
Faculty :
Lara Anderson,
Lay Nam Chang,
James Gray,
Shunsaku Horiuchi,
Patrick Huber,
Djordje Minic,
Eric Sharpe,
Tatsu Takeuchi
Emeriti Faculty :
Tetsuro Mizutani,
Chia Tze
Reasearch Faculty/Postdoctoral Associates :
John “JJ” Cherry,
Xin Gao,
SeungJoo Lee,
Oscar Macias,
David Vanegas
Graduate Students :
Jonathan Baker,
Zhuo Chen,
Wei, Cui,
He Feng,
Wei Gu,
Jirui Guo,
Patrick Jaffke,
Mohsen Karkheiran,
Hadi Parsian,
Chen Sun,
Juntao Wang,
Ruoxu Wu
Visiting Graduate Students :
Kimiko Yamashita (Fall 2015)
Graduate students interested in joining our group should come talk to us immediately upon their arrival at Tech
and receive guidance on what courses they should take. RA support is also very limited so students are only supported
on a first come first serve basis; it is imperative that you put your name on the waiting list as early as possible.
The Theoretical Particle Physics & String Theory group at Virginia Tech
is working on a wide range of problems addressing the fundamental nature of the
universe and its constituents.
Our current knowledge of elementary particles and their interactions can be summarized in the chart shown here.
There exist 6 flavors of quarks (u, d, s, c, b, t, in the order of discovery) and 6 flavors of leptons (e, μ, ν_{e}, ν_{μ}, τ, ν_{τ}, again in the order of discovery) which interact with each other through the exchange of the force carrier particles. All the quarks couple to γ (photon), g (gluon), Z, and W, while the charged leptons (e, μ, and τ) couple to γ, Z, and W, and the neutrinos (ν_{e}. ν_{μ}, and ν_{τ}) only couple to the Z and the W.
The behavior of these particles are well described by a local quantum field theory known by the rather unimaginative name of the Standard Model. However, the Standard Model has many arbitrary parameters in it, and moreover is unstable under quantum corrections. Various attempts exist to understand the Standard Model better, for instance, to derive it from a more fundamental theory such as String Theory (Anderson, Gray, Sharpe, Minic), and to better determine the particles' properties from experimental and astronomical data (Horiuchi, Huber, Takeuchi).

Anderson's research focuses on various aspects of geometry and particle phenomenology in string theory. Recently she has been working on developing tools to link string theory to experimental results in particle physics and cosmology. Her work includes compactifications of heterotic string theory, Mtheory and Ftheory. She hopes to build a better understanding of the low energy effective physics of string theory, using tools from algebraic geometry (including computational algebraic geometry).

Prof. Anderson (right) explains string theory to a graduate student.

Prof. Gray (left) explains string theory to a graduate student.

Gray's research focuses on various aspects of string phenomenology  the attempt to link string theory to experimental particle physics and cosmology. His work concentrates on compactifications of the heterotic string and Ftheory, as these are the constructions which can reproduce the successes of Grand Unified physics (without some of the problems) in a string theory context. Technically, Gray uses a lot of geometrical methods and tools from computational commutative algebra in order to describe the complicated spaces which appear in these solutions of string theory.

Horiuchi's group is interested in using highenergy astronomical messenger particles to study the nature of particle dark matter. The current cosmological paradigm requires that dark matter dominate over "normal" baryonic matter. Dark matter does not fit in the Standard Model of particle physics and must arise from some new beyondthestandardmodel physics. Although dark matter particles need to be largely stable, in many theoretical models they can decay or annihilate. The group is interested in theoretical models of dark matter, how their particle properties manifest in complex astrophysical and cosmological signal, and developing techniques to disentangle dark matter signals from astrophysical backgrounds.

Prof. Hoiuchi (right) and Dr. Cherry (left) discussing an astrophysics problem.

Prof. Huber (center) working with his students on the phenomenology of neutrinos.

