Cosmological axion bounds (2009)
Hannestad, Steen, Hamann, Jan, Mirizzi, Alessandro, Raffelt, Georg G., Wong, Yvonne Y. Y.
We discuss current cosmological constraints on axions, as well as future sensitivities. Bounds on axion hot dark matter are discussed first, and subsequently we discuss both current and future...
The Cosmic Neutrino Background Anisotropy - Linear Theory (2009)
Hannestad, Steen, Brandbyge, Jacob
The cosmic neutrino background anisotropy is calculated for massive neutrino states by solving the full Boltzmann equation. The effect of weak gravitational lensing, including the Limber...
Resolving Cosmic Neutrino Structure: A Hybrid Neutrino N-body Scheme (2009)
Brandbyge, Jacob, Hannestad, Steen
We present the first simulation capable of resolving the structure of neutrino clustering on Mpc scales. The method combines grid- and particle-based methods and achieves very good accuracy on both...
Grid Based Linear Neutrino Perturbations in Cosmological N-body Simulations (2008)
Brandbyge, Jacob, Hannestad, Steen
We present a novel, fast and precise method for including the effect of light neutrinos in cosmological N-body simulations. The effect of the neutrino component is included by using the linear theory...
Hamann, Jan, Hannestad, Steen, Sloth, Martin S., Wong, Yvonne Y. Y.
We revisit the issue of ripples in the primordial power spectra caused by trans-Planckian physics, and the potential for their detection by future cosmological probes. We find that for reasonably...
Neutrino Dark Energy With More Than One Neutrino Species (2008)
Bjaelde, Ole Eggers, Hannestad, Steen
The Mass Varying Neutrino scenario is a model that successfully explains the origin of dark energy while at the same time solves the coincidence problem. The model is, however, heavily constrained by...
Are cosmological neutrinos free-streaming? (2008)
Basboll, Anders, Bjaelde, Ole Eggers, Hannestad, Steen, Raffelt, Georg G.
Precision data from cosmology suggest neutrinos stream freely and hence interact very weakly around the epoch of recombination. We study this issue in a simple framework where neutrinos recouple...
Hamann, Jan, Hannestad, Steen, Melchiorri, Alessandro, Wong, Yvonne Y. Y.
We explore and compare the performances of two nonlinear correction and scale-dependent biasing models for the extraction of cosmological information from galaxy power spectrum data, especially in...
Cosmological constraints on neutrino plus axion hot dark matter: Update after WMAP-5 (2008)
Hannestad, Steen, Mirizzi, Alessandro, Raffelt, Georg G., Wong, Yvonne Y. Y.
We update our previous constraints on two-component hot dark matter (axions and neutrinos), including the recent WMAP 5-year data release. Marginalising over sum m_nu provides m_a < 1.02 eV (95%...
The Effect of Thermal Neutrino Motion on the Non-linear Cosmological Matter Power Spectrum (2008)
Brandbyge, Jacob, Hannestad, Steen, Haugboelle, Troels, Thomsen, Bjarne
We have performed detailed studies of non-linear structure formation in cosmological models with light neutrinos. For the first time the effect of neutrino thermal velocities has been included in a...
The Effect of Thermal Neutrino Motion on the Non-linear Cosmological Matter Power Spectrum (2008)
Brandbyge, Jacob, Hannestad, Steen, Haugbølle, Troels, Thomsen, Bjarne
16 pages, 7 figures.-- Submitted to JCAP.-- PACS numbers: 98.65.Dx, 95.35.+d, 14.60.Pq.
Hamann, Jan, Hannestad, Steen, Sloth, Martin S., Wong, Yvonne Y. Y.
We revisit the issue of ripples in the primordial power spectra caused by trans-Planckian physics, and the potential for their detection by future cosmological probes. We find that for reasonably...
Hamann, Jan, Hannestad, Steen, Melchiorri, Alessandro, Wong, Yvonne Y. Y.
