A summary of my prior reseach in need of updating is below:
Connecting Gravity, Time and Matter with Atomic Clocks
We find that an atomic clock in an elliptic orbit around the Earth
is sensitive to higher order relativistic effects
alternative theories of gravity .
At ground level, portable atomic clocks, can add detail to
satellite maps and help us in understanding the interior structure
of the Earth.
Gravitational Wave Astronomy: Stokes Parameters
I work on understanding our ability to measure gravitational wave polarization with
a given detector network. One can combine hp and hx in Stokes parameters that measure circular
and linear polarization. Circularly polarized gravitational waves carry angular momentul, while linearly polarized
waves do not. The degree of circular polarization is a measure of the nonaxisymmetry
of the source. This is particularly interesting for short and long Gamma ray burst phenomena,
where tracking the polarization of the gravitational waves could provide insight into the
evolution of the central engine. Polarization is a property of the radiation itself and
does not depend on the source model. This work is in collaboration with Sam Finn and Ravi Kopparapu, both
at Penn State University.
Resonant Shattering of Neutron Star Crusts
This is work in collaboration with David Tsang (Caltech), Jocelyn Read (Mississippi) and
Tony Piro (Caltech). We investigate the resonant excitation of neutron star modes by tides.
We find that the driving of the L=2, m=2 crust-core interface mode can lead to shattering of the
NS crust seconds before the merger of a NS-NS or NS-BH binary. This mechanism can lead to precursor
flares before short GRBs like the flares that have already been observed by Swift-BAT, Fermi and Suzaku.
We describe how a larger sample of precursor detections could be used alongside coincident gravitational
wave detections of the inspiral by Advanced LIGO class detectors to probe the NS structure.
These two types of observations nicely complement one another, since the former constrains the equation
of state and structure near the crust-core boundary, while the latter is more sensitive to the core equation of state.
My PhD thesis in collaboration with Profs. Saul Teukolsky and Ira Wasserman was on r-modes.
Rmodes are oscillations that occur in rotating fluids. In rapidly rotating neutron
stars these modes can be unstable. The instability is driven by the gravitational radiation reaction.
The most relvant mode for gravitational radiation emisson is the Rossby wave with L=m=2. This mode is
unstable when gravitational driving dominates viscous dissipation. Once the amplitude L=m=2 r-mode
passes its parameteric instability threshold amplitude, it excites other near-resonant modes in the system and
nonlinear effects become important. Roughly speaking, the r-mode instability converts
rotational energy to mode energy and gravitational radiation and the star slows down.
My current project is to understand how fast neutron stars can spin in LMXBs and
connect the limiting spin frequency due to r-modes to current observations.
Beams and mirror shapes for future gravitational wave interferometers.
Thermal noise will be the dominant form of noise in the most sensitive frequency band of Advanced LIGO detectors.
In the past, my collaborators and I investigated how finite mirror effects can affect the thermal noise of
non-Gaussian beams. We found some resonances that led to preferred beam widths with lower thermal noise for the
same diffraction loss. We showed that the coating thermal noise, which dominates in the most sensitive frequency
band of Advanced LIGO, can be reduced by 12% with no additional effort by using finite mirror
effects to our advantage rather then working against them and by 28% with some modifications to the mirror to
match the phase front of the finite beam. This work is in collaboration with Andrew Lundgren (Syracuse University/AEI Hannover),
David Tsang (Caltech) and Mihai Bondarescu (University of Mississippi).
Previous work by Mihai, Oleg Kogan and Yanbei Chen, in which they did not include finite mirror effects,
found that the optimal non-Gaussian mirror is conical and reduces thermal noise by 60% compared to Gaussian alternatives.
Luke-warm Dark Matter
Most matter in the universe is non-luminous. The observed flatness of the galactic rotation curves
has been an indicator of the presence of dark haloes around galaxies. More recently, gravitational
lensing observations of the Bullet cluster have provided direct proof of the presence of dark matter.
In collaboration with Andrew Lundgren (Syracuse U.), Mihai Bondarescu (the University of Mississippi)
and Jayashree Balakrishna (Harris Stowe State University), I work on understanding the cosmological
evolution and the Bose-Einstein condensation of ultra-light dark matter particles that have a Compton
wavelength of galactic dimensions. Agglomerations of these particles form stable halo structures that
are supported against collapse by Heisenberg's uncertainty principle similar to boson stars and naturally
exhibit no small scale structure. The particles that condense to the ground state behave like dust or
non-relativistic matter, while the particles in excited states act as radiation. Constraints on the
amount of radiation other than photons and neutrinos that can be present in the universe are
given by WMAP 7-year+BAO+H0 measurements. We found that a natural temperature for this condensate
would be around 0.9 K, which makes it luke-warm.
