Horava-Lifshitz early universe phase transition beyond detailed balance

0.24 MB·English

by  F. Kheyri

Horava-Lifshitz early universe phase transition beyond
detailed balance
F. Kheyri∗, M. Khodadi† and H. R. Sepangi‡
Department of Physics, Shahid Beheshti University,Evin, Tehran 19839, Iran
January 29, 2013
3
1
0 Abstract
2
The early universe is believed to have undergone a QCD phase transition to hadrons at about 10µs
n
after the big bang. We study such a transition in the context of the non-detailed balance Horava-Lifshitz
a
theory by investigating the effects of the dynamical coupling constant λ in a flat universe. The evolution
J
of the relevant physical quantities, namely the energy density ρ, temperature T, scale factor a and the
7
Hubble parameter H is investigated before, during and after the phase transition, assumed to be of first
2
order. Also, in view of the recent lattice QCD simulations data, we study a cross-over phase transition of

] theearly universewhose results are based on two different sets of lattice data.
c
q
- 1 Introduction
r
g
[ Recently,apower-counting,ultra-violet(UV)renormalizablequantumgravitytheoryhasbeenproposed[1,2],

2 stirring a considerable amount of interest in its wake. This theory is principally based on a scalar field theory
v introducedbyLifshitz [3]to explainquantumcriticalphenomenonincondensedmatter physics. Inthis theory
0 the action is scale-invariantunder the transformations
6
4 t ℓzt, xi ℓxi, (1)
5 → →
.
1 with z = 2, where z represents the dynamical critical exponent. However, the theory proposed by Horava
0 has the scaling dimension z = 3 and is often referred as Horava-Lifshitz (HL) gravity and is fundamentally
3
non-relativistic. This theory does not have the full diffeomorphism invariance of general relativity, admitting
1
onlyalocalGalileaninvariance. Einsteingeneralrelativitymaythenbeconsideredasemergingasaninfra-red
:
v (IR) fixed point. Invariably, such a theory may have interesting ramifications when applied to cosmologyand,
i
X not surprisingly,a greatamountof interesthas been generatedin this regard. In particular,study ofthe early
universe in the context of the HL gravity [5, 4] would represent an interesting area of research. A number
r
a of works have appeared over the past few years studying the early universe in this context. In [4] it was
suggested that the divergence of the speed of light in the UV region may resolve the horizon problem. The
phenomenological implications of the HL theory were addressed in [6]. Black hole solutions and related issues
were studied very actively in [7, 8, 9, 10], some of the theoretical issues and generalizations of the HL model
were discussed in [11, 12, 13, 14, 15]. Needless to say, a myriad of other interesting topics and issues can be
foundintheliterature. Inviewoftheabove,the presentworkisdevotedtothestudyofQCDphasetransition
in the context of HL gravity in the early universe.
According to standard cosmology, as the early universe expanded and cooled, it underwent a series of
symmetry-breaking phase transitions where topological defects may have formed. During its early evolution,
the universeisbelievedto haveundergoneatleasttwophasetransitions. Theelectroweaktheorypredictsthat
atabout100GeV therewasatransitionfromasymmetrichightemperaturephasewithmasslessgaugebosons
to the Higgs phase, where the SU(2) U(1) gauge symmetry is spontaneously broken and all the masses are
×
generated. Thesecondtransition,predictedbyquantumchromodynamics(QCD),isbelievedtohaveoccurred
atatemperatureofabout200MeV wheretherewasatransitionfromaquark-gluonplasmatoaplasmaoflight
hadrons. Ataboutthe sameenergywe expectthat the globalchiralsymmetry ofQCDwith masslessfermions
is spontaneously broken by the formation of a quark pair condensates. The nature of the QCD transition
∗email: f [email protected]
†email: [email protected]
‡email: [email protected]
1
affects our understanding of the evolution of the universe, see [16] for further insight. In a strong first-order
phase transition the quark-gluon plasma supercools before bubbles of hadron gas are formed. These bubbles
grow, collide and merge, during which gravitational waves could be produced [17]. Baryon-enriched nuggets
could remain between the bubbles, contributing to dark matter. The hadronic phase is the initial condition
for nucleosynthesis, so inhomogeneities in this phase could have a strong effect on its development [18].