We explore and compare the performances of two nonlinear correction and scale-dependent biasing models for the extraction of cosmological information from galaxy power spectrum data, especially in...
Cosmological constraints on neutrino plus axion hot dark matter: Update after WMAP-5 (2008)
Hannestad, Steen, Mirizzi, Alessandro, Raffelt, Georg G., Wong, Yvonne Y. Y.
We update our previous constraints on two-component hot dark matter (axions and neutrinos), including the recent WMAP 5-year data release. Marginalising over sum m_nu provides m_a < 1.02 eV (95%...
Ultra-high energy Neutrinos from Centaurus A and the Auger hot spot (2007)
Cuoco, Alessandro, Hannestad, Steen
The Pierre Auger collaboration has reported a correlation between Ultra-High Energy Cosmic Rays (UHECR) and nearby Active Galactic Nuclei (AGNs) within 75 Mpc. Two of these events fall within 3...
Aspects of Neutrino Physics in the Early Universe (2007)
Contents Preface v 1 Introduction 1 1.1 Neutrinos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Primordial Nucleosynthesis . . . . . . . . . . . . . . . . . . . . . 2 1.3 Thesis...
Cosmological Mass Limits on Neutrinos, Axions, and (2007)
Other Light Particles, Steen Hannestad, Georg Raffelt
The small-scale power spectrum of the cosmological matter distribution together with other cosmological data provides a sensitive measure of the hot dark matter fraction, leading to restrictive...
Angular Signatures of Annihilating Dark Matter in the Cosmic Gamma-Ray Background (2007)
Cuoco, Alessandro, Brandbyge, Jacob, Hannestad, Steen, Haugboelle, Troels, Miele, Gennaro
The extragalactic cosmic gamma-ray background (CGB) is an interesting channel to look for signatures of dark matter annihilation. In particular, besides the imprint in the energy spectrum, peculiar...
Global neutrino parameter estimation using Markov Chain Monte Carlo (2007)
We present a Markov Chain Monte Carlo global analysis of neutrino parameters using both cosmological and experimental data. Results are presented for the combination of all presently available data...
Cuoco, Alessandro, Hannestad, Steen, Haugboelle, Troels, Kachelriess, Michael, Serpico, Pasquale D.
The arrival directions of ultrahigh energy cosmic rays (UHECRs) may show anisotropies on all scales, from just above the experimental angular resolution up to medium scales and dipole anisotropies....
Unparticle constraints from SN1987A (2007)
Hannestad, Steen, Raffelt, Georg, Wong, Yvonne Y. Y.
The existence of an unparticle sector, weakly coupled to the standard model, would have a profound impact on supernova (SN) physics. Emission of energy into the unparticle sector from the core of...
Cosmological constraints on neutrino plus axion hot dark matter (2007)
Hannestad, Steen, Mirizzi, Alessandro, Raffelt, Georg G., Wong, Yvonne Y. Y.
We use observations of the cosmological large-scale structure to derive limits on two-component hot dark matter consisting of mass-degenerate neutrinos and hadronic axions, both components having...
Neutrino Dark Energy -- Revisiting the Stability Issue (2007)
Bjaelde, Ole Eggers, Brookfield, Anthony W., Van De Bruck, Carsten, Hannestad, Steen, Mota, David F., Schrempp, Lily, ...
A coupling between a light scalar field and neutrinos has been widely discussed as a mechanism for linking (time varying) neutrino masses and the present energy density and equation of state of dark...
Precision measurements of large scale structure with future type Ia supernova surveys (2007)
Hannestad, Steen, Haugboelle, Troels, Thomsen, Bjarne
Type Ia supernovae are currently the best known standard candles at cosmological distances. In addition to providing a powerful probe of dark energy they are an ideal source of information about the...
Observational bounds on the cosmic radiation density (2007)
Hamann, Jan, Hannestad, Steen, Raffelt, Georg G., Wong, Yvonne Y. Y.
