1 / 18

String Theory: An Introduction

String Theory: An Introduction. Paramita Barai Physics 8610 Course Project Presentation. Contents. Why Strings ? String Theory – Basics, New Ideas & Concepts String Interactions & Particles Successful Predictions of String Theory In Cosmology

azucena
Download Presentation

String Theory: An Introduction

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. String Theory: An Introduction Paramita Barai Physics 8610 Course Project Presentation

  2. Contents • Why Strings ? • String Theory – Basics, New Ideas & Concepts • String Interactions & Particles • Successful Predictions of String Theory • In Cosmology • As the Theory of Everything (Grand Unification) • Experimental tests • People & Groups • Conclusions P. Barai

  3. Several discrepancies in existing theories to explain the nature completely Particle Physics No connection between fermions & bosons by any existing theory Calculations lead to infinite quantities (Singular behavior) in several cases: at very short distances (Planck Scale). Cosmology Big Bang & Black Hole Singularity unexplained All theories break down (can’t be applied meaningfully) Relativity, Quantum Field Theory  Infinite answers Grand Unification Can’t unify Relativity with Quantum Mechanics: no massless, spin–2 particle (graviton) in Quantum Mechanics Why String Theory ? P. Barai

  4. Everything in the universe – oscillations of tiny, vibrating STRINGS Characteristic size / Minimum observable length for Quantum String Theory, LString ~ Planck length, LPlanck (Lowest distance probed ~ 10–16 cm) String tension, TString Open String Standard particles Closed String  Gravitons From different Boundary Conditions String Theory: Basics P. Barai

  5. Revolutionary ideas • Requires 10 dimensions • 10 = 3 (Space: x, y, z) + 1 (Time: t) + 6 (Where are they ?) • Extra dimensions • Small compact space (of size Lst) attached to each point in ordinary 4D space-time: Compactification • Large – Brane-world hypothesis - We are trapped on the surface of a higher dimensional brane • Branes: Membrane–like objects • You can think of a brane as being a slice through the higher dimensional world that string theory says exists • Particles that we're made out of and the forces that hold us together might actually be living on one of these branes P. Barai

  6. Brief timeline • 1921: Kaluza–Klein theory: (4D space) • 1970: Birth of String Theory – by Yoichiro Nambu, Leonard Susskind, Holger Nielsen – (To describe the strong force) • 1971: Supersymmetry (SUSY) • 1974: String Theory predicts Gravitons: Unification • 1980: Superstrings: Supersymmetry + Strings (Michael Green & John Schwarz) • 1984: First Revolution: Quantum anomalies cancel • 1991-95: Second Revolution, Duality, M Theory (Edward Witten & Townsend) • 1996: Black Hole entropy accounted for (Andy Strominger & Cumrun Vafa) P. Barai

  7. Strings  Particles • String vibrates – Sweeps out a 2–dimensional surface in space-time: ‘world sheet’ (compared to 1D ‘world line’ of a particle) • Quantum modes of vibration of strings  Particles in Spacetime • String vibrational modes characterized by various quantum numbers: mass, spin, etc. • Each mode carries a set of quantum numbers that correspond to a distinct type of fundamental particle. • The quantized string oscillator modes wind up giving representations of the Poincaré group, through which quantum states of mass and spin are classified in a relativistic quantum field theory. • Characteristics of particles: • Distance – momentum relation • Mass – Spin relation P. Barai

  8. Particle physics interactions At a point Zero distance in Feynman diagram Loop Integrals – Infinite String interactions Not at a point; but spread out. More sensible quantum behavior. Feynman diagram in Standard Model  2–D smooth surface in String Theory Loop Integrals – Finite Strings interact in ways that correspond to the observed interactions of particles. P. Barai

  9. Successful Predictions • The right types of particles and the right types of interactions among them. • At low energies the interactions are precisely of the type appearing in the Standard Model. • Explains gravitation (via massless spin–2 particle -- graviton -- the quantum of gravitation), approximated at low energies by general relativity. (No other quantum theory has this) • Supersymmetry (SUSY) at low energies (the electroweak scale): Fermions  Bosons • Successful predictions in Cosmology & Grand Unification P. Barai

  10. Cosmology: the present universe • Constituents of the Universe • Matter: • Galaxies • Other structures • Dark matter • Radiation • Vacuum ( ? ) • History of Universe from Big Bang till today .. • Universe is Flat & Isotropic in large scale • Inflation P. Barai

  11. P. Barai

  12. Stringy Solution to Big Bang • String Theory changes the nature of the Big Bang. • Universe starts in less singular way • Stringy minimum distance phenomenon  turns the initial infinite behavior into something that's finite • By String Theory : • Everything crunched down to a very small size, but not infinitely small. • Temperature very large, but not infinitely big. • Big bounce: before Big Bang, there was an universe that was bigger  contraction  quantum mechanical intermediate stage Big Bang & our present Universe • Big Bang by Collisions of branes • Branes in String Theory helps to explain Inflation P. Barai

  13. The Grand Unified Theory:The Holy Grail of Physics • Should unify all forces • Complete description of quantum dynamics • All other physical constants like = 1/137; Mproton/Melectron; e … are pure numbers and they should be calculable in this theory. • Contain very less number of input parameters • Should provide initial conditions, (to explain why we are in the particular universe we do) • Only serious candidate – String Theory. • Unified Quantum Mechanics with Gravity P. Barai

  14. Advantages of Strings in Unification • Superstring theory overcomes the problem of singularity at short distances • Point–like particles  one-dimensional extended strings • Introduces fuzziness, which captures the reality • Superstring theory: • Modifies General Relativity. • Difficult to integrate Relativity to Quantum Field Theory by perturbation • Recent discoveries  non-perturbative solns. P. Barai

  15. Can String theory be the probable Grand Unified Theory ? • Unifies in a single 4 – dimensional quantum theory all known forces and elementary particles • Reduces the number of parameters (that need to be determined by experiments) • 20 & 30 (assuming massive neutrinos)  1 (String Tension) + Planck's constant + velocity of light P. Barai

  16. Detect extra dimension. Energy can leak from our known 4 dimensions to the extra compactified dimensions in appropriate conditions  Missing Energy in accelerators Detect s partner of some particle (prediction of SUSY) s particles much more massive So cant be generated by present accelerators Big string produced at exotic conditions of Big Bang – Observe by telescopes. Possible experimental tests P. Barai

  17. Princeton (Witten, David Gross) Caltech (Schwarz) Columbia University (Brian Green) Cambridge Cornell UCSB CERN Accelerator LHC – will begin operating in Geneva, Switzerland ~ 2007; its energy will be about 8000 GeV per beam Fermilab Search for missing energy People and Groups P. Barai

  18. ‘String Theory is the science of 21st century accidentally discovered in 20th century’ … Wait for what future gives … THANK YOU ALL Conclusions P. Barai

More Related