arXiv subjects

Karsten Jedamzik

Publications and source records attributed to Karsten Jedamzik.

At least 55 records · Page 3Linked to original sources

arXiv2007

Gravitino Dark Matter in the CMSSM With Improved Constraints from BBN

In the framework of the Constrained MSSM we re--examine the gravitino as the lightest superpartner and a candidate for cold dark matter in the Universe. Unlike in other recent studies, we include both a thermal contribution to its relic population from scatterings in the plasma and a non--thermal one from neutralino or stau decays after freeze--out. Relative to a previous analysis [1] we update, extend and considerably improve our treatment of constraints from observed light element abundances on additional energy released during BBN in association with late gravitino production. Assuming the gravitino mass in the GeV to TeV range, and for natural ranges of other supersymmetric parameters, the neutralino region is excluded, while for smaller values of the gravitino mass it becomes allowed again. The gravitino relic abundance is consistent with observational constraints on cold dark matter from BBN and CMB in some well defined domains of the stau region but, in most cases, only due to a dominant contribution of the thermal population. This implies, depending on the gravitino mass, a large enough reheating temperature. If $\mgravitino>1$ GeV then $T_R>10^7$ GeV, if allowed by BBN and other constraints but, for light gravitinos, if $\mgravitino>100$ keV then $T_R>3\times 10^3$ GeV. On the other hand, constraints mostly from BBN imply an upper bound $T_R \lsim {a few}x 10^8\times10^9$ GeV which appears inconsistent with thermal leptogenesis. Finally, most of the preferred stau region corresponds to the physical vacuum being a false vacuum. The scenario can be partially probed at the LHC.

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arXiv2006

Natural gravitino dark matter in SO(10) gauge mediated supersymmetry breaking

It is shown that gravitinos with mass m_{3/2} ~ 0.1-1 MeV may provide suitable cold dark matter candidates in scenarios of gauge mediated supersymmetry breaking (GMSB) under SO(10) grand unification coupled to supergravity, which accommodate a messenger sector of mass scale M_X ~ 10^6 GeV. This is due to the combined effects of renormalizable loop-suppressed operators and generic non-renormalizable ones governing the dilution of a pre-existing equilibrium gravitino abundance via messenger decay. The above range of gravitino and messenger masses can be accommodated in indirect GMSB scenarios. The gravitino abundance does not depend on the post-inflationary reheat temperature and it is shown that leptogenesis can generate successfully the baryon asymmetry.

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arXiv2006

Big Bang Nucleosynthesis Constraints on Hadronically and Electromagnetically Decaying Relic Neutral Particles

Big Bang nucleosynthesis in the presence of decaying relic neutral particles is examined in detail. All non-thermal processes important for the determination of light-element abundance yields of 2H, 3H, 3He, 4He, 6Li, and 7Li are coupled to the thermonuclear fusion reactions to obtain comparatively accurate results. Predicted light-element yields are compared to observationally inferred limits on primordial light-element abundances to infer constraints on the abundances and properties of relic decaying particles with decay times in the interval 0.01 sec < tau < 10^(12) sec. Decaying particles are typically constrained at early times by 4He or 2H, at intermediate times by 6Li, and at large times by the 3He/2H ratio. Constraints are shown for a large number of hadronic branching ratios and decaying particle masses and may be applied to constrain the evolution of the early Universe.

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arXiv2006

Gravitino, Axino, Kaluza-Klein Graviton Warm and Mixed Dark Matter and Reionisation

Stable particle dark matter may well originate during the decay of long-lived relic particles, as recently extensively examined in the cases of the axino, gravitino, and higher-dimensional Kaluza-Klein (KK) graviton. It is shown that in much of the viable parameter space such dark matter emerges naturally warm/hot or mixed. In particular, decay produced gravitinos (KK-gravitons) may only be considered cold for the mass of the decaying particle in the several TeV range, unless the decaying particle and the dark matter particle are almost degenerate. Such dark matter candidates are thus subject to a host of cosmological constraints on warm and mixed dark matter, such as limits from a proper reionisation of the Universe, the Lyman-alpha forest, and the abundance of clusters of galaxies.. It is shown that constraints from an early reionsation epoch, such as indicated by recent observations, may potentially limit such warm/hot components to contribute only a very small fraction to the dark matter.