The nature of the phase transition involved in the early stages of the evolution of the universe has been a
source of some debate. A first order phase transition was the basic assumption under which calculations had
beendone inthe past. However,detailedlattice QCDcalculationsperformedoverthe yearshasnow upsetthe
balanceinfavorofasmoothcrossoverphasetransition. Itisthereforethepurposeofthepresentworktostudy
the formation of hadrons in the early stages of the evolution of the universe based on the assumption that a
smooth crossover phase transition has been responsible. For the sake of clarity and comparison, we have also
performed our calculations based on the assumption of a first order phase transition which we will discuss in
due course.
Fundamental to the study of any phase transition in the early universe is a knowledge of the equation of
state (EoS) which plays an important role in the hot, strongly interacting matter [19, 20] and hydrodynamic
descriptionofheavyioncollisions[21]. Thereareanumberofmodelswheretheequationofstateinafirstorder
phase transition is used for describing the collective flow in heavy ion collisions. However, as was generally
mentionedabove,latticeQCDsuggeststhatthetransitiontothede-confinedphaseisonlyacrossoverone[22].
TheeffectsoftheEoSonallaspectsofthebehaviorofthesystemunderstudyisthereforeofgreatimportance.
For example, it is not obvious to what extent the collective flow is sensitive to details of the equation of state.
Itisnowwellknownthatinanidealfluiddynamicsscenario,theanisotropyoftheprotonflowismostsensitive
to the QCD equation of state [23].
ManyattemptshavebeenmadeinthelasttwodecadestocalculatetheEoSonalattice,see[24,25]. Lattice
calculations are usually done at finite temperatures andat fixed temporal extent N where the temperature is
τ
changedby varyingthe latticespacinga, T =1/N a. The thermodynamicobservablesarecalculatedthrough
τ
the calculation of the trace of the energy momentum tensor (ǫ 3p), known as trace anomaly, which can be
−
done in the high temperature region rather accurately which is not the case in the low temperature region.
Some authors have studied an analysis of the trace anomaly within the Hadron Resonance Gas model (HRG)
[26]. Such studies show that to reproduce the lattice results for the asqtad and p4 actions of the hotQCD
collaboration, it is mandatory to distort the resonance spectrum away from the physical one, necessary for
taking into account the larger quark masses used in these lattice calculations. So, to construct a realistic
equation of state one could use the lattice data. In a number of works lattice calculations show a reasonably
good agreement with hadron resonance gas (HRG) model predictions at low temperature [27, 28, 29] and in
other works such distortions are not needed to describe the data [42].
Thestartingpointwhenstudyingtheevolutionoftheearlyuniverse,oringeneralanycosmologicalsetting,
are the Friedmann equations. These equations in HL gravity differ from those of the standard 4D cosmology
inthe presenceofthe parameterλandofthe darkradiationterm. Weexpectthisdeviationfromthestandard
4D cosmologytohavenoticeableeffects onthe cosmologicalphasetransitions. Thefirst-orderphasetransition
have been studied in HL gravity [30], in the context of brane-world scenarios [31] and in a Randall-Sundrum
(RS)brane-worldmodel[32]. Itwouldthereforebeinterestingtostudycrossoverphasetransitionbyusingthe
EoSresultingfromlatticestudies. Inwhatfollows,weshallconcentrateontheoccurrenceofphasetransitionin
the earlyuniverseinthe contextofHL gravity,usingthe type ofphasetransitionandEoSsuggestedbylattice
studies, that is, assuming a smooth crossover quark-hadron phase transition. We also present a comparison
between these results and those when the phase transition is considered to be of first order.