We consider the inference of the cosmic radiation density, traditionally parameterised as the effective number of neutrino species N_eff, from precision cosmological data. Paying particular attention...
Neutrino mass from future high redshift galaxy surveys: sensitivity and detection threshold (2007)
Hannestad, Steen, Wong, Yvonne Y. Y.
We calculate the sensitivity of future cosmic microwave background probes and large scale structure measurements from galaxy redshift surveys to the neutrino mass. We find that, for minimal models...
The Matrix Reloaded - on the Dark Energy Seesaw (2007)
Enqvist, Kari, Hannestad, Steen, Sloth, Martin S.
We propose a novel mechanism for dark energy, based on an extended seesaw for scalar fields, which does not require any new physics at energies below the TeV scale. A very light quintessence mass is...
How robust are inflation model and dark matter constraints from cosmological data? (2007)
Hamann, Jan, Hannestad, Steen, Sloth, Martin S., Wong, Yvonne Y. Y.
High-precision data from observation of the cosmic microwave background and the large scale structure of the universe provide very tight constraints on the effective parameters that describe...
Neutrino mass from future high redshift galaxy surveys: sensitivity and detection threshold (2007)
Hannestad, Steen, Wong, Yvonne Y. Y.
We calculate the sensitivity of future cosmic microwave background probes and large scale structure measurements from galaxy redshift surveys to the neutrino mass. We find that, for minimal models...
Cosmological constraints on neutrino plus axion hot dark matter (2007)
Hannestad, Steen, Mirizzi, Alessandro, Raffelt, Georg G., Wong, Yvonne Y. Y.
We use observations of the cosmological large-scale structure to derive limits on two-component hot dark matter consisting of mass-degenerate neutrinos and hadronic axions, both components having...
Observational bounds on the cosmic radiation density (2007)
Hamann, Jan, Hannestad, Steen, Raffelt, Georg G., Wong, Yvonne Y. Y.
We consider the inference of the cosmic radiation density, traditionally parameterised as the effective number of neutrino species N_eff, from precision cosmological data. Paying particular attention...
Unparticle constraints from SN1987A (2007)
Hannestad, Steen, Raffelt, Georg, Wong, Yvonne Y. Y.
The existence of an unparticle sector, weakly coupled to the standard model, would have a profound impact on supernova (SN) physics. Emission of energy into the unparticle sector from the core of...
The Velocity Field of the Local Universe from Measurements of Type Ia Supernovae (2006)
Haugboelle, Troels, Hannestad, Steen, Thomsen, Bjarne, Fynbo, Johan, Sollerman, Jesper, Jha, Saurabh
We present a measurement of the velocity flow of the local universe relative to the CMB rest frame, based on the Jha, Riess & Kirshner (2007) sample of 133 low redshift type Ia supernovae. At a depth...
How robust are inflation model and dark matter constraints from cosmological data? (2006)
Hamann, Jan, Hannestad, Steen, Sloth, Martin S., Wong, Yvonne Y. Y.
High-precision data from observation of the cosmic microwave background and the large scale structure of the universe provide very tight constraints on the effective parameters that describe...
Basboll, Anders, Hannestad, Steen
We have studied the two-body production and decay of a heavy, right-handed neutrino to two light states using the full Boltzmann equation instead of the usual integrated Boltzmann equation which...
Neutrino masses and cosmic radiation density: Combined analysis (2006)
Hannestad, Steen, Raffelt, Georg G.
We determine the range of neutrino masses and cosmic radiation content allowed by the most recent CMB and large-scale structure data. In contrast to other recent works, we vary these parameters...
Probing cosmological parameters with the CMB: Forecasts from full Monte Carlo simulations (2006)
Perotto, Laurence, Lesgourgues, Julien, Hannestad, Steen, Tu, Huitzu, Wong, Yvonne Y. Y.
The Fisher matrix formalism has in recent times become the standard method for predicting the precision with which various cosmological parameters can be extracted from future data. This approach is...