astro-ph↗

arXiv2006

Gravitino dark matter in gauge mediated supersymmetry breaking

This paper investigates the parameter space of theories with gauge mediated supersymmetry breaking leading to gravitino (cold) dark matter with mass m_{3/2}= 1keV - 10MeV. We pay particular attention to the cosmological role of messenger fields. Cosmology requires that these messengers decay to the visible sector if the lightest messenger mass M_X > 30TeV. We then examine the various possible messenger number violating interactions allowed by the symmetries of the theory and by phenomenology. Late messenger decay generally results in entropy production hence in the dilution of pre-existing gravitinos. We find that in SU(5) grand unification only specific messenger-matter couplings allow to produce the required amount of gravitino dark matter particles. Gravitino dark matter with the correct abundance is however expected in larger gauge groups such as SO(10) for generic non-renormalizable messenger-matter interactions and for arbritrarily high post-inflationary reheating temperatures.

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arXiv2004

Neutralinos, Big Bang Nucleosynthesis and 6Li in Low-Metallicity Stars

The synthesis of Li6 during the epoch of Big Bang nucleosynthesis (BBN) due to residual annihilation of dark matter particles is considered. By comparing the predicted Li6 to observations of this isotope in low-metallicity stars, generic constraints on s-wave dark matter annihilation rates into quarks, gauge bosons, and Higgs bosons are derived. It may be shown that, for example, wino dark matter in anomaly-mediated SUSY breaking scenarios with masses Mx < 250 GeV or light neutralinos with Mx < 20 GeV annihilating into light quarks are, taken face value, ruled out. These constraints may only be circumvented if significant Li6 depletion has occurred in all three low-metallicity stars in which this isotope has been observed to date. In general, scenarios invoking non-thermally generated neutralinos with enhanced annihilation rates for a putative explanation of cosmic ray positron or galactic center as well as diffuse background gamma-ray signals by present-day neutralino annihilation will have to face a stringent Li6 overproduction problem. On the other hand, it is possible that Li6 as observed in low-metallicity stars is entirely due to residual dark matter annihilation during BBN, even for neutralinos undergoing a standard thermal freeze-out.

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arXiv2004

The Evolution of Cosmic Magnetic Fields: From the Very Early Universe, to Recombination, to the Present

(abridged) A detailed examination of the evolution of stochastic magnetic fields between high cosmic temperatures and the present epoch is presented. A simple analytical model matching the results of the 3D MHD simulations allows for the prediction of present day magnetic field correlation lengths and energy. Our conclusions are multi fold. (a) Initial primordial fields with only a small amount of helicity are evolving into maximally helical fields. (b) There exists a correlation between the strength of the magnetic field, B, at the peak of it's spectrum and the location of the peak, given at the present epoch by: B ~ 5x10^{-12} (L/kpc) Gauss, where L is the correlation length determined by the initial magnetic field. (c) Concerning studies of generation of cosmic microwave background (CMBR) anisotropies due to primordial magnetic fields of B~10^{-9} Gauss on ~ 10 Mpc scales, such fields are not only impossible to generate in early causal magnetogenesis scenarios but also seemingly ruled out by distortions of the CMBR spectrum due to magnetic field dissipation on smaller scales and the overproduction of cluster magnetic fields. (d) The most promising detection possibility of CMBR distortions due to primordial magnetic fields may be on much smaller scales at higher multipoles l~10^6 where the signal is predicted to be the strongest. (e) It seems possible that magnetic fields in clusters of galaxies are entirely of primordial origin, without invoking dynamo amplification. Such fields would be of (pre-collapse) strength 10^{-12} - 10^{-11} Gauss with correlation lengths in the kpc range, and would also exist in voids of galaxies.

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arXiv2004

Are Cluster Magnetic Fields Primordial ?