2 Horava-Lifshitz gravity
Horava theory is constructed on the basic assumption of anisotropic scaling between space and time, i.e.
t ℓ3t, xi ℓx. (2)
→ →
In a theory with anisotropic scaling, time and space are fundamentally distinct. It is then natural to use the
ADM formalism for which the metric is given by
ds2 = N2dt2+g dxi+Nidt dxj +Njdt , (3)
ij
−
whereg ,N andN arethespatialmetric,lapsea(cid:0)ndshiftfunc(cid:1)ti(cid:0)ons,respecti(cid:1)vely. Thesevariablesaredynamical
ij i
variables which under the above scaling, scale as
N N, g g , N ℓ2N , Ni ℓ−2Ni. (4)
ij ij i i
→ → → →
2
The action of HL theory is decomposed into a kinetic, a potential and the matter part as
S =S +S +S . (5)
HL k v m
The kinetic action in the Horava-Lifshitz gravity (HL) is naturally given as
2
S = dtdx3N√g K Kij λK2 , (6)
k κ2 ij −
Z
(cid:0) (cid:1)
where K (K =Ki ) is the extrinsic curvature of spatial slices, defined by
ij i
1
K = (∂ g N N ), (7)
ij t ij i j j i
2N −∇ −∇
with being the covariant derivative on the spatial slice whose metric g is used to raise and lower indices.
ij
∇
The most general potential for z =3 can be written as
2
S = − dtd3x√gN[σ+γR+γ R2+γ R Rij +ξεijkR Rl +σ R3+σ RRijR (8)
v κ2 1 2 ij il∇j k 1 2 ij
Z
+ σ RjRkRi +σ R iR+σ R iRjk].
3 i j k 4∇i ∇ 5∇i jk∇
On the other hand, the above ten coefficients can be reduced to three, denoted by µ,Λ ,ζ, using the detailed
W
balance condition [2, 1]
σ = 3κ4µ2Λ2W,γ = κ4µ2ΛW ,γ = κ4µ2(1−4λ),γ = κ4µ2,ξ = κ4µ, (9)
−16(3λ−1) 16(3λ−1) 1 64(3λ−1) 2 16 −4ζ2
σ = κ4 ,σ = 5κ4,σ = 3κ4,σ = 3κ4 ,σ = κ4 ,
1 8ζ4 2 −8ζ4 3 4ζ4 4 −32ζ4 5 4ζ4
where κ2[ 8πG] and Λ are the Einstein coupling and cosmologicalconstants, respectively, and finally
≡ c4 W
S = dtdx3N√gL , (10)
m m
Z
where L = L (N,N ,g ,φ) is the lagrangian density of matter fields, denoted collectively by φ. In the IR
m m i ij
limit the HL action simplifies to
S S dtdx3N√g[α(K Kij λK2)+γR+σ]. (11)
I ij
→ ≃ −
Z
Defining x0 =ct and
γ γ σ
λ=1, c= , 16πG= , Λ = , (12)
α α3 EH −2α
r r
will reduce this action to that of the Einstein-Hilbert
1
S = dx4 g(R 2Λ ) (13)
EH 4 EH
16πG −
Z
1 p
= dtdx3√egeN[KijKij K2+(R 2Λ)].
