UNIVERSITY OF FLORIDA HIGH ENERGY THEORY STUDENT GROUP JOURNAL CLUB

These meetings are informal discussions of topics of our interest which should normally last one to one and half hours. Individual research talks are of course welcome, although we would like to encourage speakers to give presentations about more general topics that can be of a broader interest for all of us since we are a small group.

Our talks take place on Tuesdays at 4:00 pm in Room 2165 (IFT room)
Contact: Francisco Rojas frojasf@phys.ufl.edu
Sample Topics UF Physics Calendar

FALL 2010

AUGUST 31
	Speaker	All
	Title	First semester meeting: General Discussion.

SPRING 2010

APRIL 13
	Speaker	Brian Williams
	Title	A Soluble Quantum Field Theory in d = 1+1.
	Abstract	In the majority of quantum field theories we have studied we must revert to perturbation theory at some level to obtain the correlation functions. In this talk I give an example of a completely soluble field theory which we can write down explicit correlation functions without the use of perturbation methods. The theory is called the (massless) Thirring Model and it describes a self interacting Dirac fermion in one space and one time dimension. The main problem one runs into with this model is in the definition of the current. We will find a covariant definition of the current, and then go on to evaluate correlation functions via the external field approach. Time permitting, I can talk about the massive generalization of the Thirring model and how this turns out to be S-dual to the Sine-Gordon model.
	References	C.M. Sommerfield, Ann. of Phys. 26 (1963). S. Coleman, Phys. Rev. D11, 8 (1975). P. Ramond. "Field Theory: A Modern Primer" 2nd Edition.

APRIL 6
	Speaker	Tongguang Cheng
	Title	MHV Amplitudes and Twistor Space
	Abstract	Starting from a Lagrangian, we can write down the Feynman rules and then calculate any S-matrix element (or amplitude) to any order in the coupling constants in principle. Symmetries in the Lagrangian will be reflected on S-matrix elements. We can also think of the symmetry of the S-matrix arising from a Lagrangian. An MHV amplitude is such an example. On the other hand, MHV amplitudes have a quite simple form in twistor space which can be thought of as a complex version of the regular space time. The idea can also be generalized to the Supersymmetric case. For maximal Susy (N=4), the (tree) amplitudes in the super twistor space can be constructed using only symmetry considerations, indicating its counterpart for a String Theory. I'll with restrict my talk though to the quantum field theory part only.
	References	arXiv:hep-th/0504194 "Lectures on twistor strings and perturbative Yang-Mills theory" arXiv:0808.1973 "MHV Lagrangians for Yang--Mills and QCD" arXiv:0903.2110 "The S-Matrix in Twistor Space" arXiv:0808.1446 "What is the Simplest Quantum Field Theory?"

MARCH 23
	Speaker	Jay Perez
	Title	An Introduction to Conformal Field Theory in 2 Dimensions (Part 2)
	Abstract	Here we will continue with our previous talk
	References	"Conformal Field Theory" by Di Francesco P. Mathieu P., Senechal D. "Applied Conformal Field Theory" by Paul Ginsparg arXiv:hep-th/9108028v1 "Lectures on String Theory" by D. Lust and S. Theisen

FEBRUARY 23
	Speaker	Jay Perez
	Title	An Introduction to Conformal Field Theory in 2 Dimensions
	Abstract	In this talk I will give an introduction to the Conformal group in first D dimension and later specializing to D = 2. I will go over topics such as the Virasoro generators, primary fields, and the Operator Product Expansions. Time permitting, the ideas of Radial Quantization and Hilbert space for CFT's will be discussed.
	References	"Conformal Field Theory" by Di Francesco P. Mathieu P., Senechal D. "Applied Conformal Field Theory" by Paul Ginsparg arXiv:hep-th/9108028v1 "Lectures on String Theory" by D. Lust and S. Theisen

FEBRUARY 2
	Speaker	Sohyun Park
	Title	The Graviton Self-Energy during Inflation
	Abstract	I study the effects of the graviton self-energy at one loop order in de Sitter background. Using quantum gravity as an effective field theory, I try to see how the one loop correction due to highly infrared virtual particles produced during inflation changes dynamical gravitons and the force of gravity.
	References

