DOCSLIB.ORG

Exciting an Avalanche Mohammad Maghrebi and Colleagues Have Nature Photon

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Exciting an Avalanche Mohammad Maghrebi and Colleagues Have Nature Photon research highlights Shrink from tension closely related to networks characterized by be created from nothing. Hawking radiation Nature Mater. 11, 608–613 (2012) suboptimal equilibria that can be optimized via and the dynamical Casimir effect are structural constraints — like a traffic network examples of the macroscopic manifestation that profits from the removal of a road. In the of quantum vacuum fluctuations — near case of the proposed metamaterials, however, black-hole event horizons or accelerating the optimization occurs spontaneously, in boundaries, photons pop out of the vacuum. response to a change in applied force. AK Such spontaneous emission is also expected to occur in the presence of spinning bodies: Exciting an avalanche Mohammad Maghrebi and colleagues have Nature Photon. 6, 455–458 (2012) uncovered a new twist. Spontaneous emission from rotating An individual electron does not have a large objects was predicted in the 1970s, but influence on the world around it, which Maghrebi et al. have revisited the theory makes detection tricky. One successful and introduced an exact theoretical approach is to use avalanche amplification: treatment of vacuum fluctuations in one seed electron generates two ‘daughter’ the presence of a spinning body. Their electrons; this is repeated to create four, scattering-theory approach not only © JUPITERIMAGES/GETTY IMAGES/THINKSTOCK © JUPITERIMAGES/GETTY and so on, until a measurable current is confirms that energy is emitted by the produced. Gabriele Bulgarini and colleagues spinning object even at zero temperature, Squeezing a material between your fingers have now applied this idea to the charge but also signals a previously unknown ordinarily results in compression. Imagine carriers trapped in single quantum dots. effect: the radiation from a rotating body then, if that same material were to expand Excitons — an electron and its positively exerts pressure on a nearby test object, in response to your touch. Counterintuitive charged counterpart, a hole — in a quantum which is dragged along and starts rotating though it may seem, Zachary Nicolaou and dot are one candidate for quantum bits. parallel to the rotation axis. A similar Adilson Motter have uncovered a design However, studies on single quantum dots effect is expected for the generalization to principle for metamaterials that exhibit often require that a measurement is repeated relativistic motion. IG such negative compressibility — expanding thousands of times: not ideal in a superfast with applied pressure and contracting quantum computer. Opposites form Cooper pairs under tension. Bulgarini et al. integrated their quantum Phys Rev. B. 85, 195206 (2012) Experience tells us such materials dot into a nanowire avalanche photodetector. shouldn’t exist, but that scepticism is also A photon generates a single exciton in the dot. In a superconductor, current is carried firmly grounded in thermodynamics: for The electron and hole tunnel out of the dot by bound pairs of like charges. For these a closed system in equilibrium, negative in opposite directions into a multiplication ‘Cooper pairs’ to form there must be some compressibility represents an unstable region, thus generating a useful photocurrent. mechanism to oppose their Coulombic configuration. This argument holds when The team show that 120 individual excitation repulsion: in conventional superconductors, the applied force increases infinitesimally, so events were required for electrical read-out of it’s mediated by phonons. Under certain that stability does not change as the force is the exciton — 10,000 times fewer than other conditions, however, Cooper pairs of varied. In reality, however, changes in applied approaches and a significant step towards the unlike charges — an electron and a force can be appreciable, changing stability ultimate goal of single-shot read-out. DG hole — might also form, provided their and causing the system to shift to a different Coulomb attraction is counteracted to stable configuration. Out of the vacuum impede recombination. Nicolaou and Motter exploit this concept Phys. Rev. Lett. 108, 230403 (2012) Marijn Versteegh and colleagues report to design materials for which the switch to evidence that electron–hole Cooper-pair a new configuration induces an expansion A surprising consequence of Heisenberg’s formation could occur in a photoexcited on application of pressure. The idea is uncertainty principle is that something can electron–hole gas in a semiconductor. At low density, Coulomb attraction binds electron–hole pairs tightly. But as the density Branching out Phys. Rev. Lett. 108, 231801 (2012) is increased, this attraction is screened and becomes gradually weaker. And