16πG − −
Z
The full space-time metric g is given by
µν
g = N2+gijN N , g =N ,
e 00 − i j 0i i
g =g , g =N√g. (14)
ij ij
e e
p
There is a condition inferred from the study of some cosmologicalmodels [33], given by
e e
α(3λ 1)>0. (15)
−
3
3 Field equations in Horava-Lifshitz gravity
Now, in order to focus on a cosmologicalframework, we use the FRW metric
N =1, g =a2(t)γ , Ni =0, (16)
ij ij
with
dr2
γ dxidxj = +r2dΩ2. (17)
ij 1 kr2 2
−
The homogeneous and isotropic metric is then written as
dr2
ds2 = dt2+a(t)2 +r2(dθ2+sin2θdφ2) , (18)
− 1 kr2
(cid:20) − (cid:21)
where k = 1, 0, 1 represents an open, flat or closeduniverse, respectively. For the matter energy-momentum
−
tensor we restrict our analysis to the case of a perfect fluid given in comoving coordinates by
T =(ρ+p)u u +pg , u = δt, (19)
µν µ ν µν µ − µ
where ρ, p and u are the energy density, isotropic pressure and four-velocity of the cosmological fluid. We
µ
obtain the gravitationalfield equations of the HL theory, corresponding to the line element (16) and (17) as
κ2 σ kγ 2k2(3γ +γ ) 4k3(9σ +3σ +σ )
3(3λ 1)H2 = ρ+6 + + 1 2 + 1 2 3 , (20)
− 2 6 a2 a4 a6
(cid:20) (cid:21)
3 κ2 σ kγ 2k3(9σ +3σ +σ )
(3λ 1)(H˙ + H2)= p 3 + 1 2 3 , (21)
− 2 − 4 − −6 − 3a2 a6
(cid:20) (cid:21)
with
ρ˙+3H(ρ+p)=0. (22)
Since the earlyuniverseis knowntobe flatto withinagoodapproximation,inthe followweshallfocusonthe
non detailed balance condition with k =0.
4 First order quark-hadron phase transition
In this section, we present a discussion on the derivation of thermodynamical quantities of the quark-hadron
phase transition which corresponds to the first order phase transition. It is now generally accepted that such
phase transition has occurred at the cosmological QCD scale about t 10−5s after the big bang and at a
∼
temperature T 200MeV where the Hubble radius was about 10 km. Note that the mass inside the Hubble
∼
volume is about 1M .
J
In order to study the first order quark-hadron phase transition it is necessary to specify the equation of
state of the matter in both the quark and hadron states. So, at this stage, let us at first discuss the EoS for a
first order phase transition [32] which in the quark phase can generally be given in the form
ρ =3a T4+V(T), p =a T4 V(T), (23)
q q q q
−
where a = (π2/90)g , with g = 16+(21/2)N +14.25 = 51.25 and N = 2. V(T) is a self-interacting
q q q F F
potential, which is expressed as [39]
V(T)=B+γ T2 α T4, (24)
T T
−
whereB isthebagpressureconstantand,accordingtotheresultsobtainedinlowenergyhadronspectroscopy,
heavy ion collisions and phenomenological fits of light hadron properties, the constants are given as B1/4
∈
(100 200)MeV [40], α =7π2/20 and γ =m2/4 with m being the mass of the strange quark in the range
− T T s s
m (60 200)MeV. The shape of the potential V reflects the physical model in which the quark fields are
s
∈ −
interacting with a chiralfield formed out of the π meson and a scalarfield. For the hadronphase, we choose a
4
cosmologicalfluidconsistingofanidealgasofmasslesspionsandnucleonsdescribedbytheMaxwell-Boltzmann
statistics, having an energy density ρ and pressure p , respectively. The equation of state is given by
h h
1
p (t)= ρ (T)=a T4, (25)
h h π
3
wherea =(π2/90)g andg =17.25. Thecriticaltemperature T isdefinedby the conditionp (T )=p (T )
π h h c q c h c
[41], and is given by
γ + γ2 +4(a +α a )B
T = T T q T − π . (26)
c
s p2(aq+αT −aπ)
For m = 200MeV and B1/4 = 200MeV the transition temperature is of the order of T 125MeV. A
s c
≈
first order phase transition incorporates discontinuities for all the physical quantities like the energy density,
pressure and entropy across the critical curve. The quark and hadron energy densities ratio at the critical
temperature, ρ (T )/ρ (T ), is of the order 3.62 for m =200MeV and B1/4 =200MeV.