Measuring neutrino masses and dark energy with weak lensing tomography (2006)
Hannestad, Steen, Tu, Huitzu, Wong, Yvonne Y. Y.
Surveys of weak gravitational lensing of distant galaxies will be one of the key cosmological probes in the future. We study the ability of such surveys to constrain neutrino masses and the equation...
Goobar, Ariel, Hannestad, Steen, Mortsell, Edvard, Tu, Huitzu
We have studied bounds on the neutrino mass using new data from the WMAP 3 year data, the Sloan Digital Sky Survey measurement of the baryon acoustic peak, the Type Ia supernovae from SNLS, and the...
The connection between cosmological observations and neutrino physics is discussed in detail. Neutrinos decouple from thermal contact in the early Universe at a temperature of order 1 MeV which...
Measuring neutrino masses and dark energy with weak lensing (2006)
Hannestad, Steen, Tu, Huitzu, Wong, Yvonne Y. Y.
Surveys of weak gravitational lensing of distant galaxies will be one of the key cosmological probes in the future. We study the ability of such surveys to constrain neutrino masses and the equation...
Neutrino masses and cosmic radiation density: Combined analysis (2006)
Hannestad, Steen, Raffelt, Georg G.
We determine the range of neutrino masses and cosmic radiation content allowed by the most recent CMB and large-scale structure data. In contrast to other recent works, we vary these parameters...
Probing cosmological parameters with the CMB: Forecasts from Monte Carlo simulations (2006)
Perotto, Laurence, Lesgourgues, Julien, Hannestad, Steen, Tu, Huitzu, Wong, Yvonne Y. Y.
The Fisher matrix formalism has in recent times become the standard method for predicting the precision with which various cosmological parameters can be extracted from future data. This approach is...
Introduction to neutrino cosmology (2005)
I review the basics of neutrino cosmology, from the question of neutrino decoupling and the presence of sterile neutrinos to the effects of neutrinos on the cosmic microwave background and large...
New constraint on the cosmological background of relativistic particles (2005)
We have derived new bounds on the relativistic energy density in the Universe from cosmic microwave background (CMB), large scale structure (LSS), and type Ia supernova (SNI-a) observations. In terms...
Constraining invisible neutrino decays with the cosmic microwave background (2005)
Hannestad, Steen, Raffelt, Georg
Precision measurements of the acoustic peaks of the cosmic microwave background indicate that neutrinos must be freely streaming at the photon decoupling epoch when T ~ 0.3 eV. This requirement...
Dark energy and dark matter from cosmological observations (2005)
The present status of our knowledge about the dark matter and dark energy is reviewed. Bounds on the content of cold and hot dark matter from cosmological observations are discussed in some detail. I...
Is it possible to tell the difference between fermionic and bosonic hot dark matter? (2005)
Hannestad, Steen, Ringwald, Andreas, Tu, Huitzu, Wong, Yvonne Y. Y.
We study the difference between thermally produced fermionic and bosonic hot dark matter in detail. In the linear regime of structure formation, their distinct free-streaming behaviours can lead to...
Cosmology at present provides the nominally strongest constraint on the masses of standard model neutrinos. However, this constraint extremely dependent on the nature of the dark energy component of...
Supermassive gravitinos, dark matter, leptogenesis and flat direction baryogenesis (2005)
Allahverdi, Rouzbeh, Hannestad, Steen, Jokinen, Asko, Mazumdar, Anupam, Pascoli, Silvia
In general the gravitino mass and/or the soft supersymmetry breaking masses in the observable sector can be much larger than the TeV scale. Depending on the relation between the masses, new important...
Constraints on the sound speed of dark energy (2005)
We have studied constraints on the equation of state, $w$, and speed of sound, c_s, of the dark energy from a joint analysis of data from the cosmic microwave background, large scale structure and...
Constraining invisible neutrino decays with the cosmic microwave background (2005)
Hannestad, Steen, Raffelt, Georg
Precision measurements of the acoustic peaks of the cosmic microwave background indicate that neutrinos must be freely streaming at the photon decoupling epoch when T ~ 0.3 eV. This requirement...