FALL 2009

DECEMBER 8
	Speaker	Jesus Escobar
	Title	A Flavor Model with Finite Group Delta(54)
	Abstract	A Flavor model has been investigated using the finite group Delta(54). The aim of the model is to provide an explanation for the large angles found in the lepton mixing matrix. Here we present some of the work that has been done so far using Delta(54).
	References	J. A. Escobar and C. Luhn, J. Math. Phys. 50, 013524 (2009)

DECEMBER 1
	Speaker	Roberto Vidal (UAM, Spain)
	Title	Quantum Field Theory in Curved Spacetime: A brief introduction.
	Abstract	Quantum field theory in curved spacetimes is the appropriate tool to describe the quantum effects of matter in the presence of gravitational fields, just as black holes or the expanding universe. I will illustrate the very basic formalism through the most simple case (a 1+1 expanding universe).
	References	L.H. Ford: gr-qc/9707062v1 N. D. Birrell, P. C. W. Davies, Quantum Fields in Curved Space (Cambridge Monographs on Mathematical Physics)

NOVEMBER 24
	Speaker	Gaurab Sarangi
	Title	Gravitons in the large extra-dimensions scenario
	Abstract	It has long been proposed that additional spatial dimensions can exist in nature. Eventually it was realized some scenarios with extra-dimensions like Large Extra Dimensions or Randall-Sundrum type models can also say something on the much talked Hierarchy problem. In these models the Standard Model is only confined to our (3+1) dimension brane whereas (unlike the Universal Extra-Dimension scenario) only Gravitons can propagate everywhere including the extra-dimension. I'll discuss some of the theoretical framework on this model before describing possible collider signatures which can be looked at the LHC to discover extra-dimensions and gravitons.
	References	G. Gabadadze: hep-ph/0308112v1

NOVEMBER 17
	Speaker	Francisco Rojas
	Title	Introduction to String Theory (Part 1)
	Abstract	We will start with quantizing the classical string (open and closed) and derive the spectrum described by its quantum states. On the way we will show how this process restricts the number of space-time dimensions to a critical value. We will take a closer look at the closed string spectrum and show why it has the potential to describe Einstein's General Relativity as a low energy effective theory. We will continue (probably in the second part) with a formulation that includes fermions and show how this more complete theory is a supersymmetric one. We will finish with the construction of string scattering amplitudes and show how the low energy limit describes a Yang-Mills Theory.
	References	"Lectures on String Theory", D.Lüst and S. Theisen "Superstring Theory" Vol.1 , M. Green, J. Schwarz and E. Witten.

NOVEMBER 10
	Speaker	Sohyun Park
	Title	The invariant volume of past light-cone and Paneitz Operator (Part 2)
	Abstract	Here we will continue last week's talk.
	References	S. Park and R. Woodard gr-qc/0910.4756

NOVEMBER 3
	Speaker	Sohyun Park
	Title	The invariant volume of past light-cone and Paneitz Operator (Part 1)
	Abstract	I will talk about a conjecture involving the volume of past light-cone. The conjecture is that a 4th order differential operator called the Paneitz operator which occurs in the theory of conformal anomalies gives a constant when acted upon the volume of the past light-cone. I will show that the conjecture is valid for an arbitrary homogeneous, isotropic and spatially flat geometry (FRW geometry) and briefly go over the fact that a perturbation about flat spacetime reveals a violation of the conjecture which, however, vanishes for any vacuum solution of the Einstein equation. This talk is based on my recent research. However, I will try to avoid too many technical details and give you general ideas how we can use general relativity for real problems which was actually my personal motivation on this project.
	References	S. Park and R. Woodard gr-qc/0910.4756

OCTOBER 6
	Speaker	Tongguang Cheng
	Title	Dirac, Weyl and Majorana Spinors
	Abstract	In this talk we develop a summary of the properties of Weyl, Majorana and Dirac spinors together with their corresponding mass terms and the symmetries of the Lagrangians built out of them.
	References	Ramond P. "Field Theory: A Modern Primer" 2nd Edition, Chapter 1 S. Weinberg, "The Quantum Theory of Fields" Vol. 1 Chapter 5

