10 research outputs found
Detecting quark matter in the early universe by gravitational waves
For large baryochemical potential, strongly interacting matter might undergo
a first order phase transition at temperatures T ~ 100-200 MeV. Within standard
cosmology, however, the chemical potential is assumed to be very small leading
to a crossover. We discuss implications of a first order QCD transition at high
chemical potential being consistent with current observations. In this
contribution we concentrate on effects on the gravitational wave spectrum.
There are other interesting cosmological signals as a modification of the power
spectrum of dark matter, the production of stellar black holes, and the seeds
for the extragalactic magnetic fields which we briefly address also.Comment: 10 pages, talk given at the symposium "Advances in Nuclear Physics in
Our Time", Goa, India, Nov. 28 - Dec. 2, 201
Cosmological implications of a Dark Matter self-interaction energy density
We investigate cosmological constraints on an energy density contribution of
elastic dark matter self-interactions characterized by the mass of the exchange
particle and coupling constant. Because of the expansion behaviour in a
Robertson-Walker metric we investigate self-interacting dark matter that is
warm in the case of thermal relics. The scaling behaviour of dark matter
self-interaction energy density shows that it can be the dominant contribution
(only) in the very early universe. Thus its impact on primordial
nucleosynthesis is used to restrict the interaction strength, which we find to
be at least as strong as the strong interaction. Furthermore we explore dark
matter decoupling in a self-interaction dominated universe, which is done for
the self-interacting warm dark matter as well as for collisionless cold dark
matter in a two component scenario. We find that strong dark matter
self-interactions do not contradict super-weak inelastic interactions between
self-interacting dark matter and baryonic matter and that the natural scale of
collisionless cold dark matter decoupling exceeds the weak scale and depends
linearly on the particle mass. Finally structure formation analysis reveals a
linear growing solution during self-interaction domination; however, only
non-cosmological scales are enhanced.Comment: 14 pages, 14 figures; version published in Phys. Rev.
A Little Inflation at the Cosmological QCD Phase Transition
In this thesis I explore a new scenario that allows for a strong first order phasetransition of quantum chromodynamics (QCD) at non-negligible baryon density in the early universe and its possible observable consequences. After an introduction to important aspects of the underlying fields of QCD and cosmology I discuss the possibility of a short inflationary phase at the cosmological QCD phase transition. A strong mechanism for baryogenesis is needed to start out with a baryon asymmetry of order unity, e.g. as provided by Affleck-Dine baryogenesis which is also discussed within the thesis. The second main assumption for this ”little inflation” scenario is a quasistable QCD-vacuum state that leads to a short period of exponential expansion consequently diluting the net baryon to photon ratio to today’s observed value. The cosmological implications are among other things direct effects on primordial density fluctuations up to length scales corresponding to an enclosed dark matter mass of 1 M⊙, change in the spectral slope up to 10^6 M⊙, production of strong primordial magnetic fields and a gravitational wave spectrum that could be observed by future pulsar timing gravitational wave detectors
Imprints of the QCD Phase Transition on the Spectrum of Gravitational Waves
We have investigated effects of the QCD phase transition on the relic GW
spectrum applying several equations of state for the strongly interacting
matter: Besides the bag model, which describes a first order transition, we use
recent data from lattice calculations featuring a crossover. Finally, we
include a short period of inflation during the transition which allows for a
first order phase transition at finite baryon density. Our results show that
the QCD transition imprints a step into the spectrum of GWs. Within the first
two scenarios, entropy conservation leads to a step-size determined by the
relativistic degrees of freedom before and after the transition. The inflation
of the third scenario much stronger attenuates the high-frequency modes: An
inflationary model being consistent with observation entails suppression of the
spectral energy density by a factor of ~10^(-12).Comment: 11 pages, 13 figure
Cosmology of fermionic dark matter
We explore a model for a fermionic dark matter particle family which
decouples from the rest of the partices when at least all standard model
particles are in equilibrium. We calculate the allowed ranges for mass and
chemical potential to be compatible with big bang nucleosynthesis (BBN)
calculations and WMAP-data for a flat universe with dark energy. Futhermore we
estimate the free streaming length for fermions and antifermions to allow
comparison to large scale structure data (LLS). We find that for dark matter
decoupling when all standard model particles are present even the least
restrictive combined BBN calculation and WMAP results allow us to constrain the
initial dark matter chemical potential to a highest value of 6.3 times the dark
matter temperature. In this case the resulting mass range is at most 1.8 eV < m
< 53 eV, where the upper bound scales linearly with the effective degrees of
freedom at decoupling. From LSS we find that similar to ordinary warm dark
matter models the particle mass has to be larger than approximately 500 eV
(meaning the effective degrees of freedom at decoupling have to be > 1000) to
be compatible with observations of the Ly alpha forest at high redshift, but
still the dark matter chemical potential over temperature ratio can exceed
unity.Comment: 14 pages, 13 figures; Submitted to Phys. Rev. Lett. D., minor changes
after referee report: references added, several minor extensions (mostly to
the introduction). Also conclusion extended with an additional summary plot
to clarify the result
A little inflation at the cosmological QCD phase transition
We reexamine the recently proposed "little inflation" scenario that allows
for a strong first order phase-transition of QCD at non-negligible baryon
number in the early universe and its possible observable consequences. The
scenario is based on the assumptions of a strong mechanism for baryogenesis and
a quasistable QCD-medium state which triggers a short inflationary period of
inflation diluting the baryon asymmetry to the value observed today. The
cosmological implications are reexamined, namely effects on primordial density
fluctuations up to dark matter mass scales of M_{max} \sim 1 M_{\astrosun},
change in the spectral slope up to M_{max} \sim 10^6 M_{\astrosun},
production of seeds for the present galactic and extragalactic magnetic fields
and a gravitational wave spectrum with a peak frequency around . We discuss the issue of nucleation in more detail and
employ a chiral effective model of QCD to study the impact on small scale
structure formation.Comment: 18 pages, 12 figures, several extensions to the text and structure
formation part was rephrased for better readabilit
The neutron and its role in cosmology and particle physics
Experiments with cold and ultracold neutrons have reached a level of
precision such that problems far beyond the scale of the present Standard Model
of particle physics become accessible to experimental investigation. Due to the
close links between particle physics and cosmology, these studies also permit a
deep look into the very first instances of our universe. First addressed in
this article, both in theory and experiment, is the problem of baryogenesis ...
The question how baryogenesis could have happened is open to experimental
tests, and it turns out that this problem can be curbed by the very stringent
limits on an electric dipole moment of the neutron, a quantity that also has
deep implications for particle physics. Then we discuss the recent spectacular
observation of neutron quantization in the earth's gravitational field and of
resonance transitions between such gravitational energy states. These
measurements, together with new evaluations of neutron scattering data, set new
constraints on deviations from Newton's gravitational law at the picometer
scale. Such deviations are predicted in modern theories with extra-dimensions
that propose unification of the Planck scale with the scale of the Standard
Model ... Another main topic is the weak-interaction parameters in various
fields of physics and astrophysics that must all be derived from measured
neutron decay data. Up to now, about 10 different neutron decay observables
have been measured, much more than needed in the electroweak Standard Model.
This allows various precise tests for new physics beyond the Standard Model,
competing with or surpassing similar tests at high-energy. The review ends with
a discussion of neutron and nuclear data required in the synthesis of the
elements during the "first three minutes" and later on in stellar
nucleosynthesis.Comment: 91 pages, 30 figures, accepted by Reviews of Modern Physic