Thermodynamic equilibrium with acceleration and the Unruh...
Transcript of Thermodynamic equilibrium with acceleration and the Unruh...
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Thermodynamic equilibrium with acceleration and the Unruh effect
F. B., arXiv:1712.08031 to appear in Phys. Rev. D
OUTLINE
General global thermodynamic equilibria in flat spacetimeThermodynamic equilibrium with acceleration(Scalar) Quantum field theory in Rindler coordinatesThermal expectation values and vacuum subtraction
PAFT 2018, Vietri sul Mare (SA) March 27 2018
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Motivations
Quantum field theory in nontrivial and local thermal equilibrium
Description of fluids in local equilibrium with large accelerations (QGP in heavy ion collisions has initial acceleration a ~ 1030 g)
Stressenergy tensor in general relativity beyond ideal fluid approximation including quantum effects
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In a quantum statistical framework, the stressenergy tensor is defined as:
The density operator of the familiar global thermodynamical equilibrium in flat spacetime (in covariant form):
energy density
Mean values
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General covariant (local) equilibriumZubarev 1979 Weert 1982
This operator is obtained by maximizing the entropy with the constraints of energy densityand momentum density
F. B., L. Bucciantini, E. Grossi, L. Tinti, Eur. Phys. J. C 75 (2015) 191( frame)
T. Hayata, Y. Hidaka, T. Noumi, M. Hongo, Phys. Rev. D 92 (2015) 065008
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Solution of the Killing equation in Minkowski spacetime:
constant
Thermal vorticityAdimensional in natural units
General covariant global t.d. equilibrium in flat spacetime
If the divergence of the integrand vanishes, that is:
can now be an arbitrary general timelike 3D hypersurface
For global equilibrium (=1/T u) must be a Killing vector
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General global equilibrium 2
with
Plugging the solution into the general covariant expression of the density operator:
Therefore, the most general thermodynamical equilibrium in Minkowski spacetime involvesthe 10 generators of its maximal symmetry group.
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Special casesPure rotation (Landau Statistical Physics)
Pure acceleration (the subject of this talk)
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What is it?
Single nonrelativistic particle (restoring c)
Hamiltonian of a particle in a constant and uniform gravitational field
H and K are both constant (even if they do not commute)
At t=0
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Flow features
Shift the origin: z' = z 1/a
Field lines are hyperbolae with constant
Velocity field
Comoving acceleration A2 constantalong flow lines (relativistic uniformlyaccelerated motion)
T0, a constants
Acceleration field
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Space time diagram
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Thermal features
Comoving temperature – constantalong flow lines (implied by Killingequation)
T0, a constants
Ratio between comoving acceleration and comoving temperature is constant
Temperature measured by a thermometer at rest with the inertial observer = 1/0
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Rewriting the density operator(no chemical potential for simplicity)
Because the Killing vector or vanishes in z’=0
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Decoupling of RRW and LRW
Factorization of the density operator in the RRW and LRW
With operators acting on the Hilbert spaces of the field degrees of freedom in the RRW and LRW
Partition function also factorizes:
The mean value of a local operator only involves the wedge x belongs to. If x RRW:
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Quantum field theory in Rindler coordinates
1 KleinGordon inner product
is the (arbitrary) spacelike quantization hypersurface
2 – Expand the field into (normalized) eigenfunctions of the KG equation, with positive and negative frequencies of the normal derivative at the hypersurface
L.C.B. Crispino, A. Higuchi and G.E.A. Matsas, The Unruh effect and its applications, Rev. Mod. Phys. 80 (2008) 787
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3 – Enforce quantization
Note that:
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Quantum field theory in Rindler coordinates (cont'd)
To calculate mean values with exp (/T0), it is convenient to quantize in Rindler coordinates.
This requires the introduction of two different coordinates set for the RRW and the LRW
RRW
LRW
is the generator of translations along the Killing field lines
It can be shown that
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The eigenfunctions are the same in both wedges, but the role of creation and destruction operators is interchanged because the positive time direction is opposite to in the LRW
General eigenfunction
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Space time diagram
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Thermalacceleration field theoryObjective: calculate mean values of local operators with density operator
1 Define inner operator product
2 Show that
3 – Calculate :
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This form of the P operator makes it easy to determine the thermal expectation values(TEV) of quadratic combinations of Rindler creation and annihilation operators by using the Familiar method in thermal field theory:
Thermal expectation values of particle number operators
In the RRW
whereas in the LRW
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Any quadratic operator in the fields in the RRW will have a T.E.V.where A and B are operations such as multiplication for a scalar or derivation.
This term gives rise to an infinite and must be renormalized
Renormalizing T.E.V.s
The usual renormalization in freefield theory is carried out by subtracting the Minkowski vacuum contribution. It seems reasonable to do the same here
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Renormalizing T.E.V.s and Unruh effect
These (Minkowski) V.E.V.s are the well known content of the Unruh effect:
Therefore, the renormalization results in:
Which means that the renormalized T.E.V. of any quadratic quantity vanishes when T0 = a/2
This conclusion extends to interacting field theories because (Bisognano Wichmann 1975)
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ConsequenceAll quadratic operators (including the stressenergy tensor) have a vanishing mean value when T
0 = 2/a and not when T
0 = 0
Note that so when T0 = 2/a
Comoving thermometer sees comoving Unruh temperature
An ideal thermometer moving along the accelerated world lines in the Minkowskivacuum state always marks a proper temperature equal to the magnitude of its proper acceleration divided by 2. This must be an absolute lower bound.
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Lorentz invariance and an exampleThe T.E.V. of a Lorentz scalar can only depend on the proper T and A
For the energy density one obtains an exact value:
for the canonical stressenergy tensor, there is a quantumrelativistic correction quadratic inthe acceleration.The exact value corresponds to the first term of the expansion in A2 obtained inF.B., E. Grossi, Phys. Rev. D 92, 045037 (2015)
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Conclusions
● Study of thermal equilibrium in QFT with acceleration
● The comoving observer – according to the Unruh effect – in the Minkowskivacuum – sees a thermal radiation. Thus, it is reasonable that, there is anabsolute lower bound, for an accelerated fluid: T < T
U
● This conclusion applies to the global equilibrium and likely related to the Killinghorizon, difficult to extend it to a general local thermodynamic equilibrium
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For an interacting scalar field theory:
Bisognano Wichmann 1975