We present results of a detailed and fully non-linear numerical and analytical investigation of magnetic field evolution from the very earliest cosmic epochs to the present. We find that, under reasonable assumptions concerning the efficiency of a putative magnetogenesis era during cosmic phase transitions, surprisingly strong magnetic fields 10^{-13} - 10^{-11} Gauss, on comparatively small scales 100 pc - 10 kpc may survive to the present. Building on prior work on the evolution of magnetic fields during the course of gravitational collapse of a cluster, which indicates that pre-collapse fields of 4\times 10^{-12} Gauss extant on small scales may suffice to produce clusters with acceptable Faraday rotation measures, we question the widely hold view that cluster magnetic fields may not be entirely of primordial origin.

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arXiv2004

Did Something Decay, Evaporate, or Annihilate during Big Bang Nucleosynthesis?

Results of a detailed examination of the cascade nucleosynthesis resulting from the putative hadronic decay, evaporation, or annihilation of a primordial relic during the Big Bang nucleosynthesis (BBN) era are presented. It is found that injection of energetic nucleons around cosmic time 1000 sec may lead to an observationally favored reduction of the primordial Li7/H yield by a factor 2 - 3. Moreover, such sources also generically predict the production of the Li6 isotope with magnitude close to the as yet unexplained high Li6 abundances in low-metallicity stars. The simplest of these models operate at fractional contribution to the baryon density Omega_b h^2> 0.025, slightly larger than that inferred from standard BBN. Though further study is required, such sources, as for example due to the decay of the next-to-lightest supersymmetric particle into GeV gravitinos or the decay of an unstable gravitino in the TeV range of abundance Ω_G h^2\sim 5\times 10^{-4} show promise to explain both the Li6 and Li7 abundances in low metallicity stars.

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arXiv2002

Are there MACHOs in the Milky Way halo?

Microlensing searches aim to detect compact halo dark matter via its gravitational lensing effect on stars within the Large Magellanic Cloud. The most recent results have led to the claim that roughly one fifth of the galactic halo dark matter may be in the form of compact, solar-mass objects. We analyze this hypothesis by considering the goodness-of-fit of the best-fit halo dark matter solutions to the observational data. We show that the distribution of the durations of the observed microlensing events is narrower than that expected to result from a standard halo lens population at 90 to 95% confidence. Only when the fraction of expected background (non-halo) events is significantly increased does the discrepancy between the observed and theoretical event duration distributions disappear. This indicates that it is possible that most of the lenses responsible for the observed microlensing events are not located within the Milky Way halo.

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arXiv2002

Cosmological Deuterium Production in Non-Standard Scenarios

It is widely believed that the cosmic baryon density may be obtained by inferring deuterium abundances in low-metallicity quasar absorption line systems. The implicit assumptions which enter this argument are critically assessed. In particular, the production of deuterium in non-standard Big Bang nucleosynthesis scenarios, the putative production of deuterium in astrophysical environments, and the possible destruction of deuterium via non-standard chemical evolution are discussed.

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arXiv2001

From (p)reheating to nucleosynthesis

This article gives a brief qualitative description of the possible evolution of the early Universe between the end of an inflationary epoch and the end of Big Bang nucleosynthesis. After a general introduction, establishing the minimum requirements cosmologists impose on this cosmic evolutionary phase, namely, successful baryogenesis, the production of cosmic dark matter, and successful light-element nucleosynthesis, a more detailed discussion on some recent developments follows. This latter includes the physics of preheating, the putative production of (alternative) dark matter, and the current status of Big Bang nucleosynthesis.

astro-ph↗

arXiv2000

B-ball Dark Matter and Baryogenesis

It has been recently suggested that stable, supersymmetric B-balls formed in the early universe could not only be the dark matter at the present epoch, but also be responsible for baryogenesis by their partial evaporation at high temperatures. We reinvestigate the efficiency of B-ball baryogenesis and find it to be limited by the diffusion of baryon number away from the B-balls. Successful baryogenesis may only occur for B-balls with charges Q\simle 10^{20} - 5\times 10^{23}, which is close to the observational lower limits on the Q of a significant B-ball dark matter component. We also present some cosmological constraints on the abundances of larger B-balls in the early universe.

