H. Tam

University of Florida

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Qiaoli Yang

Jinan University

Ozgur Erken

University of Florida

P. Sikivie

University of Florida

D. Price

Lawrence Livermore National Laboratory

K. Widmann

Lawrence Livermore National Laboratory

Tommy Ao

Sandia National Laboratories

A. Ng

University of British Columbia

Y. Ping

Lawrence Livermore National Laboratory

P. T. Springer

Lawrence Livermore National Laboratory

A. Lavidis Nickolas

Cooperative Institutions

Lawrence Livermore National Laboratory

University of British Columbia

University of California, Berkeley

University of California, Davis

Los Alamos National Laboratory

University of Rochester

Energetics (United States)

Massachusetts Institute of Technology

General Atomics (United States)

Applied Energetics (United States)

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Gravitational Field Inside and Near a Caustic Ring

arXiv (Cornell University) (2012)

H. Tam

We present an analytic calculation of the gravitational field inside and near a caustic ring of dark matter. The calculation may facilitate N-body simulation studies on the effects that dark matter caustics have on galaxy formation.

Caustic (mathematics)

Gravitational potential

10.48550/arxiv.1205.1260

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Axion Dark Matter and Cosmological Parameters

Physical Review Letters (2012)

Ozgur Erken P. Sikivie H. Tam Qiaoli Yang

We observe that photon cooling after big bang nucleosynthesis (BBN) but before recombination can remove the conflict between the observed and theoretically predicted value of the primordial abundance of $^7$Li. Such cooling is ordinarily difficult to achieve. However, the recent realization that dark matter axions form a Bose-Einstein condensate (BEC) provides a possible mechanism, because the much colder axions may reach thermal contact with the photons. This proposal predicts a high effective number of neutrinos as measured by the cosmic microwave anisotropy spectrum.

10.1103/physrevlett.108.061304

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Citations (45)

Axion BEC Dark Matter

arXiv (Cornell University) (2011)

Ozgur Erken P. Sikivie H. Tam Qiaoli Yang

Cold dark matter axions thermalize through gravitational self-interactions and form a Bose-Einstein condensate when the photon temperature reaches approximately 500 eV. Axion Bose-Einstein condensation provides an opportunity to distinguish axions from the other dark matter candidates on the basis of observation. The rethermalization of axions that are about to fall in a galactic potential well causes them to acquire net overall rotation, whereas ordinary cold dark matter falls in with an irrotational velocity field. The inner caustics of galactic halos are different in the two cases.

Cold dark matter

Light dark matter

Thermalisation

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Warm dense matter created by isochoric laser heating

Yongli Ping Alfredo A. Correa Tadashi Ogitsu Erik W. Draeger Eric Schwegler

Isochoric process

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Cosmic axion thermalization

Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D, Particles, fields, gravitation, and cosmology (2012)

Ozgur Erken P. Sikivie H. Tam Qiaoli Yang

Axions differ from the other cold dark matter candidates in that they form a degenerate Bose gas. It is shown that their huge quantum degeneracy and large correlation length cause cold dark matter axions to thermalize through gravitational self-interactions when the photon temperature reaches approximately 500 eV. When they thermalize, the axions form a Bose-Einstein condensate. Their thermalization occurs in a regime, herein called the ``condensed regime,'' where the Boltzmann equation is not valid because the energy dispersion of the particles is smaller than their interaction rate. We derive analytical expressions for the thermalization rate of particles in the condensed regime, and check the validity of these expressions by numerical simulation of a toy model. We revisit axion cosmology in light of axion Bose-Einstein condensation. It is shown that axions are indistinguishable from ordinary cold dark matter on all scales of observational interest, except when they thermalize or rethermalize. The rethermalization of axions that are about to fall in a galactic potential well causes them to acquire net overall rotation as they go to the lowest energy state consistent with the total angular momentum they acquired by tidal torquing. This phenomenon explains the occurrence of caustic rings of dark matter in galactic halos. We find that photons may reach thermal contact with axions and we investigate the implications of this possibility for the measurements of cosmological parameters.

Cold dark matter

Thermalisation

10.1103/physrevd.85.063520

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Citations (129)

The Color of High Energy Density Gold

IEEE conference record-abstracts (2005)

Y. Ping Tommy Ao H. Tam K. Widmann D. Price

Summary form only given. The study of non-equilibrium phase transitions is a rapidly developing field. Non-thermal melting has been observed in femtosecond laser heated semiconductors such as silicon. This is thought to result from the excitation of valence electrons to the conduction band, giving rise to anti-bonding states. In metals, the process of melting under ultrafast laser excitation is not clearly understood. In our experiment, we measure the broadband (400-800 nm) optical reflectivity and transmissivity of freestanding, 30 nm-thick gold foils heated with 150 fs, 400 nm laser light. Prior to laser excitation the sample shows strong reflectivity for wavelengths above 500 nm. This is due to interband (d to s/p) transitions, thus giving gold its characteristic color. The reflectivity and transmissivity spectra of the heated sample (hence the color of gold) change substantially with laser excitation energy densities. Such spectral signatures offer a new means of probing electronic and structure behaviors associated with non-equilibrium phase transitions

10.1109/plasma.2005.359204

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Cosmic Ray Protons Illuminate Dark Matter Axions

arXiv (Cornell University) (2011)

H. Tam Qiaoli Yang

Cosmic ray protons propagating in a spatially-homogeneous but time-dependent field of axions or axion-like particles (ALPs) emit photons in a way that is reminiscent of Cherenkov radiation by charged particles in a preferred background. We compute the emission rate and energy spectrum of the photons, and discuss the possibility of their detection using the Square Kilometre Array which is currently under construction. In the case of a non-detection, constraints can be placed on the parameter space of ALPs whose mass lie between $10^{-7}$eV and $10^{-5}$ eV under the assumption that they are the primary constituent of dark matter.

10.48550/arxiv.1108.3362

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Laser-induced nonequilibrium solid-to-plasma phase transition in ultrathin gold foils

APS (2004)

Yongli Ping Tommy Ao H. Tam K. Widmann D. Price

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Axion BEC Dark Matter

Ozgur Erken P. Sikivie H. Tam Qiaoli Yang

Cold dark matter axions thermalize through gravitational self-interactions and form a BoseEinstein condensate when the photon temperature reaches approximately 500 eV. Axion Bose-Einstein condensation provides an opportunity to distinguish axions from the other dark matter candidates on the basis of observation. The rethermalization of axions that are about to fall in a galactic potential well causes them to acquire net overall rotation, whereas ordinary cold dark matter falls in with an irrotational velocity field. The inner caustics of galactic halos are different in the two cases.

Cold dark matter

Light dark matter

Mixed dark matter

10.3204/desy-proc-2011-04/sikivie_pierre

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Warm dense matter created by isochoric laser heating

High Energy Density Physics (2010)

Y. Ping Alfredo A. Correa Tadashi Ogitsu Erik W. Draeger Eric Schwegler

Isochoric process

Warm dense matter

State of matter

10.1016/j.hedp.2009.12.009

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Citations (33)