q c h c s
5 Dynamics of the universe during the first order transition
After determining the equation of state, the physical quantities like the energy density ρ, temperature T,
scale factor a(t) and Habble parameter H can be monitored during the phase transition. These quantities
are determined by the Eqs.(20), (22), (23) and (25). Naturally, there are three stages to distinguish; before
the phase transition where T > T and the universe is likely to be in the quark phase, during the phase
c
transition where T =T and all the quark matter is changed to hadrons and finally, after the phase transition
c
where T < T and the universe is in the hadron phase. Now, using the equations of state of the quark
c
matter, equation(22), the variation of cosmological quantities such as the Hubble parameter, scale factor and
temperature can be written as
a˙ 3a α T˙ 1γ T˙
q T T
H(T)= = − , (27)
a − 3a T − 6 a T3
q q
where after integration we have
a 1 γ 1
a(T)= 0 T(αT−3aq)exp T , (28)
3a 12 a T2
q (cid:18) q (cid:19)
where a is a constant of the integration and the variation of temperature for T >T can be written as
0 c
dT T3 1
= [(3a α )T4+γ T2+B+2σ] (29)
dτ −(1− 3αaTq)T2+ 6γaTq ×s6(3λ−1) q− T T
Figures 1, 2 and 3 show the behavior of temperature as a function of the cosmic time τ , Hubble parameter
and scale factor as a function of temperature in a HL world filled with quark matter for different values of λ
. For T = T , the temperature and pressure are constant. In this case quantities like the entropy S = sa3
c
and enthalpy W =(ρ+p)a3 are conserved. For later convenience, we replace ρ(t) by h(t), so that the volume
fraction of matter in the hadron phase is given by
ρ(t)=ρ (t)+ρ (1 h(t))=ρ (1+mh(t)), (30)
h q Q
−
where m = ρH 1. The beginning of the phase transition is characterized by h(t ) = 0 where t is the time
ρQ − c c
scale and ρ(t ) ρ , while the end of the transition is characterized by h(t ) = 1 with t being the time
c Q h h
≡
signaling the end and corresponding to ρ(t ) ρ . To find the variation of hadron fraction we substitute
h H
≡
equation(30) in the field equations and obtain
dh 3(1+rh(t)) κ2ρ σ 1/2
Q
= (1+mh(t))+ , (31)
dt − r 6(3λ 1) 3(3λ 1)
(cid:20) − − (cid:21)
where r = (ρ ρ )/(ρ + p ). Figure 4 shows variation of the hadron fraction h(τ) as a function of τ
H Q Q c
−
for different values of λ. One may present variation of the Hubble parameter in this case as a function of
the hadron fraction by using the field equation and equation (30), for which the result is shown in figure 5
5
200
180
V160
e
M
ΤL
HT140
120
100
0 2.´10-6 4.´10-6 6.´10-6 8.´10-6 0.00001
ΤMeV-2
Figure 1: Variation of temperature in the T > Tc region as a function of τ = κt in a first order phase transition for different
values of λ:λ=3 (dotted-dashed curve), λ=2 (dotted curve), λ= 1 (solid curve), λ= 0.7 (long dashed curve), and λ= 0.5
(shortdashedcurve),weset κσ2 =106 .
100000
80000
60000
2V
e
M
H 40000
20000
0
0 50 100 150 200
TMeV
Figure 2: VariationoftheHabbleparameter intheT >Tc regionasafunctionoftemperatureinafirstorderphasetransition
fordifferentvaluesofλ:λ=3(dotted-dashedcurve),λ=2(dottedcurve),λ=1(solidcurve),λ=0.7(longdashedcurve),and
λ=0.5(shortdashedcurve),weset κσ2 =106 .
0.0005
0.0004
0.0003
a0
(cid:144)a
0.0002
0.0001
0.0000
130 140 150 160 170 180 190 200
TMeV
Figure 3: Variation of the scale factor in the T > Tc region as a function of temperature in a first order phase transition for
different values of λ:λ=3 (dotted-dashed curve), λ=2 (dotted curve), λ=1 (solid curve), λ=0.7 (long dashed curve), and
λ=0.5(shortdashedcurve),weset κσ2 =106 .