Neutrino mass bounds from cosmology (2004)
Cosmology is at present one of the most powerful probes of neutrino properties. The advent of precision data from the cosmic microwave background and large scale structure has allowed for a very...
We investigate a model where neutrinos are strongly coupled to a new, light scalar field. In this model neutrinos annihilate as soon as they become non-relativistic in the early universe, and a...
Searching for a holographic connection between dark energy and the low-l CMB multipoles (2004)
Enqvist, Kari, Hannestad, Steen, Sloth, Martin S.
We consider the angular power spectrum in a finite universe with different boundary conditions and perform a fit to the CMB, LSS and supernova data. A finite universe could be the consequence of a...
Cosmological bounds on masses of neutrinos and other thermal relics (2004)
With the advent of precision data, cosmology has become an extremely powerful tool for probing particle physics. The prime example of this is the cosmological bound on light neutrino masses. Here I...
Cosmological constraints on the dark energy equation of state and its evolution (2004)
Hannestad, Steen, Mortsell, Edvard
We have calculated constraints on the evolution of the equation of state of the dark energy, w(z), from a joint analysis of data from the cosmic microwave background, large scale structure and...
Probing galaxy density profiles with future supernova surveys (2004)
Mortsell, Edvard, Dahle, Haakon, Hannestad, Steen
In this paper we discuss the possibility to measure the Hubble parameter and the slope of galaxy density profiles using future supernova data. With future supernova surveys such as SNAP, large...
A First Glimpse of String Theory in the Sky? (2004)
Hannestad, Steen, Mersini-Houghton, Laura
We propose a new method for identifying new physics imprints on present observational data in cosmology whereby signatures of string theory are clearly distinguished from imprints of possible...
The current status of neutrino cosmology is reviewed, from the question of neutrino decoupling and the presence of sterile neutrinos to the effects of neutrinos on the cosmic microwave background and...
What is the lowest possible reheating temperature? (2004)
We study models in which the universe exits reheating at temperatures in the MeV regime. By combining light element abundance measurements with cosmic microwave background and large scale structure...
Cosmological mass limits on neutrinos, axions, and other light particles (2004)
Hannestad,Steen, Raffelt,Georg
The small-scale power spectrum of the cosmological matter distribution together with other cosmological data provides a sensitive measure of the hot dark matter fraction, leading to restrictive...
Cosmological mass limits on neutrinos, axions, and other light particles (2004)
Hannestad, Steen, Raffelt, Georg
The small-scale power spectrum of the cosmological matter distribution together with other cosmological data provides a sensitive measure of the hot dark matter fraction, leading to restrictive...
Cosmological mass limits on neutrinos, axions, and other light particles (2003)
Hannestad, Steen, Raffelt, Georg
The small-scale power spectrum of the cosmological matter distribution together with other cosmological data provides a sensitive measure of the hot dark matter fraction, leading to restrictive...
Neutrino cosmology - an update (2003)
Present cosmological observations yield an upper bound on the neutrino mass which is significantly stronger than laboratory bounds. However, the exact value of the cosmological bound is model...
Reconstructing the primordial power spectrum - a new algorithm (2003)
We propose an efficient and model independent method for reconstructing the primordial power spectrum from Cosmic Microwave Background (CMB) and large scale structure observations. The algorithm is...
Cosmology and neutrino masses - an update (2003)
Present cosmological observations yield an upper bound on the neutrino mass which is significantly stronger than laboratory bounds. However, the exact value of the cosmological bound is model...
Neutrino physics from cosmology (2003)
Cosmological observations have in the past few years become an increasingly powerful method for determining parameters within the neutrino sector, such as the presence of sterile states and the mass...
Late-time Entropy Production from Scalar Decay and Relic Neutrino Temperature (2003)
Adhya, Paramita, Chaudhuri, D. Rai, Hannestad, Steen
Entropy production from scalar decay in the era of low temperatures after neutrino decoupling will change the ratio of the relic neutrino temperature to the CMB temperature, and, hence, the value of...
