78 research outputs found
Skyrmion Multi-Walls
Skyrmion walls are topologically-nontrivial solutions of the Skyrme system
which are periodic in two spatial directions. We report numerical
investigations which show that solutions representing parallel multi-walls
exist. The most stable configuration is that of the square -wall, which in
the limit becomes the cubically-symmetric Skyrme crystal. There is
also a solution resembling parallel hexagonal walls, but this is less stable.Comment: 7 pages, 1 figur
Leptogenesis as the origin of matter
We explore in some detail the hypothesis that the generation of a primordial
lepton-antilepton asymmetry (Leptogenesis) early on in the history of the
Universe is the root cause for the origin of matter. After explaining the
theoretical conditions for producing a matter-antimatter asymmetry in the
Universe we detail how, through sphaleron processes, it is possible to
transmute a lepton asymmetry -- or, more precisely, a (B-L)-asymmetry -- into a
baryon asymmetry. Because Leptogenesis depends in detail on properties of the
neutrino spectrum, we review briefly existing experimental information on
neutrinos as well as the seesaw mechanism, which offers a theoretical
understanding of why neutrinos are so light. The bulk of the review is devoted
to a discussion of thermal Leptogenesis and we show that for the neutrino
spectrum suggested by oscillation experiments one obtains the observed value
for the baryon to photon density ratio in the Universe, independently of any
initial boundary conditions. In the latter part of the review we consider how
well Leptogenesis fits with particle physics models of dark matter. Although
axionic dark matter and Leptogenesis can be very naturally linked, there is a
potential clash between Leptogenesis and models of supersymmetric dark matter
because the high temperature needed for Leptogenesis leads to an overproduction
of gravitinos, which alter the standard predictions of Big Bang
Nucleosynthesis. This problem can be resolved, but it constrains the
supersymmetric spectrum at low energies and the nature of the lightest
supersymmetric particle (LSP). Finally, as an illustration of possible other
options for the origin of matter, we discuss the possibility that Leptogenesis
may occur as a result of non-thermal processes.Comment: 53 pages, minor corrections, one figure and references added, matches
published versio
Sphalerons and the Electroweak Phase Transition in Models with Higher Scalar Representations
In this work we investigate the sphaleron solution in a
gauge theory, which also encompasses the Standard Model, with higher scalar
representation(s) (). We show that the field profiles
describing the sphaleron in higher scalar multiplet, have similar trends like
the doublet case with respect to the radial distance. We compute the sphaleron
energy and find that it scales linearly with the vacuum expectation value of
the scalar field and its slope depends on the representation. We also
investigate the effect of gauge field and find that it is small for the
physical value of the mixing angle, and resembles the case for the
doublet. For higher representations, we show that the criterion for strong
first order phase transition, , is relaxed with respect to
the doublet case, i.e. .Comment: 20 pages, 5 figures & 1 table, published versio
Planck Scale Boundary Conditions and the Higgs Mass
If the LHC does only find a Higgs boson in the low mass region and no other
new physics, then one should reconsider scenarios where the Standard Model with
three right-handed neutrinos is valid up to Planck scale. We assume in this
spirit that the Standard Model couplings are remnants of quantum gravity which
implies certain generic boundary conditions for the Higgs quartic coupling at
Planck scale. This leads to Higgs mass predictions at the electroweak scale via
renormalization group equations. We find that several physically well motivated
conditions yield a range of Higgs masses from 127-142 GeV. We also argue that a
random quartic Higgs coupling at the Planck scale favors M_H > 150 GeV, which
is clearly excluded. We discuss also the prospects for differentiating
different boundary conditions imposed for \lambda(M_{pl}) at the LHC. A
striking example is M_H = 127\pm 5 GeV corresponding to \lambda(M_{pl})=0,
which would imply that the quartic Higgs coupling at the electroweak scale is
entirely radiatively generated.Comment: 12 pages, 5 figures; references added and other minor improvements,
matches version published in JHE
Three-loop \beta-functions for top-Yukawa and the Higgs self-interaction in the Standard Model
We analytically compute the dominant contributions to the \beta-functions for
the top-Yukawa coupling, the strong coupling and the Higgs self-coupling as
well as the anomalous dimensions of the scalar, gluon and quark fields in the
unbroken phase of the Standard Model at three-loop level. These are mainly the
QCD and top-Yukawa corrections. The contributions from the Higgs
self-interaction which are negligible for the running of the top-Yukawa and the
strong coupling but important for the running of the Higgs self-coupling are
also evaluated.Comment: 22 pages, 7 figures. Few extra citations are added; the plots are
improved. Results in computer readable form can be retrieved from
http://www-ttp.particle.uni-karlsruhe.de/Progdata/ttp12/ttp12-012
Phase transitions in the early and the present Universe
The evolution of the Universe is the ultimate laboratory to study fundamental
physics across energy scales that span about 25 orders of magnitude: from the
grand unification scale through particle and nuclear physics scales down to the
scale of atomic physics. The standard models of cosmology and particle physics
provide the basic understanding of the early and present Universe and predict a
series of phase transitions that occurred in succession during the expansion
and cooling history of the Universe. We survey these phase transitions,
highlighting the equilibrium and non-equilibrium effects as well as their
observational and cosmological consequences. We discuss the current theoretical
and experimental programs to study phase transitions in QCD and nuclear matter
in accelerators along with the new results on novel states of matter as well as
on multi- fragmentation in nuclear matter. A critical assessment of
similarities and differences between the conditions in the early universe and
those in ultra- relativistic heavy ion collisions is presented. Cosmological
observations and accelerator experiments are converging towards an
unprecedented understanding of the early and present Universe.Comment: 41 pages, 16 figures, to appear in Ann. Rev. Nucl. Part. Sci 2006.