SEPTEMBER 29
	Speaker	Alejandro Quintero-Cabra
	Title	Spinors in Higher Dimensions (Special Time: 2:00pm)
	Abstract	Spinors in dimensions higher than four are very commonly used. In this talk I review some basic facts about Lie groups and representation theory and build up the spinor representation of the Lorentz Group O(d-1,1) in an arbitrary spacetime dimension.
	References	S. Weinberg, "The Quantum Theory of Fields" Vol. 3 Appendix J. Polchinski, "String Theory" Vol. 2 Appendix B.1

SEPTEMBER 15
	Speaker	Francisco Rojas
	Title	The Large N Limit of Quantum Field Theories (Part 2)
	Abstract	We continue last week's talk by introducing t' Hooft's double line formalism and derive a topological expansion for the sum of Feynman diagrams, where 1/N is the expansion parameter. Along these lines we show that the leading terms correspond to planar diagrams. The connection between this expansion and string theory is also discussed.
	References	G. t' Hooft, Nucl.Phys.B72:461,1974

SEPTEMBER 8
	Speaker	Francisco Rojas
	Title	The Large N Limit of Quantum Field Theories
	Abstract	The large N limit is one the most concrete possibilities for understanding confinement and the non-perturbative aspects of the field theories that exhibit these properties. QCD is one of them. In this talk I review this limit in terms of the 1/N expansion as originally proposed by t' Hooft and other examples where it has been applied since then.
	References	S. Coleman "1/N", Erice Lectures 1979 G. t' Hooft, Nucl. Phys. B72 (1974) 461

SEPTEMBER 1
	Speaker	Prof. Richard Woodard
	Title	The Theorem of Ostrogradsky or Why Newton Was Right
	Abstract	I work out the canonical formalism of Lagrangians that depend non-degenerately upon higher time derivatives. One consequence is that each extra higher derivative induces a new degree of freedom with a kinetic energy of alternating sign. For interacting, continuum field theories this induces instabilities of such virulence that most higher derivatives are ruled out.
	References	R.P. Woodard astro-ph/0601672 Sections 2 and 3

AUGUST 25
	Speaker	Jay Perez
	Title	A Review of General Relativity: Einstein's Equation and the Einstein-Hilbert Action.
	Abstract	In this talk, I will give a review of the basics of General Relativity for those who wish to brush up on the main points. Included will be a brief overview of the mathematical formalism and geometrical description of GR, with a quick reminder of how the Newtonian results were generalized in this context. I will also go over GR as a classical field theory, and how the Einstein Equations may be derived from a suitable Action.
	References	"An Introduction to General Relativity: Spacetime and Geometry." Sean M. Caroll "General Relativity." R. Wald (1984) "Geometrical Methods of Mathematical Physics." B. Schutz

SUMMER 2009

AUGUST 18
	Speaker	Qiaoli Yang
	Title	Axions and Dark Matter
	Abstract	Axions are one of the candidates for solving the dark matter puzzle. While current lab experiments still cannot find evidence of its existence, the formation of Axion-BEC (Bose Einstein Condesate) in the universe may provide us new possibilities.
	References	P.Sikivie - "Axions" P.Sikivie, Q. Yang - "Bose-Einstein Condensation of Dark Matter Axions" hep-ph/0901.1106

AUGUST 4
	Speaker	Tongguang Cheng
	Title	Anomalies
	Abstract	An Anomaly is the failure of a classical symmetry. Noether's theorem states that to every global continuous symmetry of the action, one can associate a current that is classically conserved. However, a classical symmetry may be "softly" broken at the quantum level. An Anomaly is precisely this kind of breaking of a classical symmetry. I'm going to use the chiral anomaly as an example to show where anomalies come from and how to compute them. If there is still enough time, I will talk a little bit about the trace anomaly in conformal field theory.
	References	Ramond P. - Field Theory A Modern Primer 2D Edition, Chapter 8

