Research

My interdisciplinary background in mathematics, physics and computer science has directed my research in accelerator physics and astrophysics. 

Inverse Compton Sources of X-Ray Radiation

In recent years, I have been using state-of-the-art mathematical techniques and computational architectures to advance our ability to simulate and optimize particle accelerators. In particular, my research focuses on the inverse Compton sources (ICS) of x-ray radiation because of their societal impact. X-rays enable scientists to see the internal structure of materials on all length scales from the macroscopic down to the positions of individual atoms. This capability has had a profound impact on science, technology, and on the world economy. It is impossible to overestimate this impact—from Nobel Prize winning science to the everyday dental x-ray. The science and technology community agrees that future advances in many areas depend on understanding structure/function relationships at the nano-scale where new properties emerge, and controlling the fabrication of complex materials at that scale to achieve transformative physical, chemical, and biological functionality. Hence x-rays can have a huge role to play in future scientific advancement in these fields.

ICS of x-ray radiation utilizing relativistic electrons have seen increased use in fundamental physics research in the recent years. The small frequency bandwidth of the scattered radiation is highly desirable for applications in nuclear physics, medicine and homeland security. Brightness of the emitted radiation is directly proportional to the intensity of the laser pulse. As the intensity of the incident laser pulse increases, the deleterious non-linear effects start to emerge: (i) the bandwidth of the emitted radiation grows, scattering photons to experimentally useless energies; and (ii) the rate of increase in peak spectral brightness slows down.  We have recently shown that a judicious frequency modulation of the laser pulse can completely counteract these unwanted non-linear effects in ICS (Terzić et al. 2014; Terzić & Krafft 2016; Terzić et al. 2021; Krafft et al. 2023). This groundbreaking technique promises to substantially extend the science reach of ICS operating in the high laser field regime.

We have recently advanced the state of the art in the field of simulating radiation from ICS by:

• Generalizing the frequency modulation to Compton regime when electron recoil may not be neglected (Krafft et al. 2016; Ranjan et al. 2018; Terzić et al. 2021; Krafft et al. 2023) 

• Generalizing the 1D plane-wave to the 3D pulse model for the laser pulse (Maroli et al. 2018; Terzić et al. 2019; Johnson et al. 2022);

• Improving performance of ICS by avoiding non-linearities (Terzić et al. 2020).

• Simulating the existing and future light sources (Deitrick et al. 2018; Deitrick et al. 2021).

Our current efforts focus on:

• Using an alternative, statistical approach to improve the efficiency of computations of radiation spectra by possibly three orders of magnitude. This level of improved efficiency of our codes would extend their science reach, and possibly make them a real-time operational tool.

• Reverse-engineering the experimental configuration from the emitted spectra, thereby making the simulations a diagnostic tool. This approach would lead to substantial savings in expensive electronic diagnostic hardware.

• Combine our codes with genetic algorithms to optimize the performance of existing and future ICS.

• Understanding the effect of strong laser fields on electron energy loss during the inverse Compton scattering, the problem known as radiation reaction. This is one of the oldest and most important open problems in accelerator physics.

High-Performance Simulations of Coherent Synchrotron Radiation

When the electron bunches are forced to traverse a curved trajectory, they emit bright ultraviolet or x-ray radiation. The electron machines which produce such radiation, called synchrotron light sources, are powerful tools for cutting edge research in physics, biology, chemistry, energy, medicine and other fields. As the brightness and energy of these synchrotron light sources is extended beyond present levels, it becomes necessary to develop new computational modeling capabilities. One of the most critical needs is to develop efficient computer codes for simulating collective effects that severely degrade beam quality, such as coherent synchrotron radiation (CSR) and CSR-driven micro-bunching instability (Terzić & Bassi 2011).

We have developed an innovative code for high-performance simulations of synchrotron light sources which uses massively parallel computation on graphical processing units (GPUs) (Arumugam, Godunov, Ranjan, Terzić & Zubair 2013a, 2013b, 2016; Arumugam et al. 2017) and wavelet methodology (Terzić, Pogorelov & Bohn 2007; Bohn et al. 2006). 

We also designed and deployed an algorithm for adaptive, multidimensional numerical integration optimized to run on GPUs (Sakiotis, Arumugam, Paterno, Ranjan, Terzić & Zubair 2021, 2022).

Using Genetic Algorithms for Optimization in Accelerator Physics

Accelerator physics deals with intricate systems which depend on many interrelated specifications/variables and physical quantities. One of its main goals is to design and operate accelerators so as to achieve an efficient interplay between these many quantities, thereby optimizing their performance. This is why genetic algorithms (GAs)—efficient, robust, multidimensional nonlinear optimization tools—are crucially important.

