53 research outputs found
QCD-induced Electroweak Phase Transition
Phase transitions associated with nearly conformal dynamics are known to lead
to significant supercooling. A notorious example is the phase transition in
Randall-Sundrum models or their CFT duals. In fact, it was found that the phase
transition in this case is first-order and the tunneling probability for the
radion/dilaton is so small that the system typically remains trapped in the
false vacuum and the phase transition never completes. The universe then keeps
expanding and cooling. Eventually the temperature drops below the QCD scale. We
show that the QCD condensates which subsequently form give an additional
contribution to the radion/dilaton potential, an effect which had been ignored
so far. This significantly reduces the barrier in the potential and allows the
phase transition to complete in a substantially larger region of parameter
space. Due to the supercooling, electroweak symmetry is then broken
simultaneously. This class of models therefore naturally leads to an
electroweak phase transition taking place at or below QCD temperatures, with
interesting cosmological implications and signatures.Comment: 33 pages, 5 figure
Electroweak Phase Transition and Baryogenesis in Composite Higgs Models
We present a comprehensive study of the electroweak phase transition in
composite Higgs models, where the Higgs arises from a new, strongly-coupled
sector which confines near the TeV scale. This work extends our study in Ref.
[1]. We describe the confinement phase transition in terms of the dilaton, the
pseudo-Nambu-Goldstone boson of broken conformal invariance of the composite
Higgs sector. From the analysis of the joint Higgs-dilaton potential we
conclude that in this scenario the electroweak phase transition can naturally
be first-order, allowing for electroweak baryogenesis. We then extensively
discuss possible options to generate a sufficient amount of CP violation -
another key ingredient of baryogenesis - from quark Yukawa couplings which vary
during the phase transition. For one such an option, with a varying charm quark
Yukawa coupling, we perform a full numerical analysis of tunnelling in the
Higgs-dilaton potential and determine regions of parameter space which allow
for successful baryogenesis. This scenario singles out the light dilaton region
while satisfying all experimental bounds. We discuss future tests. Our results
bring new opportunities and strong motivations for electroweak baryogenesis.Comment: 61 pages, 29 figures, 2 tables; v2: Analysis updated to account for
washout of the baryon asymmetry during reheating after the phase transition,
JHEP versio
Throat Cosmology
In this thesis, we study throats in the early, hot universe. Throats are a common feature of the landscape of type IIB string theory. If a throat is heated during cosmological evolution, energy is subsequently transferred to other throats and to the standard model. We calculate the heat transfer rate and the decay rate of throat-localized Kaluza-Klein states in a ten-dimensional model. For the calculation, we employ the dual description of the throats in terms of gauge theories. We discuss modifications of the decay rate which arise in flux compactifications and for Klebanov-Strassler throats and emphasize the role of tachyonic scalars in such throats in mediating decays of Kaluza-Klein modes. Our results are also applicable to the energy transfer from the heated standard model to throats. We determine the resulting energy density in throats at our epoch in dependence of their infrared scales and of the reheating temperature. The Kaluza-Klein modes in the throats decay to other sectors with a highly suppressed rate. If their lifetime is longer than the age of the universe, they are an interesting dark matter candidate. We show that, if the reheating temperature was 10^10 - 10^11 GeV, throats with infrared scales in the range of 10^5 GeV to 10^10 GeV can account for the observed dark matter. We identify several scenarios where this type of dark matter is sufficiently stable but where decays to the standard model can be discovered via gamma-ray observations
The price of being SM-like in SUSY
We compute the tuning in supersymmetric models associated with the
constraints from collider measurements of the Higgs couplings to fermions and
gauge bosons. In supersymmetric models, a CP-even state with SM Higgs couplings
mixes with additional, heavier CP-even states, causing deviations in the Higgs
couplings from SM values. These deviations are reduced as the heavy states are
decoupled with large soft masses, thereby exacerbating the tuning associated
with the electroweak scale. This new source of tuning is different from that
derived from collider limits on stops, gluinos and Higgsinos. It can be offset
with large tan beta in the MSSM, however this compensating effect is limited in
the NMSSM with a large Higgs-singlet coupling due to restrictions on large tan
beta from electroweak precision tests. We derive a lower bound on this tuning
and show that the level of precision of Higgs coupling measurements at the LHC
will probe naturalness in the NMSSM at the few-percent level. This is
comparable to the tuning derived from superpartner limits in models with a low
messenger scale and split families. Instead the significant improvement in
sensitivity of Higgs coupling measurements at the ILC will allow naturalness in
these models to be constrained at the per-mille level, beyond any tuning
derived from direct superpartner limits.Comment: 29 pages, 6 figure
Anomalous Dimensions of Effective Theories from Partial Waves
On-shell amplitude methods have proven to be extremely efficient for
calculating anomalous dimensions. We further elaborate on these methods to show
that, by the use of an angular momentum decomposition, the one-loop anomalous
dimensions can be reduced to essentially a sum of products of partial waves. We
apply this to the SM EFT, and show how certain classes of anomalous dimensions
have their origin in the same partial-wave coefficients. We also use our result
to obtain a generic formula for the one-loop anomalous dimensions of nonlinear
sigma models at any order in the energy expansion, and apply our method to
gravity, where it proves to be very advantageous even in the presence of IR
divergencies.Comment: 22 pages, 1 figure; v2: signs corrected and conventions clarified,
other minor change
Energy Transfer between Throats from a 10d Perspective
Strongly warped regions, also known as throats, are a common feature of the
type IIB string theory landscape. If one of the throats is heated during
cosmological evolution, the energy is subsequently transferred to other throats
or to massless fields in the unwarped bulk of the Calabi-Yau orientifold. This
energy transfer proceeds either by Hawking radiation from the black hole
horizon in the heated throat or, at later times, by the decay of
throat-localized Kaluza-Klein states. In both cases, we calculate in a 10d
setup the energy transfer rate (respectively decay rate) as a function of the
AdS scales of the throats and of their relative distance. Compared to existing
results based on 5d models, we find a significant suppression of the energy
transfer rates if the size of the embedding Calabi-Yau orientifold is much
larger than the AdS radii of the throats. This effect can be partially
compensated by a small distance between the throats. These results are
relevant, e.g., for the analysis of reheating after brane inflation. Our
calculation employs the dual gauge theory picture in which each throat is
described by a strongly coupled 4d gauge theory, the degrees of freedom of
which are localized at a certain position in the compact space.Comment: 25 pages; a comment adde
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