at high According to the standard model of particle physics, flavour-changing neutral currents — densities it could become weak enough to interactions that can change the flavour of a particle but without changing its charge — are be balanced by Pauli repulsion, enabling suppressed. This physics emerged in the late 1960s from the study of K0 mesons, which Cooper pairs to form. didn’t seem to decay to pairs of muons as expected (and links to the postulation and Versteegh et al. subjected a ZnO subsequent discovery in 1974 of the charm quark). The effect is even more pronounced crystal to an intense infrared laser light. in heavier B0 mesons, and so the LHCb collaboration (R. Aaji et al.) has searched its data As they increased the laser intensity and for evidence of these particles decaying to pairs of muons: any measurable effect would decreased the temperature, they observed indicate some physics not yet included in the standard model. the emergence of a peak in the resulting LHCb finds none, and has instead set limits on the ‘branching fractions’ (a measure of the emission spectra consistent with the 0 probability of the decay) into a muon pair of two types of B meson — the Bs (a bound bottom recombination of preformed electron–hole and strange quark) and the B0 (a bound bottom and down quark). The limits are the tightest yet, Cooper pairs. EG constraining the branching fractions to be less than a few parts in a billion — and coming in close now to the tiny, almost negligible, branching fractions predicted in the standard model. AW Written by Iulia Georgescu, Ed Gerstner, David Gevaux, Abigail Klopper and Alison Wright 510 NATURE PHYSICS | VOL 8 | JULY 2012 | www.nature.com/naturephysics © 2012 Macmillan Publishers Limited. All rights reserved.
Load more

Recommended publications
  • Quantum Field Theory*
    Quantum Field Theory y Frank Wilczek Institute for Advanced Study, School of Natural Science, Olden Lane, Princeton, NJ 08540 I discuss the general principles underlying quantum eld theory, and attempt to identify its most profound consequences. The deep est of these consequences result from the in nite number of degrees of freedom invoked to implement lo cality.Imention a few of its most striking successes, b oth achieved and prosp ective. Possible limitation s of quantum eld theory are viewed in the light of its history. I. SURVEY Quantum eld theory is the framework in which the regnant theories of the electroweak and strong interactions, which together form the Standard Mo del, are formulated. Quantum electro dynamics (QED), b esides providing a com- plete foundation for atomic physics and chemistry, has supp orted calculations of physical quantities with unparalleled precision. The exp erimentally measured value of the magnetic dip ole moment of the muon, 11 (g 2) = 233 184 600 (1680) 10 ; (1) exp: for example, should b e compared with the theoretical prediction 11 (g 2) = 233 183 478 (308) 10 : (2) theor: In quantum chromo dynamics (QCD) we cannot, for the forseeable future, aspire to to comparable accuracy.Yet QCD provides di erent, and at least equally impressive, evidence for the validity of the basic principles of quantum eld theory. Indeed, b ecause in QCD the interactions are stronger, QCD manifests a wider variety of phenomena characteristic of quantum eld theory. These include esp ecially running of the e ective coupling with distance or energy scale and the phenomenon of con nement.
    [Show full text]
  • Baryon and Lepton Number Anomalies in the Standard Model
    Appendix A Baryon and Lepton Number Anomalies in the Standard Model A.1 Baryon Number Anomalies The introduction of a gauged baryon number leads to the inclusion of quantum anomalies in the theory, refer to Fig. 1.2. The anomalies, for the baryonic current, are given by the following, 2 For SU(3) U(1)B , ⎛ ⎞ 3 A (SU(3)2U(1) ) = Tr[λaλb B]=3 × ⎝ B − B ⎠ = 0. (A.1) 1 B 2 i i lef t right 2 For SU(2) U(1)B , 3 × 3 3 A (SU(2)2U(1) ) = Tr[τ aτ b B]= B = . (A.2) 2 B 2 Q 2 ( )2 ( ) For U 1 Y U 1 B , 3 A (U(1)2 U(1) ) = Tr[YYB]=3 × 3(2Y 2 B − Y 2 B − Y 2 B ) =− . (A.3) 3 Y B Q Q u u d d 2 ( )2 ( ) For U 1 BU 1 Y , A ( ( )2 ( ) ) = [ ]= × ( 2 − 2 − 2 ) = . 4 U 1 BU 1 Y Tr BBY 3 3 2BQYQ Bu Yu Bd Yd 0 (A.4) ( )3 For U 1 B , A ( ( )3 ) = [ ]= × ( 3 − 3 − 3) = . 5 U 1 B Tr BBB 3 3 2BQ Bu Bd 0 (A.5) © Springer International Publishing AG, part of Springer Nature 2018 133 N. D. Barrie, Cosmological Implications of Quantum Anomalies, Springer Theses, https://doi.org/10.1007/978-3-319-94715-0 134 Appendix A: Baryon and Lepton Number Anomalies in the Standard Model 2 Fig. A.1 1-Loop corrections to a SU(2) U(1)B , where the loop contains only left-handed quarks, ( )2 ( ) and b U 1 Y U 1 B where the loop contains only quarks For U(1)B , A6(U(1)B ) = Tr[B]=3 × 3(2BQ − Bu − Bd ) = 0, (A.6) where the factor of 3 × 3 is a result of there being three generations of quarks and three colours for each quark.