Can Planck-scale physics be seen in the cosmic microwave background ? (2003)
Elgaroy, Oystein, Hannestad, Steen
We investigate the potential of observations of anisotropies in the cosmic microwave background (CMB) and large-scale structure in the Universe to detect possible modifications of standard...
Observational constraints on particle production during inflation (2003)
Elgaroy, Oystein, Hannestad, Steen, Haugboelle, Troels
Resonant particle production, along with many other physical processes which change the effective equation of state (EOS) during inflation, introduces a step-like feature in the primordial power...
Neutrino masses and the number of neutrino species from WMAP and 2dFGRS (2003)
We have performed a thorough analysis of the constraints which can be put on neutrino parameters from cosmological observations, most notably those from the WMAP satellite and the 2dF galaxy survey....
The paper has been withdrawn
Supernova and neutron-star limits on large extra dimensions reexamined (2003)
Hannestad,Steen, Raffelt,Georg
In theories with large extra dimensions, supernova (SN) cores are powerful sources of Kaluza-Klein (KK) gravitons. A large fraction of these massive particles are gravitationally retained by the...
Supernova and neutron-star limits on large extra dimensions reexamined (2003)
Hannestad, Steen, Raffelt, Georg
In theories with large extra dimensions, supernova (SN) cores are powerful sources of Kaluza-Klein (KK) gravitons. A large fraction of these massive particles are gravitationally retained by the...
Can cosmology detect hierarchical neutrino masses? (2002)
We have carefully analysed the potential of future Cosmic Microwave Background (CMB) and Large Scale Structure (LSS) measurements to probe neutrino masses. We perform a Fisher matrix analysis on a...
Neutrino physics from cosmological observations (2002)
We review the current status of neutrino cosmology, focusing mainly on the question of the absolute values of neutrino masses and the possibility of a cosmological neutrino lepton asymmetry.
The Density Profile of Cluster-scale Dark Matter Halos (2002)
Dahle, Haakon, Hannestad, Steen, Sommer-Larsen, Jesper
We measure the average gravitational shear profile of 6 massive clusters (M_vir ~ 10^15 M_sun) at z=0.3 out to a radius ~2h^-1 Mpc. The measurements are fitted to a generalized NFW-like halo model...
Cosmological limit on the neutrino mass (2002)
We have performed a careful analysis of constraints on the neutrino mass from current cosmological data. Combining data from the cosmic microwave background and the 2dF galaxy survey yields an upper...
Hannestad, Steen, Mortsell, Edvard
We have reanalysed constraints on the equation of state parameter, w_Q = P/rho, of the dark energy, using several cosmological data sets and relaxing the usual constraint w_Q > -1. We find that...
A supernova constraint on bulk majorons (2002)
Hannestad, Steen, Keranen, Petteri, Sannino, Francesco
In models with large extra dimensions all gauge singlet fields can in principle propagate in the extra dimensional space. We have investigated possible constraints on majoron models of neutrino...
Chen, Xuelei, Hannestad, Steen, Scherrer, Robert J.
We study the effect on the cosmic microwave background (CMB) anisotropy and large scale structure (LSS) power spectrum of a scattering interaction between cold dark matter and baryons. This...
Stringent neutron-star limits on large extra dimensions (2002)
Hannestad,Steen, Raffelt,Georg G.
Supernovae (SNe) are copious sources for Kaluza-Klein gravitons which are generic for theories with large extra dimensions. These massive particles are produced with average velocities ~0.5 c so that...
Stringent neutron-star limits on large extra dimensions (2002)
Hannestad, Steen, Raffelt, Georg G.
Supernovae (SNe) are copious sources for Kaluza-Klein gravitons which are generic for theories with large extra dimensions. These massive particles are produced with average velocities ~0.5 c so that...