6
1.0
0.8
0.6
ΤL
Hh
0.4
0.2
0.0
0 2.´10-6 4.´10-6 6.´10-6 8.´10-6 0.00001
ΤMeV-2
Figure 4: VariationofthehadronfractionforT =Tc asafunctionofτ =κtinafirstorderphasetransitionfordifferentvalues
of λ: λ= 3 (dotted-dashed curve), λ= 2 (dotted curve), λ= 1 (solid curve), λ=0.7 (long dashed curve), and λ= 0.5 (short
dashedcurve),weset κσ2 =106 .
40000
30000
H20000
10000
0
0.0 0.2 0.4 0.6 0.8 1.0
h
Figure 5: VariationoftheHabbleparameterinT =Tc caseasafunctionofhadronfractioninafirstorderphasetransitionfor
different values of λ:λ=3 (dotted-dashed curve), λ=2 (dotted curve), λ=1 (solid curve), λ=0.7 (long dashed curve), and
λ=0.5(shortdashedcurve),weset κσ2 =106.
7
125
120
V115
e
M
ΤL
HT110
105
100
0 2.´10-6 4.´10-6 6.´10-6 8.´10-6 0.00001
ΤMeV-2
Figure 6: Variation of temperature for T < Tc as a function of τ = κt in a first order phase transition for different values of
λ:λ=3(dotted-dashedcurve),λ=2(dottedcurve),λ=1(solidcurve),λ=0.7(longdashedcurve),andλ=0.5(shortdashed
curve),weset κσ2 =106.
1400
1200
1000
2V 800
e
M
H 600
400
200
0
0 50 100 150 200
TMeV
Figure7: VariationoftheHabbleparameterforT <Tcasafunctionoftemperatureinafirstorderphasetransitionfordifferent
values of λ:λ=3 (dotted-dashed curve), λ=2 (dotted curve), λ= 1 (solid curve), λ= 0.7 (long dashed curve), and λ= 0.5
(shortdashedcurve),weset κσ2 =106.
for different values of λ. For t > t the universe enters into the hadronic phase. For the phase transition
h
temperature of T = 125MeV we have ρ = 5 109MeV4 and ρ = 1.38 109MeV4, respectively. For the
c Q H
× ×
same value of the temperature the value of the pressure of the cosmological fluid during the phase transition
is p = 4.6 108MeV4. Following the same procedure as that in the quark phase, that is, substituting
c
×
equation(25) into (22), the evolution of the scale factor can be obtained where a(τ ) is now determined by
h
using the conservation equation (22) and equations of state for T < T which leads to a(T) = a(τ )T /T. In
c h c
the last stage of the first order phase transition, variation of temperature in the hadron phase (T < T ) for a
c
flat universe leads to
dT κ2a T4 σ
π
= T + . (32)
dt − s2(3λ 1) 3(3λ 1)
− −
The variation of temperature in a first order phase transition as a function of τ =kt and also variation of the
Hubble parameter as a function of temperature are representedfor different values of the coupling constant λ,
infigures 6and7,respectively. Thisparametershowsthatsmallvaluesofthe couplingconstantλreducethe
temperature in these regions. Also, from figures 1 and 6 it is seen that for λ > 1, the temperature is higher
than in generalrelativity (λ=1) whereasfor 1/3<λ<1 the temperature is much lower. In the next section,
we shall consider the evolution of temperature for a crossoverphase transitions in Horava-Lifshitz theory.
6 Crossover quark-hadron phase transition
Indeed, our work is based on results obtained from two different sets of lattice calculations. The hot QCD
collaboration analysis is based on two different improved staggered fermion actions, asqtad and p4, with a
physical strange quark mass and physical u and d quark masses, m /m = 10. It shows that the transition
s u,d
8
region lies in the range T = (185 195)MeV, for recent published results see [37]. Results presented by
−
the other collaborations Points to the value of the transition temperature in the range 150 170MeV, and
−
changes with the observable used to define it [43, 44]. The most recent results for several physical quantities
arepresentedin[42]withthe equationofstateatN =6,8,10and12givenin[45]. We shallrelyonthe above
t
two casesofanalysis to determine the EoSin the contextofthe crossoverphase transitionin this work. In the
first case, the equation of states in both phases are given by the hadron resonance gas (HRG) model at low
temperatures and lattice QCD data at high temperatures, which are combined with a simple parametrization
given in [26]. The equation of state has been calculated with the so-called p4 and asqtad actions on lattices
with temporal extent N =4,6 and 8 [34, 35, 37].