    [Show full text]
  • Introduction to Supersymmetry
    Introduction to Supersymmetry Pre-SUSY Summer School Corpus Christi, Texas May 15-18, 2019 Stephen P. Martin Northern Illinois University [email protected] 1 Topics: Why: Motivation for supersymmetry (SUSY) • What: SUSY Lagrangians, SUSY breaking and the Minimal • Supersymmetric Standard Model, superpartner decays Who: Sorry, not covered. • For some more details and a slightly better attempt at proper referencing: A supersymmetry primer, hep-ph/9709356, version 7, January 2016 • TASI 2011 lectures notes: two-component fermion notation and • supersymmetry, arXiv:1205.4076. If you find corrections, please do let me know! 2 Lecture 1: Motivation and Introduction to Supersymmetry Motivation: The Hierarchy Problem • Supermultiplets • Particle content of the Minimal Supersymmetric Standard Model • (MSSM) Need for “soft” breaking of supersymmetry • The Wess-Zumino Model • 3 People have cited many reasons why extensions of the Standard Model might involve supersymmetry (SUSY). Some of them are: A possible cold dark matter particle • A light Higgs boson, M = 125 GeV • h Unification of gauge couplings • Mathematical elegance, beauty • ⋆ “What does that even mean? No such thing!” – Some modern pundits ⋆ “We beg to differ.” – Einstein, Dirac, . However, for me, the single compelling reason is: The Hierarchy Problem • 4 An analogy: Coulomb self-energy correction to the electron’s mass A point-like electron would have an infinite classical electrostatic energy. Instead, suppose the electron is a solid sphere of uniform charge density and radius R. An undergraduate problem gives: 3e2 ∆ECoulomb = 20πǫ0R 2 Interpreting this as a correction ∆me = ∆ECoulomb/c to the electron mass: 15 0.86 10− meters m = m + (1 MeV/c2) × .
    [Show full text]
  • The Standard Model and Beyond Maxim Perelstein, LEPP/Cornell U
    The Standard Model and Beyond Maxim Perelstein, LEPP/Cornell U. NYSS APS/AAPT Conference, April 19, 2008 The basic question of particle physics: What is the world made of? What is the smallest indivisible building block of matter? Is there such a thing? In the 20th century, we made tremendous progress in observing smaller and smaller objects Today’s accelerators allow us to study matter on length scales as short as 10^(-18) m The world’s largest particle accelerator/collider: the Tevatron (located at Fermilab in suburban Chicago) 4 miles long, accelerates protons and antiprotons to 99.9999% of speed of light and collides them head-on, 2 The CDF million collisions/sec. detector The control room Particle Collider is a Giant Microscope! • Optics: diffraction limit, ∆min ≈ λ • Quantum mechanics: particles waves, λ ≈ h¯/p • Higher energies shorter distances: ∆ ∼ 10−13 cm M c2 ∼ 1 GeV • Nucleus: proton mass p • Colliders today: E ∼ 100 GeV ∆ ∼ 10−16 cm • Colliders in near future: E ∼ 1000 GeV ∼ 1 TeV ∆ ∼ 10−17 cm Particle Colliders Can Create New Particles! • All naturally occuring matter consists of particles of just a few types: protons, neutrons, electrons, photons, neutrinos • Most other known particles are highly unstable (lifetimes << 1 sec) do not occur naturally In Special Relativity, energy and momentum are conserved, • 2 but mass is not: energy-mass transfer is possible! E = mc • So, a collision of 2 protons moving relativistically can result in production of particles that are much heavier than the protons, “made out of” their kinetic
    [Show full text]
  • 6 STANDARD MODEL: One-Loop Structure
