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Karsten Jedamzik

Publications and source records attributed to Karsten Jedamzik.

At least 37 records · Page 2Linked to original sources
arXiv2020

Evidence for primordial black hole dark matter from LIGO/Virgo merger rates

The LIGO/Virgo collaboration has by now observed or constrained the gravitational merger rates of different classes of compact objects. We consider the possibility that the bulk of these mergers are primordial black hole (PBH) mergers of PBHs formed during the QCD epoch making up the entirety of the dark matter. Having shown in a companion paper that mergers due to the initial binary population formed in the early Universe are likely negligible, we compute current merger rates in PBH clusters in which the typical PBH resides. We consider two scenarios: (i) the PBH mass function dictated by the QCD equation of state and (ii) the PBH mass function dictated by the existence of a peak in the inflationary perturbation spectrum. In the first scenario, which is essentially parameter free, we reproduce very well the merger rates for heavy BHs, the merger rate of mass-asymmetric BHs such as GW190814, a recently discovered merger of a 23$M_{\odot}$ black hole with a $2.6M_{\odot}$ object, and can naturally explain why LIGO/Virgo has not yet observed mergers of two light PBHs from the dominant $\sim 1\,M_{\odot}$ PBH population. In the second scenario, which has some parameter freedom, we match well the observed rate of heavy PBHs, but can currently not explain the rate for mass-asymmetric events. In either case it is tantalizing that in both scenarios PBH merger rates made with a minimum of assumptions match most LIGO/Virgo observed rates very well.

astro-ph.CO↗
arXiv2019

Stringent Limit on Primordial Magnetic Fields from the Cosmic Microwave Background Radiation

Primordial magnetic fields (PMFs), being present before the epoch of cosmic recombination, induce small-scale baryonic density fluctuations. These inhomogeneities lead to an inhomogeneous recombination process that alters the peaks and heights of the large-scale anisotropies of the cosmic microwave backround (CMB) radiation. Utilizing numerical compressible MHD calculations and a Monte Carlo Markov chain analysis, which compares calculated CMB anisotropies with those observed by the \textit{WMAP} and \textit{Planck} satellites, we derive limits on the magnitude of putative PMFs. We find that the {\it total} remaining present day field, integrated over all scales, cannot exceed 47 pG for scale-invariant PMFs and 8.9 pG for PMFs with a violet Batchelor spectrum at 95\% confidence level. These limits are more than one order of magnitude more stringent than any prior stated limits on PMFs from the CMB which have not accounted for this effect.

astro-ph.CO↗
arXiv2018

Dark matter amnesia in out-of-equilibrium scenarios

Models in which the dark matter is produced at extremely low rates from the annihilation of Standard Model particles in the early Universe allow us to explain the current dark matter relic density while easily evading the traditional experimental constraints. In scenarios where the dark matter interacts with the Standard Model via a new physics mediator, the early Universe dynamics of the dark sector can be particularly complex, as the dark matter and the mediator could be in thermal and chemical equilibrium with each other. This equilibration takes place via number-changing processes such as double Compton scattering and bremsstrahlung, whose amplitudes are cumbersome to calculate. In this paper, we show that in large regions of the parameter space, these equilibration mechanisms do not significantly affect the final dark matter relic density. In particular, for a model with a light dark photon mediator, the relic density can be reasonably estimated by considering that the dark matter is solely produced through the annihilation of Standard Model particles. This result considerably simplifies the treatment of a large class of dark matter theories, facilitating in particular the superimposition of the relic density constraints on the current and future experimental bounds.

hep-ph↗
arXiv2016

Cosmological Constraints on Decoupled Dark Photons and Dark Higgs

Any neutral boson such as a dark photon or dark Higgs that is part of a non-standard sector of particles can mix with its standard model counterpart. When very weakly mixed with the Standard Model, these particles are produced in the early Universe via the freeze-in mechanism and subsequently decay back to standard model particles. In this work, we place constraints on such mediator decays by considering bounds from Big Bang nucleosynthesis and the cosmic microwave background radiation. We find both nucleosynthesis and CMB can constrain dark photons with a kinetic mixing parameter between log ε ~ -10 to -17 for masses between 1 MeV and 100 GeV. Similarly, the dark Higgs mixing angle ε with the Standard Model Higgs is constrained between log ε ~ -6 to -15. Dramatic improvement on the bounds from CMB spectral distortions can be achieved with proposed experiments such as PIXIE.

hep-ph↗
arXiv2013

Evolution of Helical Cosmic Magnetic Fields as Predicted by Magnetohydrodynamic Closure Theory