τ
CalculationofthethermodynamicalobservablesinlatticeQCDproceedsthroughthecalculationofthetrace
of the energy momentum tensor Θ(T)=ǫ 3p, also known as the trace anomaly. Different thermodynamical
−
observables can be obtained from the trace anomaly through integration. The pressure can be written as
p(T) p(T ) T dT′
0
= (ρ 3p). (33)
T4 − T4 T′5 −
0 ZT0
Here T is an arbitrary temperature value that is usually chosen in the low-temperature regime where the
0
pressure is exponentially small. This method is known as the integral method [38]. Finite temperature lattice
calculations are mostly performed at a fixed temporal extent N with the temperature being changed by
τ
varying the lattice spacing a, (T =1/N a). Therefore,the lattice spacing becomes smaller as the temperature
τ
isincreased. Asaconsequence,thetraceanomalycanbe calculatedinthe hightemperatureregionaccurately,
whereas at low temperature is affected by the large discretization effects. Thus, to construct a more realistic
equation of state one should use the lattice data for the trace anomaly in the high temperature region, T >
250MeV, and the HRG model otherwise, T <180MeV.
TheHRGmodelwithmodifiedmassesisbelievedtodescribethelatticedataratherwelluptotemperatures
ofabout180MeV. Inthemiddleregion,180MeV <T <250MeV,theHRGmodelcannotbetrusted,whereas
discretization effects in lattice calculations could be large. Therefore, at high temperatures the trace anomaly
can be parameterizedin a polynomial form in general, see e.g. [37]. We shall thus use the following ansatz for
the high temperature region
(ρ 3p) d d c c
2 4 1 2
− = + + + . (34)
T4 T2 T4 Tn1 Tn2
This form is shown to work well in the temperature range of interest and is flexible enough to be matched
to the HRG result in the low temperature region. The resulting parametrization of the trace anomaly and
QCD equation of state obtained using these requirements are labeled as s95p v1, s95n v1 and s90f v1,
− − −
as shown in table 1. The labels “s95” and “s90” refer to the fraction of the ideal entropy density reached at
T =800MeV (95% and 90%, respectively). The labels p, n and f refer to a specific treatment of the peak of
the trace anomaly or its matching to the HRG. Values of the parameters T , d , d , c , c , n and n in are
0 2 4 1 2 1 2
given in table 1. The following form shows a parameterized form for the HRG
(ρ 3p)
− =a T +a T3+a T4+a T10, (35)
T4 1 2 3 4
where a =4.654GeV−1,a = 879GeV−3,a =8081GeV−4 and a = 7039000GeV−10. The importance of
1 2 3 4
− −
the above parametrization and integral method is that we can obtain the thermodynamical quantities for the
low temperature region as
1 1 1
p(T)=(α +β )T4+a T5+ a T7+ a T8+ a T14, (36)
0 0 1 2 3 4
3 4 10
7 13
ρ(T)=3(α +β )T4+4a T5+2a T7+ a T8+ a T14, (37)
0 0 1 2 3 4
4 10
where α and β are the value of integration in the lower limit and the value of p4/T4 when T = 70MeV,
0 0 0 0 0
respectively. For the high temperature region, the pressure and energy density are given by
1 d c c
p(T)= d 2T2+(α +β )T4 1T4−n1 2T4−n2, (38)
4 i i
−4 − 2 − n − n
1 2
1 1 c c
ρ(T)=3(α +β )T4 d T2+ d + 1(n 3)T4−n1 + 2(n 3)T4−n2, (39)
i i 2 4 1 2
− 2 4 n − n −
1 2
9
Table 1: Thevaluesofparametersfordifferentfitstothetraceanomaly[26].