    6 STANDARD MODEL: One-Loop Structure Although the fundamental laws of Nature obey quantum mechanics, mi- croscopically challenged physicists build and use quantum field theories by starting from a classical Lagrangian. The classical approximation, which de- scribes macroscopic objects from physics professors to dinosaurs, has in itself a physical reality, but since it emerges only at later times of cosmological evolution, it is not fundamental. We should therefore not be too surprised if unforeseen special problems and opportunities emerge in the analysis of quantum perturbations away from the classical Lagrangian. The classical Lagrangian is used as input to the path integral, whose eval- uation produces another Lagrangian, the effective Lagrangian, Leff , which encodes all the consequences of the quantum field theory. It contains an infinite series of polynomials in the fields associated with its degrees of free- dom, and their derivatives. The classical Lagrangian is reproduced by this expansion in the lowest power of ~ and of momentum. With the notable exceptions of scale invariance, and of some (anomalous) chiral symmetries, we think that the symmetries of the classical Lagrangian survive the quanti- zation process. Consequently, not all possible polynomials in the fields and their derivatives appear in Leff , only those which respect the symmetries. The terms which are of higher order in ~ yield the quantum corrections to the theory. They are calculated according to a specific, but perilous path, which uses the classical Lagrangian as input. This procedure gener- ates infinities, due to quantum effects at short distances. Fortunately, most fundamental interactions are described by theories where these infinities can be absorbed in a redefinition of the input parameters and fields, i.e.
    [Show full text]
  • On the Metastability of the Standard Model Vacuum
    CERN–TH/2001–092 LNF-01/014(P) GeF/TH/6-01 IFUP–TH/2001–11 hep-ph/0104016 On the metastability of the Standard Model vacuum Gino Isidori1, Giovanni Ridolfi2 and Alessandro Strumia3 Theory Division, CERN, CH-1211 Geneva 23, Switzerland Abstract If the Higgs mass mH is as low as suggested by present experimental information, the Standard Model ground state might not be absolutely stable. We present a detailed analysis of the lower bounds on mH imposed by the requirement that the electroweak vacuum be sufficiently long-lived. We perform a complete one-loop calculation of the tunnelling probability at zero temperature, and we improve it by means of two-loop renormalization-group equations. We find that, for mH = 115 GeV, the Higgs potential develops an instability below the Planck scale for mt > (166 2) GeV, but the electroweak ± vacuum is sufficiently long-lived for mt < (175 2) GeV. ± 1On leave from INFN, Laboratori Nazionali di Frascati, Via Enrico Fermi 40, I-00044 Frascati, Italy. 2On leave from INFN, Sezione di Genova, Via Dodecaneso 33, I-16146 Genova, Italy. 3On leave from Dipartimento di Fisica, Universit`a di Pisa and INFN, Sezione di Pisa, Italy. 1 Introduction If the Higgs boson if sufficiently lighter than the top quark, radiative corrections induced by top loops destabilize the electroweak minimum and the Higgs potential of the Standard Model (SM) becomes unbounded from below at large field values. The requirement that such an unpleasant scenario be avoided, at least up to some scale Λ characteristic of some kind of new physics [1, 2], leads to a lower bound on the Higgs mass mH that depends on the value of the top quark mass mt, and on Λ itself.
