electric energy (
). This is expected, because there is just an oscillatory exchange between electric and magnetic energies. For
, on the other hand, the oscillatory phase just started to develop shortly before
, but the curves are similar to those for
and 2, although at earlier times. The time of the first maximum of
is at
for
, while for
, it is at
and for
it is at
, and we see that the profiles of all curves are indeed very similar around those times.
5. Conclusions
In this paper, we have studied the conversion of electromagnetic energy into kinetic and thermal energies as the electric conductivity transits from zero (vacuum) to large values. This problem has relevance to the reheating phase at the end of cosmological inflation and before the emergence of an extended, radiation-dominated era before the time of recommendation, which is much later. While not much is known about the physical processes leading to reheating and the emergence of conductivity, a lot can now be said about the general process of such an energy conversion.
Already in the absence of cosmological expansion, we have seen that the transition to conductivity involves an oscillatory exchange between electric and magnetic energies. It is mainly the electric energy reservoir that delivers energy to the kinetic and thermal energy reservoirs, and not magnetic energy directly, as in magnetohydrodynamics. We knew already from earlier work that the duration of the transit plays a significant role in causing a drop in magnetic energy. We now also see that this drop depends on the magnetic field strength and thus the typical Alfvén speed. The drop can become small if the Alfvén speed becomes comparable to the speed of light. Furthermore, for short transits, we have seen that energy transfer between electric and magnetic energies is small and that the initial electric energy goes directly into thermal energy. For longer transits, however, the mutual exchange with magnetic energy becomes approximately equal to the thermal energy loss, so thermalization now also involves the magnetic energy reservoir.
When applying electromagnetic energy conservation to the problem of reheating, we have a new quality in the model in that there is now also energy transfer through conformal invariance breaking, which may occur during inflation and reheating. This is obviously speculative, but a very promising scenario for the generation of large-scale magnetic fields in the early Universe [
34] and for explaining the observed lower limits of the intergalactic magnetic field on megaparsec length scales [
28,
29].
The present study has shown that significant work can be done by the Lorentz force when the electromagnetic energy conversion happens early and on scales large enough so that the modes are still growing in time. This is because there is then significant excess of electric energy over magnetic. This is an effect that was ignored in previous simulations of inflationary magnetogenesis and, in particular, the resulting relic gravitational wave production [
8,
39].
It will be useful to extend these studies to turbulent flows and magnetic fields, but this is not easy because of numerical and perhaps even physical instabilities. Once these problems are overcome, it would also be interesting to study dynamo action in situations of moderate magnetic conductivity where coupling with the electric energy reservoir could reveal new aspects. We leave this for future work.
Figure 1.
Kinetic energy dissipation, ϵK, of forced turbulence with kinetic energy density , where is the density and u is the velocity: in the steady state, everything that gets in does get out.
Figure 1.
Kinetic energy dissipation, ϵK, of forced turbulence with kinetic energy density , where is the density and u is the velocity: in the steady state, everything that gets in does get out.
Figure 2.
Dissipation in dynamos: there are now two exit channels, ϵK and ϵM, and it is not clear who takes the lion’s share. Dynamo action corresponds to (work done against the Lorentz force), although energy can also go the other way around when an initial magnetic field decays.
Figure 2.
Dissipation in dynamos: there are now two exit channels, ϵK and ϵM, and it is not clear who takes the lion’s share. Dynamo action corresponds to (work done against the Lorentz force), although energy can also go the other way around when an initial magnetic field decays.
Figure 3.
Energy conversion from magnetic to kinetic energies via the electric energy reservoir.
Figure 3.
Energy conversion from magnetic to kinetic energies via the electric energy reservoir.
Figure 4.
Evolution of for the logarithmic profile with (a) , (b) , and (c) , and in all cases.
Figure 4.
Evolution of for the logarithmic profile with (a) , (b) , and (c) , and in all cases.
Figure 5.
Evolution of for the logarithmic profile with and (a) the logarithmic profile with , (b) the linear profile with , and (c) the linear profile with .
Figure 5.
Evolution of for the logarithmic profile with and (a) the logarithmic profile with , (b) the linear profile with , and (c) the linear profile with .
Figure 6.
(a) Evolution of
at one specific point
in the three runs of
Figure 5a,c. Note that the drop of the wave amplitude after
is similar for runs
a and
c, but much less for
b. (b) Dependence of
for the logarithmic profile with
in run
a, and the linear profile with
in run
b and
in run
c. We see from the inset of panel
b that the time spent in
traversing unity by a margin of one order of magnitude is similar for
a and
c, but virtually non-existing for
b.
Figure 6.
(a) Evolution of
at one specific point
in the three runs of
Figure 5a,c. Note that the drop of the wave amplitude after
is similar for runs
a and
c, but much less for
b. (b) Dependence of
for the logarithmic profile with
in run
a, and the linear profile with
in run
b and
in run
c. We see from the inset of panel
b that the time spent in
traversing unity by a margin of one order of magnitude is similar for
a and
c, but virtually non-existing for
b.
Figure 7.
Initially, all the energy is in electromagnetic energy, E + M for and . In the end, all the energy gets converted into heat. The red lines give the integrated Ohmic and viscous energy gains, and , respectively. At intermediate times, this energy gets distributed to equal amounts to kinetic energy, K and magnetic energy M. The orange line shows K + M. The yellow and blue lines give just E and K separately.