We implemented a parallel GA paradigm and applied it to a number of problems in accelerator physics, demonstrating that many previously intractable problems are now well within reach of GA optimization (Hofler et al. 2013; Terzić et al. 2014). 

In a recent study, we also showed that solving a large subset of multidimensional nonlinear optimization problems can be significantly improved by decoupling their intrinsically linear and nonlinear parts (Cotnoir & Terzić 2016).

Simulations of Long-Term Collective Effects in Particle Colliders

Long-term simulation of the beam dynamics for millions or billions of turns in a storage ring or a collider are a direct way to validate the dynamical stability of the ring's design. This is highly desirable for the design and optimization of existing and figure storage rings and colliders, such as LHC, RHIC, LHeC and electron-ion colliders. However, such long-term simulations have been prohibitive due to their heavy computational load. Various techniques of estimating the long-term dynamical stability based on relatively short-term simulations may not provide the necessary level of confidence. One particular complication of simulating collider beam dynamics is the necessity to account for the beam-beam interaction, which is an integral part of the collider dynamics and must be solved for each bunch crossing, with the solution coming at the high computational cost. 

We are developing algorithms specifically crafted to exploit fully the massive parallelism offered by the modern GPUs, thereby rendering the long-term beam-beam simulations tractable (Arumugam et al. 2017).

Astrophysics & Cosmology

My astrophysics group at Old Dominion University and I have been investigating the role that non-linearity plays in general relativity (GR). Can properly accounting for non-linearities, usually neglected when analyzing the Universe, lead us toward uncovering the nature of the two most important mysteries in physics: dark matter and dark energy?

The discrepancy between the visible mass in galaxies or galaxy clusters, and that inferred from their dynamics is well known. The prevailing solution to this problem is dark matter. In a recent study, we showed that a different approach, one that conforms to both the current Standard Model of Particle Physics and GR, explains the recently observed tight correlation between the galactic baryonic mass and its observed acceleration. Using direct calculations based on GR's Lagrangian, and parameter-free galactic models, we showed that the non-linear effects of GR make baryonic matter alone sufficient to explain this observation (Deur, Sargent & Terzić 2020).

One of the most important problems vexing the ΛCDM cosmological model is the Hubble tension. It arises from the fact that measurements of the present value of the Hubble parameter performed with low-redshift quantities, e.g. the Type IA supernovae, tend to yield larger values than measurements from quantities originating at high-redshift, e.g. fits of cosmic microwave background radiation (CMB). It is becoming likely that the discrepancy, currently standing at 5σ, is not due to systematic errors in the measurements. We explored whether the self-interaction of gravitational fields in GR, which are traditionally neglected when studying the evolution of the Universe, can contribute to explaining the tension. We found that with field self-interaction accounted for, both low- and high-redshift data are simultaneously well-fitted, thereby showing that gravitational self-interaction yield consistent values for the Hubble parameter when inferred from Type IA supernovae and CMB observations. Crucially, this is achieved without introducing additional parameters (Sargent, Deur & Terzić 2024).

We examine the claimed observations of a gravitational external field effect (EFE) reported by Chae et al. We show that observations suggestive of the EFE can be interpreted without violating Einstein’s equivalence principle, namely from known correlations between the morphology, the environment, and dynamics of galaxies. While Chae et al.’s analysis provides a valuable attempt at a clear test of modified Newtonian dynamics, an evidently important topic, a re-analysis of the observational data does not permit us to confidently assess the presence of an EFE or to distinguish this interpretation from that proposed in this article (Sargent et al. 2025).

When CMB radiation scatters off hot intracluster electron gas, it results in a small, yet measurable shift in the CMB photons distribution. This effect is called the Sunyaev-Zel’dovich effect (SZE).  We are currently working on developing the first fully and inherently relativistic derivation of the thermal SZE. The novel approach employs the formalism historically used to compute radiation spectra emerging from ICS of x-ray radiation. Comparing our results to the traditional approach, we find small, but systematic differences. Most notable are the modest (< 10%) differences in the crossover frequency where the spectral distortion due to the SZE vanishes, and the energy increase of the distribution at high electron cloud temperatures (Terzić et al. 2024).

In the past, I have worked on a number of other astrophysical problems. Here are some of them:

• • Structure of dark matter galactic halos (Merritt et al. 2006; Graham et al. 2006a; Graham et al. 2006b)

  • Destabilizing effects of supermassive black holes at the centers of galaxies (Terzić 2002; Kandrup et al. 2003; Terzić & Kandrup 2004)

  • Realistic elliptical galaxy models (Terzić & Graham 2006; Terzić & Sprague 2007)

  • Role of chaos in galaxy evolution (Terzić 2002; Kandrup et al. 2003; Terzić & Kandrup 2003; Terzić & Kandrup 2004)