Other Exotic Dark Matter Candidates
In the past I studied compact scalar objects - boson stars (complex scalar field configurations; potential
particle candidates include WIMPs) and soliton stars (real scalar field configurations; the most prominent
scalar particles candidates are axions). Light axions could have been created by non-thermal
processes in the early universe leaving them slow moving and compatible with preferred cold-dark matter models.
Stars composed of scalar particles would be an exotic source of gravitational waves. Their detection would confirm
the presence of scalar field dark matter. We studied propreties of these stars using a 3D code based on the Cactus
Computational Toolkit (www.cactuscode.org), their stability under spherical
and non-spherical perturbations and the gravitational waveforms they produce.
This work has been done in collaboration with Jayashree Balakrishna (Harris Stowe University),
Gregory Daues (NCSA), Francisco S. Guzman (Universidad Michoacana de San Nicolas de Hidalgo, Mexico),
Mihai Bondarescu (AEI/Caltech/U. of Mississippi), and Ed Seidel (LSU/CCT). The luke-warm dark matter work
is a continuation of this work.
12. A. Scharer, R. Angelil R. Bondarescu , and P. Jetzer, "Testing Scalar-Tensor Theories and
Parametrized Post-Newtonian Parameters in Earth Orbit", Accepted to Phys. Rev. D.
11. R. Angelil, P. Saha, R. Bondarescu , P. Jetzer, A. Scharer, A. Lundgren,
"Spacecraft Clocks and Relativity: Prospects for Future Satellite Missions",
Phys. Rev. D89 , 064067 (2014). [arXiv:1402.6698]
10. R. Bondarescu, and I. Wasserman, "Nonlinear Development of the R-mode Instability
and the Maximum Rotation Rate of Neutron Stars",
Astrophys. Journal 778 , 9 (2013). [arXiv:1305.2335].
9. R. Bondarescu, M. Bondarescu, G. Hetenyi, L. Boschi, P. Jetzer,
J. Balakrishna, "Geophysical Applicability of Atomic Clocks: Direct Continental Geoid Mapping",
Geophysical Journal International 191, pages 78-92, 2012.
http://arxiv.org/abs/1209.2889. Description in the News.
8. D. Tsang, J. S. Read, T. Hinderer, A. L. Piro, and R. Bondarescu ,
"Resonant Shattering of Neutron Star Crusts",
Phys. Rev. Lett. 108 , 011102 (2012).
7. A. P. Lundgren, M. Bondarescu, R. Bondarescu and J. Balakrishna,
"Luke-warm dark matter: Bose condensation at finite temperatures. ", arXiv:1001.0051
ApJL 715 , L35 (2010).
6. R. Bondarescu, S. Teukolsky, and I. Wasserman,
"Spinning Down Newborn Neutron Stars: Nonlinear Development of the R-mode Instability",
arXiv:0809.3448 Phys. Rev. D 79, 104003 (2009).
5. A. P. Lundgren, R. Bondarescu , D. Tsang, M. Bondarescu,
"Finite Mirror Effects in Advanced Interferometric Gravitational Wave Detectors",
arxiv:0710.3808, Phys. Rev. D 77, 042003 (2008).
4. J. Balakrishna, R. Bondarescu , G. Daues, M. Bondarescu,
"Numerical Simulations of Oscillating Soliton Stars: Excited States in Spherical Symmetry and Ground State Evolutions in 3D",
Phys. Rev. D 77, 024028 (2008).
3. R. Bondarescu, S. Teukolsky, and I. Wasserman,
"Spin Evolution of Accreting Neutron Stars: Nonlinear Development of the R-mode Instability",
Phys. Rev. D 76, 064019 (2007).
2. J. Balakrishna, R. Bondarescu, G. Daues, F. Guzman, and E. Seidel,
"Evolution of 3D Boson Stars with Waveform Extraction",
Class. Quantum Grav. 23 (2006) 2631-2652,
1. R. Bondarescu, G. Allen, G. Daues, I. Kelley, M. Russell, E. Seidel, J. Shalf, M. Tobias,
"The Astrophysics Simulation Collaboratory Portal: a Framework for Effective Distributed
Future Generation Computing Systems
21 (2005) 259-270, Special Issue on Advanced Grid Technologies.