d (GeV) d (GeV4) c (GeVn1) c (GeVn2) n n T (MeV)
2 4 1 2 1 2 0
s95p 0.2660 2.403 10−3 2.809 10−7 6.073 10−23 10 30 183.8
s95n 0.2654 6.563×10−3 −4.370×10−5 5.774× 10−6 8 9 171.8
s90f 0.2495 1.355×10−2 −3.237×10−3 1.439 ×10−14 5 18 170.0
× − × ×
Table 2: Thevalues ofparameters appearing inequation (40)describingthetraceanomalyfornf =2+1andnf =2+1+1
[45].
n h h h f f f g g
f 0 1 2 0 1 2 1 2
2+1 0.1396 0.1800 0.0350 2.76 6.79 5.29 0.47 1.04
− − −
2+1+1 0.1396 0.1800 0.0350 5.59 7.34 5.60 1.42 0.50
− −
where i = 1,2,3 corresponds to different parameterizations which are given in table 1. So, α and β refer to
i i
the values of integration in the lower limit and the value of p /T4 in each case. Equations of state are also
0 0
available in a tabulated form in [36].
As was mentioned above, there is another set of data which we will use for determining the EoS in the
present work for which a simple parametrizationof the trace anomaly, given for n =2+1 flavor and also for
f
an estimate of n = 2+1+1 flavor equation of state, can be found in [45]. We notice that these results are
f
obtained for Symanzik improved gauge and a stout-link improved staggered fermion action on lattices with
temporal extent N =6,8 and 10. The thermodynamicalquantities are presentedas functions of temperature
τ
in the range 100 1000MeV. A global parametrization of the trace anomaly as a function of temperature is
···
given by the following fitted function
ρ 3p
− =exp h /t h /t2 h + f0(tanh(f1t+f2)+1) , (40)
T4 − 1 − 2 × 0 1+g1t+g2t2
(cid:0) (cid:1) h i
where the dimensionless t variableis defined as t=T/(200MeV). The parameterscanbe found in 2able 2. In
this case, the numerical solution is used for determining the EoS. The results of this calculation are presented
in the following section.
7 Dynamical evolution in the crossover phase transition
In this section we shall study the physical quantities of interest, that is, energy density ρ and temperature
T. For the first set of lattice data [37] mentioned before, these quantities are obtained from the Friedmann
equation(20), conservation equation(22) and the equations of state determined by equations(36) and (37)
for low temperature region and equations(38) and (39) for high temperature region in the crossover phase
transition. By assuming a first order phase transition, these quantities can be obtained from the Friedmann
equation(20), conservation equation(22) and equations of state (23) and (25), determined for T > T and
c
T <T , respectively. Using the conservation equation (22) and equation of state which is used for describing
c
the high temperature region, we have
a˙
= (41)
a
12(α +β )T3 d T + c1(n 3)(4 n )T3−n1 + c2(n 3)(4 n )T3−n2
i i − 2 n1 1− − 1 n2 2− − 2 T˙.
− 3(−d2T2+4(αi+βi)T4+ nc11(n1−4)T4−n1+ nc22(n2−4)T4−n2)
Substituting equation(41) in equation(20), the basic equation describing the evolution of temperature of the
universe in the high temperature region can be written as
dT = 3(−d2T2+4(αi+βi)T4+ nc11(n1−4)T4−n1 + nc22(n2−4)T4−n2)
dt −12(αi+βi)T3−d2T + nc11(n1−3)(4−n1)T3−n1 + nc22(n2−3)(4−n2)T3−n2
3(α +β )T4 1d T2+ 1d + c1(n 3)T4−n1 + c2(n 3)T4−n2
κ2 i i − 2 2 4 4 n1 1− n2 2−
× 6(3λ 1)
(cid:20) −
1
σ kA k2B k3C 2
+ + + + , (42)
3(3λ 1) a2 a4(t) a6(t)
− (cid:21)
10