hep-ph↗

arXiv2000

Limits on Cosmic Matter--Antimatter Domains from Big Bang Nucleosynthesis

We present detailed numerical calculations of the light element abundances synthesized in a Universe consisting of matter- and antimatter- domains, as predicted to arise in some electroweak baryogenesis scenarios. In our simulations all relevant physical effects, such as baryon-antibaryon annihilations, production of secondary particles during annihilations, baryon diffusion, and hydrodynamic processes are coupled to the nuclear reaction network. We identify two dominant effects, according to the typical spatial dimensions of the domains. Small antimatter domains are dissipated via neutron diffusion prior to He4 synthesis at T_He4 \approx 80 keV, leading to a suppression of the primordial He4 mass fraction. Larger domains are dissipated below T_He4 via a combination of proton diffusion and hydrodynamic expansion. In this case the strongest effects on the elemental abundances are due to anti-p He4 annihilations, leading to an overproduction of He3 relative to H2 and to overproduction of Li6 via non-thermal nuclear reactions. Both effects may result in light element abundances deviating substantially from the standard Big Bang Nucleosynthesis yields and from the observationally inferred values. This allows us to derive stringent constraints on the antimatter parameters. For some combinations of the parameters, one may obtain both, low H2 and low He4, at a common value of the cosmic baryon density, a result seemingly favored by current observational data.

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arXiv1999

On Metric Preheating

We consider the generation of super-horizon metric fluctuations during an epoch of preheating in the presence of a scalar field χquadratically coupled to the inflaton. We find that the requirement of efficient broad resonance is concomitant with a severe damping of super-horizon δχquantum fluctuations during inflation. Employing perturbation theory with backreaction included as spatial averages to second order in the scalar fields and in the metric, we argue that the usual inflationary prediction for metric perturbations on scales relevant for structure formation is not strongly modified.

hep-ph↗

arXiv1998

Big Bang Nucleosynthesis with Matter--Antimatter Domains

We investigate Big Bang nucleosynthesis (hereafter, BBN) in a cosmic environment characterized by a distribution of small-scale matter/antimatter domains. Production of antimatter domains in a baryo-asymmetric universe is predicted in some electroweak baryogenesis scenarios. We find that cosmic antimatter domains of size exceeding the neutron-diffusion length at temperature T approx. 1 MeV significantly affect the light-element production. Annihilation of antimatter preferentially occurs on neutrons such that antimatter domains may yield a reduction of the He-4 abundance relative to a standard BBN scenario. In the limiting case, all neutrons will be removed before the onset of light-element production, and a universe with net baryon number but without production of light elements results. In general, antimatter domains spoil agreement between BBN abundance yields and observationally inferred primordial abundances limits which allows us to derive limits on their presence in the early universe. However, if only small amounts of antimatter are present, BBN with low deuterium and low He-4, as seemingly favored by current observational data, is possible.

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arXiv1998

Non-Standard Big Bang Nucleosynthesis Scenarios

A brief overview of non-standard big bang nucleosynthesis (BBN) scenarios is presented. Trends and results of the light-element nucleosynthesis in BBN scenarios with small-scale or large-scale inhomogeneity, the presence of antimatter domains, stable or unstable massive neutrinos, neutrino oscillations, neutrino degeneracy, or massive decaying particles are summarized.

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arXiv1998

Could MACHOS be Primordial Black Holes formed during the QCD Epoch?

Observations by the MACHO collaboration indicate that a significant fraction of the galactic halo dark matter may be in form of compact objects with masses $M\sim 0.5M_{\odot}$. Identification of these objects as red or white dwarfs is problematic due to stringent observational upper limits on such dwarf populations. Primordial black hole (PBH) formation from pre-existing density fluctuations is facilitated during the cosmic QCD transition due to a significant decrease in pressure forces. For generic initial density perturbation spectra this implies that essentially all PBHs may form with masses close to the QCD-horizon scale, $M_h^{QCD}\sim 1M_{\odot}$. It is possible that such QCD PBHs contribute significantly to the closure density today. I discuss the status of theoretical predictions for the properties of QCD PBH dark matter. Observational signatures of and constraints on a cosmic solar mass PBH population are also discussed.

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