    [Show full text]
  • Standard Model & Baryogenesis at 50 Years
    Standard Model & Baryogenesis at 50 Years Rocky Kolb The University of Chicago The Standard Model and Baryogenesis at 50 Years 1967 For the universe to evolve from B = 0 to B ¹ 0, requires: 1. Baryon number violation 2. C and CP violation 3. Departure from thermal equilibrium The Standard Model and Baryogenesis at 50 Years 95% of the Mass/Energy of the Universe is Mysterious The Standard Model and Baryogenesis at 50 Years 95% of the Mass/Energy of the Universe is Mysterious Baryon Asymmetry Baryon Asymmetry Baryon Asymmetry The Standard Model and Baryogenesis at 50 Years 99.825% of the Mass/Energy of the Universe is Mysterious The Standard Model and Baryogenesis at 50 Years Ω 2 = 0.02230 ± 0.00014 CMB (Planck 2015): B h Increasing baryon component in baryon-photon fluid: • Reduces sound speed. −1 c 3 ρ c =+1 B S ρ 3 4 γ • Decreases size of sound horizon. η rdc()η = ηη′′ ( ) SS0 • Peaks moves to smaller angular scales (larger k, larger l). = π knrPEAKS S • Baryon loading increases compression peaks, lowers rarefaction peaks. Wayne Hu The Standard Model and Baryogenesis at 50 Years 0.021 ≤ Ω 2 ≤0.024 BBN (PDG 2016): B h Increasing baryon component in baryon-photon fluid: • Increases baryon-to-photon ratio η. • In NSE abundance of species proportional to η A−1. • D, 3He, 3H build up slightly earlier leading to more 4He. • Amount of D, 3He, 3H left unburnt decreases. Discrepancy is fake news The Standard Model and Baryogenesis at 50 Years = (0.861 ± 0.005) × 10 −10 Baryon Asymmetry: nB/s • Why is there an asymmetry between matter and antimatter? o Initial (anthropic?) conditions: .
    [Show full text]
  • Standard Model of Particle Physics, Or Beyond?
    Standard Model of Particle Physics, or Beyond? Mariano Quir´os High Energy Phys. Inst., BCN (Spain) ICTP-SAIFR, November 13th, 2019 Outline The outline of this colloquium is I Standard Model: reminder I Electroweak interactions I Strong interactions I The Higgs sector I Experimental successes I Theoretical and observational drawbacks I Beyond the Standard Model I Supersymmetry I Large extra dimensions I Warped extra dimensions/composite Higgs I Concluding remarks Disclaimer: I will not discuss any technical details. With my apologies to my theorist (and experimental) colleagues The Standard Model: reminder I The knowledge of the Standard Model of strong and electroweak interactions requires (as any other physical theory) the knowledge of I The elementary particles or fields (the characters of the play) I How particles interact (their behavior) The characters of the play I Quarks: spin-1/2 fermions I Leptons: spin-1/2 fermions I Higgs boson: spin-0 boson I Carriers of the interactions: spin-1 (gauge) bosons I All these particles have already been discovered and their mass, spin, and charge measured \More in detail the characters of the play" - Everybody knows the Periodic Table of the Elements - Compare elementary particles with some (of course composite) very heavy nuclei What are the interactions between the elementary building blocks of the Standard Model? I Interactions are governed by a symmetry principle I The more symmetric the theory the more couplings are related (the less of them they are) and the more predictive it is Strong interactions:
    [Show full text]
  • Introduction to the Standard Model New Horizons in Lattice Field Theory IIP Natal, March 2013
    Introduction to the Standard Model New Horizons in Lattice Field Theory IIP Natal, March 2013 Rogerio Rosenfeld IFT-UNESP Lecture 1: Motivation/QFT/Gauge Symmetries/QED/QCD Lecture 2: QCD tests/Electroweak Sector/Symmetry Breaking Lecture 3: Sucesses/Shortcomings of the Standard Model Lecture 4: Beyond the Standard Model New Horizons in Lattice QCD 1 • Quigg: Gauge Theories of Strong, Weak, and Electromagnetic Interactions • Halzen and Martin: Quarks and Leptons • Peskin and Schroeder: An Introduction to Quantum Field Theory • Donoghue, Golowich and Holstein: Dynamics of the Standard Model • Barger and Phillips: Collider Physics • Rosenfeld: http://www.sbfisica.org.br/~evjaspc/xvi/ • Hollik: arXiv:1012.3883 • Buchmuller and Ludeling: arXiv:hep-ph/0609174 • Rosner’s Resource Letter: arXiv:hep-ph/0206176 • Quigg: arXiv:0905.3187 • Altarelli: arXiv:1303.2842 New Horizons in Lattice QCD 2 New Horizons in Lattice QCD 3 • 1906: Electron (J. J. Thomson, 1897) • 33: QED (Dirac) • 36: Positron (Anderson, 1932) • 57: Parity violation (Lee and Yang, 56) • 65: QED (Feynman, Schwinger and Tomonaga) • 69: Eightfold way (Gell-Mann, 63) • 74: Charm (Richter and Ting, 74) • 79: SM (Glashow, Weinberg and Salam, 67-68) • 80: CP violation (Cronin and Fitch, 64) • 84: W&Z (Rubbia and Van der Meer, 83) • 88: b quark (Lederman, Schwartz and Steinberger, 77) • 90: Quarks (Friedman, Kendall and Taylor, 67-73) • 95: Neutrinos (Reines, 56); Tau (Perl, 77) • 99: Renormalization (Veltman and ‘t Hooft, 71) • 02: Neutrinos from the sky (Davis and Koshiba) • 04: Asymptotic freedom (Gross, Politzer and Wilczek) • 08: CP violation (KM) and SSB (Nambu) New Horizons in Lattice QCD 4 The Nobel Prize in Physics 2008 Y.