Recent Progress in Neutrino Astrophysics (2001)
Recent progress in neutrino physics has been rapid, to a large extent thanks to observations of neutrinos produced in astrophysical environments. Here, we review the current standing on such...
Oscillation effects on neutrino decoupling in the early universe (2001)
In the early universe, neutrinos decouple from equilibrium with the electromagnetic plasma at a temperature which is only slightly higher than the temperature where electrons and positrons...
Stringent neutron-star limits on large extra dimensions (2001)
Hannestad, Steen, Raffelt, Georg G.
Supernovae (SNe) are copious sources for Kaluza-Klein gravitons which are generic for theories with large extra dimensions. These massive particles are produced with average velocities ~0.5 c so that...
New CMBR data and the cosmic neutrino background (2001)
New precision Cosmic Microwave Background Radiation (CMBR) anisotropy data are beginning to constrain physics beyond the standard model, for example in the form of additional light particle species....
New Supernova Limit on Large Extra Dimensions (2001)
Hannestad, Steen, Raffelt, Georg
If large extra dimensions exist in nature, supernova (SN) cores will emit large fluxes of Kaluza-Klein gravitons, producing a cosmic background of these particles with energies and masses up to about...
Strong constraint on large extra dimensions from cosmology (2001)
We have studied cosmological constraints on the number and radii of possible large extra dimensions. If such dimensions exist, Kaluza-Klein (KK) modes are copiously produced at high temperatures in...
On the chaoticity of active-sterile neutrino oscillations in the early universe (2000)
Braad, Poul-Erik N., Hannestad, Steen
We have investigated the evolution of the neutrino asymmetry in active-sterile neutrino oscillations in the early universe. We find that there are large regions of parameter space where the asymmetry...
Recent CMB Observations and the Ionization History of the Universe (2000)
Hannestad, Steen, Scherrer, Robert J.
Interest in non-standard recombination scenarios has been spurred by recent cosmic microwave background (CMB) results from BOOMERANG and MAXIMA, which show an unexpectedly low second acoustic peak,...
Reconstructing the inflationary power spectrum from CMBR data (2000)
The Cosmic Microwave Background Radiation (CMBR) holds information about almost all the fundamental cosmological parameters, and by performing a likelihood analysis of high precision CMBR fluctuation...
Massive warm dark matter (2000)
Many independent high resolution simulations have indicated that the standard collisionless cold dark matter model does not reproduce the structure of observed present day galaxies well. Several...
On the coupling between different species during recombination (2000)
Measurements of fluctuations in the Cosmic Microwave Background Radiation (CMBR) is one of the most promising methods for measuring the fundamental cosmological parameters. However, in order to infer...
Can dark matter see itself? (2000)
Many independent high-resolution simulations of structure formation in cold dark matter models show that galactic halos should have singular core profiles. This is in stark contrast with observations...
New constraints on neutrino physics from Boomerang data (2000)
We have performed a likelihood analysis of the recent data on the Cosmic Microwave Background Radiation (CMBR) anisotropy taken by the Boomerang experiment. We find that this data places a strong...
Self-interacting Warm Dark Matter (2000)
Hannestad, Steen, Scherrer, Robert J.
It has been shown by many independent studies that the cold dark matter scenario produces singular galactic dark halos, in strong contrast with observations. Possible remedies are that either the...
Updated Bounds on Milli-Charged Particles (2000)
Davidson, Sacha, Hannestad, Steen, Raffelt, Georg
We update the bounds on fermions with electric charge $\epsilon e$ and mass $m_\epsilon$. For $m_\epsilon\lsim m_e$ we find $10^{-15}\lsim\epsilon
Galactic halos of self-interacting dark matter (1999)
Recent, very accurate simulations of galaxy formation have revealed that the standard cold dark matter model has great difficulty in explaining the detailed structure of galaxies. One of the major...
The reconstruction of the CMBR power spectrum from a map represents a major computational challenge to which much effort has been applied. However, once the power spectrum has been recovered there...