We extend our recent derivation of the time evolution equations for the energy content of magnetic fields and turbulent motions for incompressible, homogeneous, and isotropic turbulence to include the case of nonvanishing helicity. These equations are subsequently numerically integrated in order to predict the present day primordial magnetic field strength and correlation length, depending on its initial helicity and magnetic energy density. We find that all prior analytic predictions for helical magnetic fields, such as the epoch when they become maximally helical and their subsequent growth of correlation length L ~ a^{1/3} and decrease of magnetic field strength B ~ a^{-1/3} with scale factor a, are well confirmed by the simulations. An initially fully helical primordial magnetic field is a factor 4 10^4 stronger at the present epoch then its nonhelical counterpart when generated during the electroweak epoch.

astro-ph.CO↗
arXiv2013

Gravitino dark matter with constraints from Higgs boson mass and sneutrino decays

We investigate gravitino dark matter produced thermally at high temperatures and in decays of a long-lived sneutrino. We consider the Non-Universal Higgs Model and a generalized gauge mediation model, and in each case identify sneutrino LOSP regions of the parameter space consistent with the mass of the Higgs-like boson observed at the LHC. We apply relevant collider and cosmological bounds, including constraints from Big Bang Nucleosynthesis and from warm dark matter on large scale structures. Generally, we find allowed values of the reheating temperature TR below 10^9 GeV, i.e. somewhat smaller than the values needed for thermal leptogenesis, even with a conservative lower bound of 122 GeV on the Higgs mass. Requiring mass values closer to 126 GeV implies TR below 10^7 GeV and the gravitino mass less than 10 GeV.

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arXiv2012

Time Evolution of the Large-Scale Tail of Nonhelical Primordial Magnetic Fields with Back-Reaction of the Turbulent Medium

We present a derivation of the time evolution equations for the energy content of nonhelical magnetic fields and the accompanying turbulent flows from first principles of incompressible magnetohydrodynamics in the general framework of homogeneous and isotropic turbulence. This is then applied to the early Universe, i.e., the evolution of primordial magnetic fields. Numerically integrating the equations, we find that most of the energy is concentrated at an integral wavenumber scale k_I where the turbulence turn over time equals the Hubble time. At larger length scales L, i.e., smaller wavenumbers q = 2 π/ L << k_I, independent of the assumed turbulent flow power spectrum, mode-mode coupling tends to develop a small q magnetic field tail with a Batchelor spectrum proportional to the fourth inverse power of L and therefore a scaling for the magnetic field of B ~ L^(-5/2).

astro-ph.CO↗
arXiv2011

Weak Primordial Magnetic Fields and Anisotropies in the Cosmic Microwave Background Radiation

It is shown that small-scale magnetic fields present before recombination induce baryonic density inhomogeneities of appreciable magnitude. The presence of such inhomogeneities changes the ionization history of the Universe, which in turn decreases the angular scale of the Doppler peaks and increases Silk damping by photon diffusion. This unique signature could be used to (dis)prove the existence of primordial magnetic fields of strength as small as B~10^(-11) Gauss by upcoming cosmic microwave background observations.

astro-ph.CO↗
arXiv2010

The Evolution of the Large-Scale Tail of Primordial Magnetic Fields

Cosmic magnetic fields may be generated during early cosmic phase transition, such as the QCD- or electroweak- transitions. The magnitude of the remainder of such fields at the present epoch crucially depends on the exponent $n$ of their (initially super-Hubble) large-scale tail, i.e. B(lambda) ~ lambda^(-n). It has been claimed that causality requires n=5/2, contrary to much earlier claims of n=3/2. Here we analyze this question in detail. First, we note that contrary to current belief, the large-scale magnetic field tail is not established at the phase transition itself, but rather continuoulsy evolves up to the present epoch. Neglecting turbulent flows we find n=7/2, i.e. very strongly suppressed large-scale fields. However, in the inevitable presence of turbulent flows we find that the large-scale magnetic field tail has sufficient time to evolve to that of the fluid turbulence. For white noise fluid turbulence this yields n=3/2 up to a certain scale and n=5/2 beyond for the magnetic field spectrum. This picture is also not changed when primordial viscosity and fluid flow dissipation is taken into account. Appreciable primordial magnetic fields originating from cosmic phase transitions seem thus possible.

astro-ph.CO↗
arXiv2010

Generation of gravitational waves during early structure formation between cosmic inflation and reheating