Presentation improved, references adde
Electroweak baryogenesis and low energy supersymmetry
Electroweak baryogenesis is an interesting theoretical scenario, which
demands physics beyond the Standard Model at energy scales of the order of the
weak boson masses. It has been recently emphasized that, in the presence of
light stops, the electroweak phase transition can be strongly first order,
opening the window for electroweak baryogenesis in the MSSM. For the
realization of this scenario, the Higgs boson must be light, at the reach of
the LEP2 collider. In this article, we compute the baryon asymmetry assuming
the presence of non-trivial CP violating phases in the parameters associated
with the left-right stop mixing term and the Higgsino mass . We conclude
that a phase and Higgsino and gaugino mass
parameters , and of the order of the electroweak scale, are
necessary in order to generate the observed baryon asymmetry.Comment: 20 pages, latex + psfig, 3 figure
Baryon Washout, Electroweak Phase Transition, and Perturbation Theory
We analyze the conventional perturbative treatment of sphaleron-induced
baryon number washout relevant for electroweak baryogenesis and show that it is
not gauge-independent due to the failure of consistently implementing the
Nielsen identities order-by-order in perturbation theory. We provide a
gauge-independent criterion for baryon number preservation in place of the
conventional (gauge-dependent) criterion needed for successful electroweak
baryogenesis. We also review the arguments leading to the preservation
criterion and analyze several sources of theoretical uncertainties in obtaining
a numerical bound. In various beyond the standard model scenarios, a realistic
perturbative treatment will likely require knowledge of the complete two-loop
finite temperature effective potential and the one-loop sphaleron rate.Comment: 25 pages, 9 figures; v2 minor typos correcte
Photometric redshifts for supernovae Ia in the Supernova Legacy Survey
We present a method using the SALT2 light curve fitter to determine the
redshift of Type Ia supernovae in the Supernova Legacy Survey (SNLS) based on
their photometry in g', r', i' and z'. On 289 supernovae of the first three
years of SNLS data, we obtain a precision on
average up to a redshift of 1.0, with a higher precision of 0.016 for z<0.45
and a lower one of 0.025 for z>0.45. The rate of events with (catastrophic errors) is 1.4%. Both the precision and the rate
of catastrophic errors are better than what can be currently obtained using
host galaxy photometric redshifts. Photometric redshifts of this precision may
be useful for future experiments which aim to discover up to millions of
supernovae Ia but without spectroscopy for most of them.Comment: 7 pages, 9 figures, published in Astronomy and Astrophysic
Real-time fermions for baryogenesis simulations
We study how to numerically simulate quantum fermions out of thermal equilibrium, in the context of electroweak baryogenesis. We find that by combining the lattice implementation of Aarts and Smit [1] with the "low cost" fermions of Borsanyi and Hindmarsh [2], we are able to describe the dynamics of a classical bosonic system coupled to quantum fermions, that correctly reproduces anomalous baryon number violation. To demonstrate the method, we apply it to the 1+1 dimensional axial U(1) model, and perform simulations of a fast symmetry breaking transition. Compared to solving all the quantum mode equations as in [1], we find that this statistical approach may lead to a significant gain in computational time, when applied to 3+1 dimensional physics
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