Figure 7.
Initially, all the energy is in electromagnetic energy, E + M for and . In the end, all the energy gets converted into heat. The red lines give the integrated Ohmic and viscous energy gains, and , respectively. At intermediate times, this energy gets distributed to equal amounts to kinetic energy, K and magnetic energy M. The orange line shows K + M. The yellow and blue lines give just E and K separately.
Figure 8.
Evolution of energy fluxes for the model with the ’log-switch-on’ conductivity profile. . In all cases, the initial diffusivity is . The only difference to the run with a larger viscosity is that ϵK is larger.
Figure 8.
Evolution of energy fluxes for the model with the ’log-switch-on’ conductivity profile. . In all cases, the initial diffusivity is . The only difference to the run with a larger viscosity is that ϵK is larger.
Figure 9.
M at , i.e., after the conductivity has increased to large value, vs for (orange), (red), and (blue).
Figure 9.
M at , i.e., after the conductivity has increased to large value, vs for (orange), (red), and (blue).
Figure 10.
t dependence of (a) the scale factor , (b) the compensated Hubble coefficient , and (c) the compensated left-hand side of the Friedmann equation, . In (a), the asymptotic dependences and for and are overplotted as dashed-dotted orange lines. In (c), the function is overplotted as a dotted red line.
Figure 10.
t dependence of (a) the scale factor , (b) the compensated Hubble coefficient , and (c) the compensated left-hand side of the Friedmann equation, . In (a), the asymptotic dependences and for and are overplotted as dashed-dotted orange lines. In (c), the function is overplotted as a dotted red line.
Figure 11.
t dependence of (red), (blue), and (green) for runs with (dotted lines), 2 (dashed lines), and 4 (solid lines) for Set (i) with , , and . The initial amplitudes have been arranged such that at .
Figure 11.
t dependence of (red), (blue), and (green) for runs with (dotted lines), 2 (dashed lines), and 4 (solid lines) for Set (i) with , , and . The initial amplitudes have been arranged such that at .
Figure 12.
Similarly to
Figure 11, but for Set (ii) with
,
, and
.
Figure 12.
Similarly to
Figure 11, but for Set (ii) with
,
, and
.
Figure 13.
Similarly to
Figure 11, but for for Set (iii) with
,
, and
.
Figure 13.
Similarly to
Figure 11, but for for Set (iii) with
,
, and
.
Figure 14.
Similar to
Figure 3, but now with inflationary magnetogenesis energy generation and energy exchange between electric and magnetic energies in both directions.
Figure 14.
Similar to
Figure 3, but now with inflationary magnetogenesis energy generation and energy exchange between electric and magnetic energies in both directions.
Figure 15.
t dependence of
(red),
(green), ϵ
M (black),
(blue), and
(orange) for the runs of Set (ii) in
Figure 12 with
and
.
Figure 15.
t dependence of
(red),
(green), ϵ
M (black),
(blue), and
(orange) for the runs of Set (ii) in
Figure 12 with
and
.
Figure 16.
Similarly to
Figure 15, but for the runs of Set (i) in
Figure 11 with
and
. Note that
and
vary in anti-phase.
Figure 16.
Similarly to
Figure 15, but for the runs of Set (i) in
Figure 11 with
and
. Note that
and
vary in anti-phase.
Table 2.
Parameters relevant for the models with different values of .
Table 2.
Parameters relevant for the models with different values of .
|
|
|
|
1 |
3 |
2.5 |
2.45 |
2 |
5 |
4.5 |
4.47 |
4 |
9 |
8.5 |
8.49 |
Table 3.
Summary of various extrema for each of the three sets of models and values of .
Table 3.
Summary of various extrema for each of the three sets of models and values of .
Set |
k |
|
variable |
|
|
|
(i) |
10 |
1 |
|
|
|
|
(ii) |
10 |
0.1 |
|
|
|
|
(iii) |
1 |
1 |
|
|
|
|
(i) |
10 |
1 |
|
|
|
|
(ii) |
10 |
0.1 |
|
|
|
|
(iii) |
1 |
1 |
|
|
|
|
(i) |
10 |
1 |
|
|
|
|
(ii) |
10 |
0.1 |
|
|
|
|
(iii) |
1 |
1 |
|
|
|
|
(i) |
10 |
1 |
|
|
|
|
(ii) |
10 |
0.1 |
|
|
|
|
(iii) |
1 |
1 |
|
|
|
|
(i) |
10 |
1 |
|
|
|
|
(ii) |
10 |
0.1 |
|
|
|
|
(iii) |
1 |
1 |
|
|
|
|
(i) |
10 |
1 |
max |
|
|
|
(ii) |
10 |
0.1 |
|
|
|
|
(iii) |
1 |
1 |
|
|
|
|
(i) |
10 |
1 |
|
|
|
|
(ii) |
10 |
0.1 |
|
|
|
|
(iii) |
1 |
1 |
|
|
|
|
(i) |
10 |
1 |
|
|
|
|
(ii) |
10 |
0.1 |
|
|
|
|
(iii) |
1 |
1 |
|
|
|
|