PDF version of the paper Abstract through Science Direct
Ruxandra Bondarescu, Cornell University, August 2008.
Articles about me
Interviu printre stele, Ziarul Timpul, Aprilie, 2011
Work in the Spotlight
1. The Geophysical Applicability of Atomic Clocks: Direct Continental Geoid Mapping work was featured
in the news.
A really good
decription of it can be found here. .
A spotlight of the work in German can be found here.
2. The resonant shattering of neutron stars work was spotlighted by Physical Review Letters as extraordinary research!
Read it here!
Some other news stories about this work can be found in
arstechnica and New Scientist.
This list is not up to date. I gave up posting all my talks in 2007.
See my CV for a more current seminar list.
1. "Rossby waves in neutron stars", CAM 2007, Montreal, Canada, August 2007,
(Travel Grant from APS)
2. "Spin Evolution of Accreting Neutron Stars and the R-mode Instability",
GR18, Australia, July 2007 (ICPS travel grant + Cornell Travel Grant + NSF travel grant).
3. "Spin Evolution of Accreting Neutron Stars: Nonlinear Effects of the R-mode Instability", East Coast Gravity Meeting and The Teukolsky Birthday Symposium,
Cornell, June 2007 (free; I also chaired a session ).
4. "Spin Evolution of Neutron Stars: Nonlinear Effects of the R-mode Instability", April APS Meeting, Florida, 2007 (Travel Grant from both Cornell and APS)
5. "R-modes in Spinning neutron stars", International Conference for Physics
Students, Bucharest, Romania, August 2006.
6. "How fast can neutron stars spin?", CAM 2005 (Travel grant awarded by APS that covered all expenses)
7. "Evolution of 3D boson stars", April APS Meeting 2004, Tampa, Florida (Travel grant awarded by APS to attend this conference)
8. "Boson Stars", East Coast Gravity Meeting, March 2003
9. "Introduction to Boson Stars", West University of Timisoara (invited talk)
Old computer science talks
1. "Requirements for Grid Enabling an Application", presented at the GAT Workshop, Cardiff University,
United Kingdom, July 2003 Slides
2. "The Astrophysics Simulation Collaboratory Portal", presented at the GridLab All Hands conference and
workshop, Eger, Hungary, April 2003
3. "The ASC Portal: A Tool for Numerical Relativity", presented at Louisiana State University,
4. "Grid and Portal Technology Tutorial", presented at West University of Timisoara, Romania, March,
5. "Short overview of research activities at the LSU CAPITAL + Short Cactus Tutorial",
presented as part of the Gravitational Waves Fun - Louisiana State University,
January, 2004 (Slides)
Teaching and TAing
Physics 217 - Electricity and Magnetism for Honor Students: Spring 2005 (part time TA) with Prof. Lois Pollack, Fall 2005 (full time TA) with Prof. Andre Leclair
- My brother and I organized a series of 14 Gravitational Waves lectures at LSU (December 03-January 04) based
on Kip Thorne's Ph. 237. We received funding from LSU CAPITAL to organize the lectures.
I organized the last 4 lectures after Mihai left with help from Greg. We did the same thing
at Cornell in the Spring of 2004 (and for part of the summer) and here I was the main organizer.
Gravitational Waves Fun at Cornell - Spring 2004
Gravitational Waves Fun at LSU - Winter 2003
- Department of Physics, University of Illinois at Urbana-Champaign, IL
Course: Physics 371 (Advanced Optics- Light)
Professor: Taekjip Ha
Course: Physics 140 (Practical Physics: How Things Work)
Professor: Laura H. Greene
- Teaching Assistant
Course: Physics 114 (General Physics: Waves and Quantum Mechanics)
Professor: Gary Gladding and Lance Cooper
MaxEnt files: Sam's Extrig Talk.
The Penn State Gravitational Waves Group website http://www.gwastro.org.
These are two webpages with pics from boson star simulations. They were primarly written to convince
my undergraduate advisor that we had enough for a paper and it worked :).
Boson Star Results (Last Updated Jan 25, 2004)
Older Webpage with Results (Last Updated Dec 1, 2003)