In the pre-reheating era, following cosmic inflation and preceding radiation domination, the energy density may be dominated by an oscillating massive scalar condensate, such as is the case for quadratic chaotic inflation. We have found in a previous paper that during this period, a wide range of sub-Hubble scale perturbations are subject to a preheating instability, leading to the growth of density perturbations ultimately collapsing to form non-linear structures. We compute here the gravitational wave signal due to these structures in the linear limit and present estimates for emission in the non-linear limit due to various effects: the collapse of halos, the tidal interactions, the evaporation during the conversion of the inflaton condensate into radiation and finally the ensuing turbulent cascades. The gravitational wave signal could be rather large and potentially testable by future detectors.

astro-ph.CO↗
arXiv2010

Collapse of Small-Scale Density Perturbations during Preheating in Single Field Inflation

After cosmic inflation and before the transition to radiation domination, the cosmic energy density may have been dominated during an extended period by an oscillating massive scalar condensate. We show that during this period, sub-Hubble scale perturbations are subject to a metric preheating instability in the narrow resonance regime. We analyze in detail both, quadratic and quartic potentials. The instability leads to the growth of density perturbations which in many cases become non-linear already before the beginning of a radiation dominated Universe. This is particularly the case when requiring a phenomenologically preferred low reheat temperature. These early structures may lead to the emission of gravitational waves and the production of primordial black holes. Furthermore, it is not clear if they could modify the prediction of linear curvature perturbations on very large scales.

astro-ph.CO↗
arXiv2009

Freeze-In Production of FIMP Dark Matter

We propose an alternate, calculable mechanism of dark matter genesis, "thermal freeze-in," involving a Feebly Interacting Massive Particle (FIMP) interacting so feebly with the thermal bath that it never attains thermal equilibrium. As with the conventional "thermal freeze-out" production mechanism, the relic abundance reflects a combination of initial thermal distributions together with particle masses and couplings that can be measured in the laboratory or astrophysically. The freeze-in yield is IR dominated by low temperatures near the FIMP mass and is independent of unknown UV physics, such as the reheat temperature after inflation. Moduli and modulinos of string theory compactifications that receive mass from weak-scale supersymmetry breaking provide implementations of the freeze-in mechanism, as do models that employ Dirac neutrino masses or GUT-scale-suppressed interactions. Experimental signals of freeze-in and FIMPs can be spectacular, including the production of new metastable coloured or charged particles at the LHC as well as the alteration of big bang nucleosynthesis.

hep-ph↗
arXiv2009

A Re-analysis of Gravitino Dark Matter in the Constrained MSSM

We re-consider the gravitino as dark matter in the framework of the Constrained MSSM. We include several recently suggested improvements on: (i) the thermal production of gravitinos, (ii) the calculation of the hadronic spectrum from NLSP decay and (iii) the BBN calculation including stau bound-state effects. In most cases we find an upper bound on the reheating temperature $\treh\lsim {\rm a few}\times 10^7\gev$ from over-production of $^6{\rm Li}$ from bound state effects. We also find an upper limit on the stau lifetime of $3\times10^4 \sec$, which is nearly an order of magnitude larger than the simple limit $5\times 10^3 \sec$ often used to avoid the effect of bound-state catalysis. The bound on $\treh$ is relaxed to $\lsim {\rm a few}\times 10^8\gev$ when we use a more conservative bound on ${^6}{\rm Li}/{^7}{\rm Li}$, in which case a new region at small stau mass at $\sim 100\gev$ and much longer lifetimes opens up. Such a low stau mass region can be easily tested at the LHC.

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arXiv2009

Bounds on long-lived charged massive particles from Big Bang nucleosynthesis

The Big Bang nucleosynthesis (BBN) in the presence of charged massive particles (CHAMPs) is studied in detail. All currently known effects due to the existence of bound states between CHAMPs and nuclei, including possible late-time destruction of Li6 and Li7 are included. The study sets conservative bounds on CHAMP abundances in the decay time range 3x10^2 sec - 10^12 sec. It is stressed that the production of Li6 at early times T ~ 10keV is overestimated by a factor ~ 10 when the approximation of the Saha equation for the He4 bound state fraction is utilised. To obtain conservative limits on the abundance of CHAMPs, a Monte-Carlo analysis with ~ 3x10^6 independent BBN runs, varying reaction rates of nineteen different reactions, is performed (see attached erratum, however). The analysis yields the surprising result that except for small areas in the particle parameter space conservative constraints on the abundance of decaying charged particles are currently very close to those of neutral particles. It is shown that, in case a number of heretofore unconsidered reactions may be determined reliably in future, it is conceivable that the limit on CHAMPs in the early Universe could be tightened by orders of magnitude. An ERRATUM gives limits on primordial CHAMP densities when the by Ref. Kamimura et al. recently more accurately determined CHAMP reaction rates are employed.