JULY 28
	Speaker	Chris Pankow
	Title	Why the graviton is a spin 2 particle and gravitational waves
	Note	Room change for today: -> Rm 2260
	Abstract	Gravitational waves are the last remaining undiscovered confirmation of general relativity as a theory of gravitation. They are also used as a fundamental building block of the extensions of quantum field theory into the regime of gravity. In their quantized version, they are considered particles known as gravitons, a spin two tensor field. In this talk, I will discuss the development of gravitational waves from the Einstein equations, and then show some of the connections between the classical picture of gravitational waves and the graviton as a field theory. Finally, I will discuss the reasons that the graviton must be a spin two field from a semi-classical standpoint. The discussion will follow and borrow heavily from Gravitational Waves, Vol 1, by Michele Maggiore.
	References	M. Maggiore "Gravitational Waves" Chapters 1 and 2

JULY 21
	Speaker	Ali Ashrafi
	Title	Taming Nonrenormalizability
	Abstract	"The goal of a proper renormalization scheme for perturbatively nonrenormalizable scalar quantum field theories should be to neutralize the source of the divergences. Achieving this goal requires an entirely different kind of counterterm than those typically employed, and including the appropriate counterterm as part of a pseudofree model about which to expand leads to an alternative perturbative formulation that is term-by-term finite."
	References	J.R. Klauder, "Beyond Conventional Quantization", (Cambridge University Press, Cambridge, 2000 & 2005) J.R. Klauder, "A New Approach to Nonrenormalizable Models", Ann. Phys. 322, 2569-2602 (2007). J.R. Klauder, “Taming Nonrenormalizability”, arXiv:0811.3386

JULY 14
	Speaker	All participants
	Title	Roundtable Discussion NOTE : Time 4:30 in IFT Reading Room (Rm 2175)
	Abstract	The idea is that we sit down and discuss about any topic, exchange questions, problems, knowledge or anything you feel like discussing about HET/Pheno.
	References	NA

JULY 7
	Speaker	All participants
	Title	Roundtable Discussion NOTE : Time 4:30 in IFT Reading Room (Rm 2175)
	Abstract	The idea is that we sit down and discuss about any topic, exchange questions, problems, knowledge or anything you feel like discussing about HET/Pheno.
	References	NA

JUNE 30
	Speaker	Patrick Hearin
	Title	Yang-Mills Field Theories in the Light-Cone Gauge
	Abstract	Light-Cone formalism has recently become a useful tool for investigating supersymmetric field theories. The non-physical degrees of freedom are canceled by applying a gauge and the equations of motion. This produces a tedious expansion in the physical fields breaking the covariance. First we will review Yang-Mills Field Theory for a vector particle in a covariant and light-cone gauge. Then we derive the Beta Function for both gauges.
	References	Pierre Ramond, Field Theory: A Modern Primer, Chapters: 7-8 Michael E. Peskin, Dan V. Schroeder, An Introduction to Quantum Field Theory, chapters: 15-16 Barton Zwiebach, A First Course In String Theory, Chapters: 1,2,3,10,11 Avaroth Harindranath, An Introduction to Light-Front Dynamics for Pedestrians, arXiv:hep-ph/9612244v2

JUNE 23
	Speaker	Francisco Rojas
	Title	Renormalization (Part 2)
	Abstract	Here we will continue last week's talk. We will also discuss non-renormalizable theories very briefly and regularization techniques.
	References	M.Srednicki, Quantum Field Theory. Chapters: 17,18. P. Ramond, Field Theory A Modern Primer (Second Edition). Chapters:4 and 8.8 A. Zee, Quantum Field Theory in a Nutshell. Part III

JUNE 16
	Speaker	Francisco Rojas
	Title	Renormalization (Part 1)
	Abstract	In this talk we will review the basics of renormalization such as the modern interpretation of a renormalizable theory (lagrangian), criteria to recognize renormalizability, renormalization schemes and renormalization group equations.
	References	M.Srednicki, Quantum Field Theory. Chapters: 17,18. P. Ramond Field Theory A Modern Primer (Second Edition). Chapters:4 and 8.8 A. Zee, Quantum Field Theory in a Nutshell. Part III