Huber has studied the potential offered by a number of proposed new neutrino experiments to discover a nonzero mixing angle
θ_{13} and to explore leptonic CP violation. The
focus of his research was on numerical methods to accurately and
efficiently predict physics sensitivities of yet to be built experiments.
He works closely with the VT experimental neutrino science group and is himself a member of the Daya Bay Collaboration.
Neutrinos are the unique probe of physics not
accessible by accelerators like the Large Hadron Collider, and
therefore improving our knowledge about neutrinos is highly
complementary to traditional collider physics.

Minic has been concentrating his effort on understanding how the quarks and gluons (particles in the upper half of the chart) interact with each other to form baryons, mesons, and glueballs. Baryons are a class of particles that comprise the proton and the neutron which are the basic building blocks of atomic nuclei. Understanding how they are formed from quarks will be a major breakthrough in our understanding of what we are made of.

Prof. Raghavan (left, neutrino science experimentalist) and Prof. Minic (right) discuss the timeenergy uncertainty relation, November 3, 2009.

Prof. Sharpe (left) working with a student on an intricate math problem associated with String Theory.

Sharpe has been interested in understanding what quarks, gluons, and the other particles in the chart above are made of. Together with Anderson, Gray. and Minic, he works on various problems in string theory, one current attempt to reconcile particle physics and general relativity. String theory says that each of the particles in the chart above can be understood as a vibration of a onedimensional object, known as a string. Furthermore, many developments in string theory have had spinoffs which gave more direct insight into particle physics, for example the understanding of strong coupling physics in certain ("supersymmetric") models of quarks and gluons. Although string theory is not directly testable experimentally, there are many indirect tests that can be performed via, for example, the mathematical predictions of string theory, and so he is also interested in mathematical aspects of the subject.

Takeuchi has been interested in figuring out what can be inferred about new physics (particles and interactions that are yet to be discovered) from precision measurements of how the Z and W interact with the quarks and leptons. Most recently, he has been looking at how one flavor of neutrino changes into another (neutrino oscillations) in the presence of matter, and studying what an experimental measurement of the process can potentially tell us about the unknown.
Together with Minic, he is also studying the application of noncommutative geometry to particle physics model building.

Prof. Takeuchi (right) discussing a problem over tea with 2008 Nobel Laureate Dr. Yoichiro Nambu (left) at a workshop in Nagoya, Japan, December 2002.

Prof. Minic (right) discussing a condensed matter physics problem with Profs. Scarola, Heremans, and Park.

In addition to string theory, Minic and Sharpe work together on various fundamental problems quantum gravity and cosmology. Takeuchi also works on dark matter and baryogenesis. The group also works closely together on a variety of different topics such as the foundations of quantum mechanics, and quantum computing. Minic also works with members of the condensed matter physics group on applying string theory techniques to a variety of condensed matter physics problems.

Graduate students working on phenomenology are encouraged to present a talk at the annual
PHENO symposium at the University of Pittsburgh,
in addition to various opportunites available on campus to showcase their research.

Graduate Student Eric Christensen presents a talk on sterile neutrinos at Pheno 2011 at the University of Wisconsin Madison, May 10, 2011


During the summer, students are sent to summer schools such as the Theoretical Advanced Studies Institute (TASI) at the
University of Colorado, Boulder,
the SLAC Summer Institute (SSI) at
the Stanford Linear Accelerator Center in California,
the Prospects in Theoretical Physics (PiTP) program at the Institute of Advanced Studies in Princeton, New Jersey,
the CERNFermilab Hadron Collider Physics Summer School which alternates
between Geneva, Illinois and Genève, Switzerland,
and
the Cargèse Summer School on Corcica.

The group is supported by a generous donation from Mr. Mark Sowers, and by research grants from the DOE and the NSF.

Prof. Takeuchi (center) discussing a problem with Prof. Oonogi of Osaka University (right) and 2008 Nobel Laureate Dr. Toshihide Maskawa (left) at a workshop in Nagoya, Japan, December 2009.

