arXiv subjects

Jes Madsen

Publications and source records attributed to Jes Madsen.

At least 37 records · Page 2Linked to original sources

arXiv2000

Intermediate mass strangelets are positively charged

For a limited range of parameters, stable strange quark matter may be negatively charged in bulk due to one gluon exchange interactions. However, the reduction in strange quark occupation in the surface layer, which is responsible for surface tension, more than compensates this for intermediate mass strangelets, which therefore always have positive quark charge (e.g. for baryon number between 10^2 and 10^{18} assuming alpha_S=0.9). While details are sensitive to the choice of renormalisation, the general conclusion is not. This rules out a scenario where negatively charged strangelets produced in ultrarelativistic heavy ion colliders might grow indefinitely with potentially disastrous consequences.

hep-ph↗

arXiv2000

Probing strange stars and color superconductivity by r-mode instabilities in millisecond pulsars

R-mode instabilities in rapidly rotating quark matter stars (strange stars) lead to specific signatures in the evolution of pulsars with periods below 2.5 msec, and may explain the apparent lack of very rapid pulsars. Existing data seem consistent with pulsars being strange stars with a normal quark matter phase surrounded by an insulating nuclear crust. In contrast, quark stars in a color-flavor-locked (CFL) phase are ruled out. Two-flavor color superconductivity (2SC) is marginally inconsistent with pulsar data.

astro-ph↗

arXiv2000

Does the quark-gluon plasma contain stable hadronic bubbles?

We calculate the thermodynamic potential of bubbles of hadrons embedded in quark-gluon plasma, and of droplets of quark-gluon plasma embedded in hadron phase. This is a generalization of our previous results to the case of non-zero chemical potentials. As in the zero chemical potential case, we find that a quark-gluon plasma in thermodynamic equilibrium may contain stable bubbles of hadrons of radius $R \simeq 1$ fm. The calculations are performed within the MIT Bag model, using an improved multiple reflection expansion. The results are of relevance for neutron star phenomenology and for ultrarelativistic heavy ion collisions.

hep-ph↗

arXiv1999

Free energy of bubbles and droplets in the quark-hadron phase transition

Using the MIT bag model, we calculate the free energy of droplets of quark-gluon plasma in a bulk hadronic medium, and of hadronic bubbles in a bulk quark-gluon plasma, under the assumption of vanishing chemical potentials. We investigate the validity of the multiple reflection expansion approximation, and we advise a novel procedure for calculating finite-size corrections to the free energy of hadronic bubbles in a bulk quark-gluon plasma. While our results agree largely with earlier calculations, we show that the usual multiple reflection expansion should be used with caution, and we propose a modification of the multiple reflection expansion, which makes this approximation agree nicely with direct numerical calculations. The results should be of relevance in connection with the cosmological quark-hadron transition as well as for ultrarelativistic heavy ion collisions.

hep-ph↗

arXiv1998

Physics and Astrophysics of Strange Quark Matter

3-flavor quark matter (strange quark matter; SQM) can be stable or metastable for a wide range of strong interaction parameters. If so, SQM can play an important role in cosmology, neutron stars, cosmic ray physics, and relativistic heavy-ion collisions. As an example of the intimate connections between astrophysics and heavy-ion collision physics, this Chapter gives an overview of the physical properties of SQM in bulk and of small-baryon number strangelets; discusses the possible formation, destruction, and implications of lumps of SQM (quark nuggets) in the early Universe; and describes the structure and signature of strange stars, as well as formation and detection of strangelets in cosmic rays. It is concluded, that astrophysical and laboratory searches are complementary in many respects, and that both should be pursued to test the intriguing possibility of a strange ground state for hadronic matter, and (more generally) to improve our knowledge of the strong interactions.

astro-ph↗

arXiv1998

Detecting supersymmetric Q-balls with neutron stars

Supersymmetric Q-balls trapped in neutron stars or white dwarfs may cause the stars to explode. Trapping of Q-balls in neutron stars is shown to be less likely, but trapping in neutron star progenitors more likely than hitherto assumed, making neutron stars very sensitive Q-ball "detectors". White dwarfs only trap potentially dangerous Q-balls in a narrow parameter range.

hep-ph↗

arXiv1998

How to identify a Strange Star

Contrary to young neutron stars, young strange stars are not subject to the r-mode instability which slows rapidly rotating, hot neutron stars to rotation periods near 10 ms via gravitational wave emission. Young millisecond pulsars are therefore likely to be strange stars rather than neutron stars, or at least to contain significant quantities of quark matter in the interior.

astro-ph↗

arXiv1997

A Cosmological Three Level Neutrino Laser

We present a calculation of a neutrino decay scenario in the early Universe. The specific decay is ν_{2} \to ν_{1} + ϕ, where ϕis a boson. If there is a neutrino mass hierarchy, m_{ν_{e}} < m_{ν_μ} < m_{ν_τ}, we show that it is possible to generate stimulated decay and effects similar to atomic lasing without invoking new neutrinos, even starting from identical neutrino distributions. Under the right circumstances the decay can be to very low momentum boson states thereby producing something similar to a Bose condensate, with possible consequences for structure formation. Finally, we argue that this type of decay may also be important other places in early Universe physics.