hep-ph↗
arXiv2009

Gravitino Dark Matter and the Cosmic Lithium Abundances

Supersymmetric extensions of the standard model of particle physics assuming the gravitino to be the lightest supersymmetric particle (LSP), and with the next-to-LSP decaying to the gravitino during Big Bang nucleosynthesis, are analyzed. Particular emphasis is laid on their potential to solve the "Li7 problem", an apparent factor 2-4 overproduction of Li7 in standard Big Bang nucleosynthesis (BBN), their production of cosmologically important amounts of Li6, as well as the resulting gravitino dark matter densities in these models. The study includes several improvements compared to prior studies. Heavy gravitinos in the constrained minimal supersymmetric standard model (CMMSM) are reanalyzed, whereas light gravitinos in gauge-mediated supersymmetry breaking scenarios (GMSB) are studied for the first time. It is confirmed that decays of NLSP staus to heavy gravitinos, while producing all the dark matter, may at the same time resolve the Li7 problem. For NLSP decay times ~ 1000 sec, such scenarios also lead to cosmologically important Li6 (and possibly Be9) abundances. However, as such scenarios require heavy > 1 TeV staus they are likely not testable at the LHC. It is found that decays of NLSP staus to light gravitinos may lead to significant Li6 (and Be9) abundances, whereas NLSP neutralinos decaying into light gravitinos may solve the Li7 problem. Though both scenarios are testable at the LHC they may not lead to the production of the bulk of the dark matter. A section of the paper outlines particle properties required to significantly reduce the Li7 abundance, and/or enhance the Li6 (and possibly Be9) abundances, by the decay of an arbitrary relic particle.

hep-ph↗
arXiv2008

Solving the Cosmic Lithium Problems with Gravitino Dark Matter in the CMSSM

Standard Big Bang nucleosynthesis at baryonic density as inferred by WMAP implies a primordial Li7 abundance factor of two to three larger than that inferred by observations of low--metallicity halo stars. Recent observations of Li6 in halo stars suggest a pre--galactic origin of this isotope, which is exceedingly difficult to explain by putative high redshift cosmic ray populations. We investigate if one or both of these lithium problems may be solved by late decaying relic particles in the Constrained Minimal Supersymmetric Standard Model (CMSSM) coupled to gravity. Assuming that the gravitino is the lightest supersymmetric particle (LSP) we find that in large parts of the CMSSM parameter space either of these problems can be potentially solved. In particular, we also find solutions where both lithium problems may be solved simultaneously. These entail the hadronic decay of relic 1 TeV staus into 100 GeV gravitinos at 1000 sec after the Big Bang, as proposed by one of us before. Moreover, the produced gravitinos naturally contribute a large fraction, or all, to the by WMAP required dark matter density. A prediction of this model is the dark matter to be lukewarm with free--streaming lengths of the order of a 4 keV early freezing--out relic particle. Such lukewarm gravitino dark matter may have beneficial effects to the formation of galactic structures and may be constrained by the reionisation history of the Universe. The current version of the paper presents results for both cases (a) when catalytic nuclear reations are included and (b) when they are neglected.

hep-ph↗
arXiv2007

The cosmic 6Li and 7Li problems and BBN with long-lived charged massive particles

Charged massive particles (CHAMPs), when present during the Big Bang nucleosynthesis (BBN) era, may significantly alter the synthesis of light elements when compared to a standard BBN scenario. This is due to the formation of bound states with nuclei. This paper presents a detailed numerical and analytical analysis of such CHAMP BBN. All reactions important for predicting light-element yields are calculated within the Born approximation. Three priorly neglected effects are treated in detail:(a) photodestruction of bound states due to electromagnetic cascades induced by the CHAMP decay, (b) late-time efficient destruction/production of H2, Li6, and Li7 due to reactions on charge Z=1 nuclei bound to CHAMPs, and (c) CHAMP exchange between nuclei. Each of these effects may induce orders-of-magnitude changes in the final abundance yields. The study focusses on the impact of CHAMPs on a possible simultaneous solution of the Li6 and Li7 problems. It is shown that a priorly suggested simultaneous solution of the Li6 and Li7 problems for a relic decaying at tau_x = 1000 sec is only very weakly dependent on the relic being neutral or charged, unless its hadronic branching ratio is Bh << 10^-4 very small. By use of a Monte-Carlo analysis it is shown that within CHAMP BBN the existence of further parameter space for a simultaneous solution of the Li6 and Li7 problem for long decay times tau_x > 10^6 sec seems possible but fairly unlikely.

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