Can Dust Segregation Mimic a Cosmological Constant? (1999)
Simonsen, Jakob T., Hannestad, Steen
Recent measurements of type Ia supernovae indicate that distant supernovae are substantially fainter than expected from the standard flat cold dark matter model. One possible explanation is that the...
Combining the baryon budget with CMBR measurements (1999)
Measurements of the Cosmic Microwave Background Radiation (CMBR) provide a powerful tool for measuring the primary cosmological parameters. However, there is a large degree of parameter degeneracy in...
Probing neutrino decays with the cosmic microwave background (1999)
We investigate in detail the possibility of constraining neutrino decays with data from the cosmic microwave background radiation (CMBR). Two generic decays are considered \nu_H -> \nu_L \phi and...
Non-equilibrium effects on particle freeze-out in the early universe (1999)
We investigate the possible effects that deviations from kinetic equilibrium can have on massive particles as they decouple from chemical equilibrium. Different methods of solving the Boltzmann...
The formation of the cosmic microwave background radiation (CMBR) provides a very powerful probe of the early universe at the epoch of recombination. Specifically, it is possible to constrain the...
Post freeze-out annihilations in the early universe (1998)
We investigate the possible effect of the residual annihilations of heavy particles after freeze-out from equilibrium in the early universe. An error in previous work on this subject is pointed out...
Imprint of Sterile Neutrinos in the Cosmic Microwave Background Radiation (1998)
Hannestad, Steen, Raffelt, Georg
The existence of low-mass sterile neutrinos is suggested by the current status of solar and atmospheric neutrinos together with the LSND experiment. In typical four-flavor scenarios, neutrinos would...
Constraining neutrino decays with CMBR data (1998)
The decay of massive neutrinos to final states containing only invisible particles is poorly constrained experimentally. In this letter we describe the constraints that can be put on neutrino mass...
Decay-Produced Neutrino Hot Dark Matter (1998)
We investigate different types of neutrino hot dark matter with respect to structure formation and anisotropies in the cosmic microwave background radiation (CMBR). The possibility of neutrino hot...
Supernova Neutrino Opacity from Nucleon-Nucleon Bremsstrahlung and Related Processes (1997)
Hannestad, Steen, Raffelt, Georg
Elastic scattering on nucleons, \nu N -> N \nu, is the dominant supernova (SN) opacity source for \mu and \tau neutrinos. The dominant energy- and number-changing processes were thought to be \nu e^-...
A Cosmological Three Level Neutrino Laser (1997)
We present a calculation of a neutrino decay scenario in the early Universe. The specific decay is \nu_{2} \to \nu_{1} + \phi, where \phi is a boson. If there is a neutrino mass hierarchy,...
Can Neutrinos be Majorana Particles (1997)
It was recently claimed that the observed physical neutrinos cannot be of Majorana type because such particles lack vector interactions. Contrary to this claim we show that if the Majorana neutrino...
Nucleosynthesis and the mass of the tau neutrino---ERRATUM (1996)
Our results for the primordial abundance of a massive Majorana tau neutrino (hep-ph/9603201) published in PRL76, 2848 (1996) were incorrect due to a trivial (but annoying) error in the numerical...
Nucleosynthesis and the mass of the tau neutrino (1996)
The primordial abundance of long-lived heavy Majorana neutrinos is calculated from the full Boltzmann equation. Inclusion of scattering reactions drastically change the predicted abundance of a heavy...
Neutrino decoupling in the early Universe (1995)
A calculation of neutrino decoupling in the early Universe, including full Fermi-Dirac statistics and electron mass dependence in the weak reaction rates, is presented. We find that after decoupling,...
Are cosmological neutrinos free-streaming?
Basboll, Anders, Bjaelde, Ole Eggers, Hannestad, Steen, Raffelt, Georg G.
Precision data from cosmology suggest neutrinos stream freely and hence interact very weakly around the epoch of recombination. We study this issue in a simple framework where neutrinos recouple...