12 research outputs found
Effective Theories for Hot Non-Abelian Dynamics
The dynamics of soft () non-Abelian gauge fields at
finite temperature is non-perturbative. The effective theory for the soft
fields can be obtained by first integrating out the momentum scale T, which
yields the well known hard thermal loop effective theory. Then the latter is
used to integrate out the scale gT. One obtains a Boltzmann equation, which can
be solved in a leading logarithmic approximation. The resulting effective
theory for the soft fields is described by a Langevin equation, and it is well
suited for non-perturbative lattice simulations.Comment: 11 pages, 3 figures; plenary talk given at Conference on Strong and
Electroweak Matter (SEWM 98), Copenhagen, Denmark, 2-5 Dec 199
Diagrammatic approach to soft non-Abelian dynamics at high temperature
The dynamics of soft () non-Abelian gauge fields at
finite temperature is non-perturbative. The effective theory for the soft scale
is determined by diagrams with external momenta p_0\lsim g^2 T,
and loop momenta larger than . We consider the
polarization tensor beyond the hard thermal loop approximation, which accounts
for loop momenta of order . There are higher loop diagrams, involving also
the scale , which are as important as the hard thermal loops. These higher
loop contributions are characteristic for non-Abelian gauge theories and their
calculation is simplified by using the hard thermal loop effective theory.
Remarkably, the effective one-loop polarization tensor is found to be gauge
fixing independent and transverse at leading order in . The transversality
indicates that this approach leads to a gauge invariant effective theory.Comment: 23 pages, latex, 4 figures, uses axodraw.sty; discussion of higher
loop contributions and of their relation to the Boltzmann equation (Sect. 5)
added, several references added, to appear in Nucl. Phys.
Equilibration of right-handed electrons
We study the equilibration of right-handed electrons in the symmetric phase
of the Standard Model. Due to the smallness of the electron Yukawa coupling, it
happens relatively late in the history of the Universe. We compute the
equilibration rate at leading order in the Standard Model couplings, by
including gauge interactions, the top Yukawa- and the Higgs self-interaction.
The dominant contribution is due to particle scattering, even
though the rate of (inverse) Higgs decays is strongly enhanced by multiple soft
scattering which is included by Landau-Pomeranchuk-Migdal (LPM) resummation.
Our numerical result is substantially larger than approximations presented in
previous literature.Comment: 31 pages, 5 figures. v2: Added appendix estimating the conversion of
right-handed electron number into hypermagnetic fields through the chiral
anomaly. References added, minor errors corrected, results and conclusions
unchanged, published versio
An effective theory for hot non-Abelian dynamics
I try to explain some recent progress in understanding the non-perturbative
dynamics of hot non-Abelian gauge theories. The non-perturbative physics is due
to soft spatial momenta where is the gauge coupling
and is the temperature. An effective theory for the soft field modes is
obtained by integrating out the field modes with momenta of order and of
order in a leading logarithmic approximation. In this effective theory
the time evolution of the soft fields is determined by a local Langevin-type
equation. This effective theory determines the parametric form of the rate for
hot electroweak baryon number violation as . The non-perturbative coefficient is independent of the gauge
coupling and it can be computed by solving the effective equations of motion on
a lattice.Comment: 10 pages, revtex, Talk presented at the 5th International Workshop on
Thermal Field Theories and their Applications, Regensburg, Germany, August
199
QCD plasma instability and thermalisation at heavy ion collisions
Under suitable non-equilibrium conditions QCD plasma can develop plasma
instabilities, where some modes of the plasma grow exponentially. It has been
argued that these instabilities can play a significant role in the
thermalisation of the plasma in heavy-ion collision experiments. We study the
instability in SU(2) plasmas using the hard thermal loop effective lattice
theory, which is suitable for studying real-time evolution of long wavelength
modes in the plasma. We observe that under suitable conditions the plasma can
indeed develop an instability which can grow to a very large magnitude,
necessary for the rapid thermalisation in heavy-ion collisions.Comment: 7 pages, contribution to Lattice 2007, Regensburg, Germany, 30 July -
4 August 200
Can electroweak bubble walls run away?
