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Search Results: 1 - 10 of 118005 matches for " T. Enqvist "
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Scale-dependence of Non-Gaussianity in the Curvaton Model
Christian T. Byrnes,Kari Enqvist,Tomo Takahashi
Physics , 2010, DOI: 10.1088/1475-7516/2010/09/026
Abstract: We investigate the scale-dependence of f_NL in the self-interacting curvaton model. We show that the scale-dependence, encoded in the spectral index n_{f_NL}, can be observable by future cosmic microwave background observations, such as CMBpol, in a significant part of the parameter space of the model. We point out that together with information about the trispectrum g_NL, the self-interacting curvaton model parameters could be completely fixed by observations. We also discuss the scale-dependence of g_NL and its implications for the curvaton model, arguing that it could provide a complementary probe in cases where the theoretical value of n_{f_NL} is below observational sensitivity.
Production of Neutron-rich Heavy Residues and the Freeze-out Temperature in the Fragmentation of Relativistic 238U Projectiles Determined by the Isospin Thermometer
K. -H. Schmidt,M. V. Ricciardi,A. Botvina,T. Enqvist
Physics , 2002, DOI: 10.1016/S0375-9474(02)01120-X
Abstract: Isotope yields of heavy residues produced in collisions of 238U with lead at 1AGeV show indications for a simultaneous break-up process. From the average N-over-Z ratio of the final residues up to Z = 70, the average limiting temperature of the break-up configuration at freeze out was determined to T approximately 5 MeV using the isospin-thermometer method. Consequences for the understanding of other phenomena in highly excited nuclear systems are discussed.
Strongly scale-dependent polyspectra from curvaton self-interactions
Christian T. Byrnes,Kari Enqvist,Sami Nurmi,Tomo Takahashi
Physics , 2011, DOI: 10.1088/1475-7516/2011/11/011
Abstract: We study the scale dependence of the non-linearity parameters f_NL and g_NL in curvaton models with self-interactions. We show that the spectral indices n_fNL=d ln|f_NL|/(d ln k) and n_gNL=d ln |g_NL|/(d ln k) can take values much greater than the slow--roll parameters and the spectral index of the power spectrum. This means that the scale--dependence of the bi and trispectrum could be easily observable in this scenario with Planck, which would lead to tight additional constraints on the model. Inspite of the highly non-trivial behaviour of f_NL and g_NL in the curvaton models with self-interactions, we find that the model can be falsified if g_NL(k) is also observed.
Numerical simulations of fragmentation of the Affleck-Dine condensate
K. Enqvist,A. Jokinen,T. Multamaki,I. Vilja
Physics , 2000, DOI: 10.1103/PhysRevD.63.083501
Abstract: We present numerical simulations of fragmentation of the Affleck-Dine condensate in two spatial dimensions. We argue analytically that the final state should consist of both Q-balls and anti-Q-balls in a state of maximum entropy, with most of the balls small and relativistic. Such a behaviour is found in simulations on a 100x100 lattice with cosmologically realistic parameter values. During fragmentation process, we observe filament-like texture in the spatial distribution of charge. The total charge in Q-balls is found to be almost equal to the charge in anti-Q-balls and typically orders of magnitude larger than charge asymmetry. Analytical considerations indicate that, apart from geometrical factors, the results of the simulated two dimensional case should apply also to the fully realistic three dimensional case.
Constraints on self-interacting Q-ball dark matter
K. Enqvist,A. Jokinen,T. Multamaki,I. Vilja
Physics , 2001, DOI: 10.1016/S0370-2693(01)01500-3
Abstract: We consider different types of Q-balls as self-interacting dark matter. For the Q-balls to act as the dark matter of the universe they should not evaporate, which requires them to carry very large charges; depending on the type, the minimum charge could be as high as Q \sim 10^{33} or the Q-ball coupling to ordinary matter as small as \sim 10^{-35}. The cross-section-to-mass ratio needed for self-interacting dark matter implies a mass scale of m \sim O(1) MeV for the quanta that the Q-balls consist of, which is very difficult to achieve in the MSSM.
Q-balls in the MSSM
Kari Enqvist
Physics , 1998,
Abstract: In the MSSM with gravity mediated supersymmetry breaking, there may exist unstable but long-lived solitons carrying large baryonic charge, or B-balls. These decay well afterthe electroweak phase transition, giving rise to B-ball baryogenesis. Being made of squarks, B-ball decays produce also LSPs and hence can be the source for all cold dark matter.
On Primordial Magnetic Fields
Kari Enqvist
Physics , 1994,
Abstract: A primordial magnetic field could be responsible for the observed magnetic fields of the galaxies. One possibility is that such a primordial field is generated at the electroweak phase transition because of the fluctuations in the Higgs field gradients. I describe a statistical averaging procedure which gives rise to a field of a correct magnitude. Another possibility, where the Yang-Mills vacuum itself is ferrromagnetic, is also discussed.
Cosmological abundances of right-handed Dirac neutrinos
Kari Enqvist
Physics , 1996,
Abstract: The equilibration of the right-helicity states $\nu_+$ of light Dirac-neutrinos is discussed. I point out that the $\nu_+$ production rate is enhanced by weak gauge boson pole effects so that the right-helicity component of $\nu_\tau$ is brought into equilibrium at $T\simeq 10$ GeV independently of the initial abundance, provided $m_{\nu_{\tau}}\gsim 10$ keV. Neutrino spin flip in primordial magnetic fields and the resulting bound on $\mu_\nu$ is also discussed.
Aspects of Neutrino Cosmology
Kari Enqvist
Physics , 1993,
Abstract: Primordial nucleosynthesis constrains the properties of light, stable neutrinos. Apart from the well--known limit on the number of neutrino species, there are also bounds on neutrino masses and magnetic moments. I discuss also sterile neutrinos and neutrino propagation in a primordial magnetic field, such as could be the origin of the observed galactic magnetic fields.
Magnetic Fields in the Early Universe
Kari Enqvist
Physics , 1997,
Abstract: The observed galactic magnetic fields may have a primordial origin. I briefly review the observations, their interpretation in terms of the dynamo theory, and the current limits on cosmological magnetic fields. Several possible mechanisms for generating a primordial magnetic field are then discussed. Turbulence and the evolution of the microscopic fields to macroscopic fields is described in terms of a shell model, which provides an approximation to the full magnetohydrodynamics and indicates the existence of an inverse cascade of magnetic energy. Cosmological seed fields roughly of the order of $10^{-20}$ G at the scale of protogalaxy, as required by the dynamo explanation of galactic magnetic fields, seem rather plausible.
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