astro-ph↗

arXiv1996

Color Singlet Strangelets

When considering strangelets at finite temperature it is important to obey the constraint that any observed state must be color singlet. This constraint results in an increase in strangelet masses as calculated at fixed entropy per baryon. We use the color singlet partition function for an MIT bag, derived using the group theoretical projection method, to calculate strangelet masses. Mean shell effects are included in a liquid drop model, by using a density of states obtained from the multiple reflection expansion. Another important effect of the color singlet restriction, namely many orders of magnitude suppression of thermal nucleation of quark-gluon plasma in collisions, will also briefly be described.

hep-ph↗

arXiv1996

Nucleosynthesis and the mass of the tau neutrino---ERRATUM

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 code. In this ERRATUM we present the corrected results.

hep-ph↗

arXiv1996

Nucleosynthesis and the mass of the tau neutrino

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 species. This loosens the well known mass constraint on MeV neutrinos from Big Bang nucleosynthesis, and allows for the existence of a Majorana tau neutrino with mass m > 11 MeV. Further experimental efforts are therefore needed to investigate the range 11 MeV < m < 24 MeV. Some interesting cosmological consequences of an MeV nu_tau are also pointed out.

hep-ph↗

arXiv1996

Large nucleation distances from impurities in the cosmological quark-hadron transition

We calculate the mean nucleation distance, $d_{nuc}$, in a first order cosmological quark-hadron phase transition. For homogeneous nucleation we find that self-consistent inclusion of curvature energy reduces $d_{nuc}$ to $\lesssim 2$cm. However, impurities can lead to heterogeneous nucleation with $d_{nuc}$ of several meters, a value high enough to change the outcome of Big Bang nucleosynthesis.

astro-ph↗

arXiv1996

Color singlet suppression of quark-gluon plasma formation

The rate of quark-gluon plasma droplet nucleation in superheated hadronic matter is calculated within the MIT bag model. The requirements of color singletness and (to less extent) fixed momentum suppress the nucleation rate by many orders of magnitude, making thermal nucleation of quark-gluon plasma droplets unlikely in ultrarelativistic heavy-ion collisions if the transition is first order and reasonably described by the bag model.

nucl-th↗

arXiv1996

Mixed dark matter with low-mass bosons

We calculate the linear power spectrum for a range of mixed dark matter (MDM) models assuming a massive (few eV) boson, $ϕ$, instead of a neutrino as the hot component. We consider both the case where the hot dark matter (HDM) particle is a boson and the cold component is some other unknown particle, and the case where there is only one dark matter particle, a boson, with the cold dark matter (CDM) component in a Bose condensate. Models resembling the latter type could arise from neutrino decays - we discuss some variants of this idea. The power spectra for MDM models with massive bosons are almost identical to neutrino MDM models for a given mass fraction of HDM if the bosons are distinct from their antiparticles ($ϕ\neq\barϕ$) and have a temperature like that of neutrinos, whereas models with $ϕ=\barϕ$ tend to overproduce small-scale structure.

astro-ph↗

arXiv1996

Is Her X-1 a strange star?

The possible identification of Her X-1 with a strange star (Li et al. 1995) is shown to be incorrect.

astro-ph↗

arXiv1996

Finite Mass Isothermal Spheres and the Structure of Globular Clusters

Utilizing a recently derived extension of the Maxwell-Boltzmann distribution to low occupation numbers (Simons 1994) this investigation discusses the structure of stellar dynamical isothermal spheres. The resulting models, which resemble King models, constitute a new sequence of physically well-motivated spherical equilibrium configurations of finite mass, and give nice fits to pre-core collapse globular cluster data.

astro-ph↗

arXiv1995

Mixed dark matter with neutrino chemical potentials

Mixed dark matter models with one low-mass (e.g. 2.4eV) neutrino flavor are shown to be in good agreement with observations if the neutrinos have non-zero chemical potentials. This agreement holds (except for the problem with a low-age Universe) even for high values of the Hubble-parameter. Massless neutrinos with non-zero chemical potentials may reconcile cold dark matter with observations. Some fine-tuning is required to avoid problems with Big Bang nucleosynthesis.

astro-ph↗

arXiv1995

Neutrino decoupling in the early Universe

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, the electron neutrinos contribute 0.83\% more to the relativistic energy density than in the standard scenario, where neutrinos are assumed not to share the heating from e$^\pm$ annihilation. The corresponding number for muon and tau neutrinos is 0.41\% . This has the consequence of modifying the primordial $^4$He abundance by $ΔY=+1.0\times 10^{-4}$, and the cosmological mass limit on light neutrinos by 0.2--0.5 eV.

astro-ph↗