In extensions of the Standard Model with SU(2) singlet scalar fields, there
can be regions of parameter space for which the electroweak phase transition is
first order already at the mean-field level of analysis. We show that in this
case the phase interface (bubble wall) can become ultra-relativistic, with the
relativistic gamma factor gamma = (1-v_{wall}^2)^{-1/2} growing linearly with
the wall's propagation distance. We provide a simple criterion for determining
whether the bubble wall "runs away" in this way or if gamma approaches a
terminal value.Comment: references adde
The Baryon asymmetry in the Standard Model with a low cut-off
We study the generation of the baryon asymmetry in a variant of the standard
model, where the Higgs field is stabilized by a dimension-six interaction.
Analyzing the one-loop potential, we find a strong first order electroweak
phase transition for Higgs masses up to at least 170 GeV. Dimension-six
operators induce also new sources of CP violation. We compute the baryon
asymmetry in the WKB approximation. Novel source terms in the transport
equations enhance the generated baryon asymmetry. For a wide range of
parameters the model predicts a baryon asymmetry close to the observed value.Comment: 22 pages, latex, 6 figure
Phase Space Description of the Leading Order Quark and Gluon Production from a Space-Time Dependent Chromofield
We derive source terms for the production of quarks and gluons from the QCD
vacuum in the presence of a space-time dependent external chromofield A_{cl} to
the order of S^{(1)}. We found that the source terms for the parton production
processes A_{cl} -> q\bar{q} and A_{cl},A_{cl}A_{cl} -> gg also include the
annihilation processes q\bar{q} -> A_{cl} and gg -> A_{cl},A_{cl}A_{cl}. The
source terms we derive are applicable for the description of the production of
partons with momentum p larger rhan gA which itself must be larger than
\Lambda_{QCD}. We observe that these source terms for the production of partons
from a space-time dependent chromofield can be used to study the production and
equilibration of the quark-gluon plasma during the very early stages of an
ultrarelativistic heavy-ion collision.Comment: 30 pages latex (single spaced), 7 eps figures, Revised Version, To
appear in Physical Review
Baryogenesis from the weak scale to the grand unification scale
We review the current status of baryogenesis with emphasis on electroweak
baryogenesis and leptogenesis. The first detailed studies were carried out for
SU(5) GUT models where CP-violating decays of leptoquarks generate a baryon
asymmetry. These GUT models were excluded by the discovery of B+L violating
sphaleron processes at high temperatures. Yet a new possibility emerged,
electroweak baryogenesis. Here sphaleron processes generate a baryon asymmetry
during a strongly first-order phase transition. This mechanism has been studied
in many extensions of the Standard Model. However, constraints from the LHC and
from low-energy precision experiments exclude most of the known models, leaving
composite Higgs models of electroweak symmetry breaking as an interesting
possibility. Sphaleron processes are also the basis of leptogenesis, where
CP-violating decays of heavy right-handed neutrinos generate a lepton asymmetry
which is partially converted to a baryon asymmetry. This mechanism is closely
related to the one of GUT baryogenesis, and simple estimates based on GUT
models can explain the order of magnitude of the observed baryon-to-photon
ratio. In the one-flavour approximation an upper bound on the light neutrino
masses has been derived which is consistent with the cosmological upper bound
on the sum of neutrino masses. For quasi-degenerate right-handed neutrinos the
leptogenesis temperature can be lowered from the GUT scale down to the weak
scale, and CP-violating oscillations of GeV sterile neutinos can also lead to
successfull leptogenesis. Significant progress has been made in developing a
full field theoretical description of thermal leptogenesis, which demonstrated
that interactions with gauge bosons of the thermal plasma play a crucial role.
Finally, we discuss recent ideas how the seesaw mechanism and B-L breaking at
the GUT scale can be probed by gravitational waves.Comment: 48 pages, 33 figures, 2 tables; a few more correction