    [Show full text]
  • The Quantum Vacuum and the Cosmological Constant Problem
    The Quantum Vacuum and the Cosmological Constant Problem S.E. Rugh∗and H. Zinkernagely To appear in Studies in History and Philosophy of Modern Physics Abstract - The cosmological constant problem arises at the intersection be- tween general relativity and quantum field theory, and is regarded as a fun- damental problem in modern physics. In this paper we describe the historical and conceptual origin of the cosmological constant problem which is intimately connected to the vacuum concept in quantum field theory. We critically dis- cuss how the problem rests on the notion of physically real vacuum energy, and which relations between general relativity and quantum field theory are assumed in order to make the problem well-defined. 1. Introduction Is empty space really empty? In the quantum field theories (QFT’s) which underlie modern particle physics, the notion of empty space has been replaced with that of a vacuum state, defined to be the ground (lowest energy density) state of a collection of quantum fields. A peculiar and truly quantum mechanical feature of the quantum fields is that they exhibit zero-point fluctuations everywhere in space, even in regions which are otherwise ‘empty’ (i.e. devoid of matter and radiation). These zero-point fluctuations of the quantum fields, as well as other ‘vacuum phenomena’ of quantum field theory, give rise to an enormous vacuum energy density ρvac. As we shall see, this vacuum energy density is believed to act as a contribution to the cosmological constant Λ appearing in Einstein’s field equations from 1917, 1 8πG R g R Λg = T (1) µν − 2 µν − µν c4 µν where Rµν and R refer to the curvature of spacetime, gµν is the metric, Tµν the energy-momentum tensor, G the gravitational constant, and c the speed of light.
    [Show full text]
  • The Elusive Gluon
    CAFPE-185/14 CERN-PH-TH-2014-216 DESY 14-213 SISSA 60/2014/FISI UG-FT-315/14 The Elusive Gluon Mikael Chala1,2, José Juknevich3,4, Gilad Perez5 and José Santiago1,6 1CAFPE and Departamento de Física Teórica y del Cosmos, Universidad de Granada, E-18071 Granada, Spain 2 DESY, Notkestrasse 85, 22607 Hamburg, Germany 3SISSA/ISAS, I-34136 Trieste, Italy 4INFN - Sezione di Trieste, 34151 Trieste, Italy 5Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel 6CERN, Theory Division, CH1211 Geneva 23, Switzerland Abstract We study the phenomenology of vector resonances in the context of natural com- posite Higgs models. A mild hierarchy between the fermionic partners and the vector resonances can be expected in these models based on the following arguments. Both di- rect and indirect (electroweak and flavor precision) constraints on fermionic partners are milder than the ones on spin one resonances. Also the naturalness pressure coming from the top partners is stronger than that induced by the gauge partners. This observation implies that the search strategy for vector resonances at the LHC needs to be modified. In particular, we point out the importance of heavy gluon decays (or other vector res- onances) to top partner pairs that were overlooked in previous experimental searches at the LHC. These searches focused on simplified benchmark models in which the only new particle beyond the Standard Model was the heavy gluon. It turns out that, when kinematically allowed, such heavy-heavy decays make the heavy gluon elusive, and the bounds on its mass can be up to 2 TeV milder than in the simpler models considered so arXiv:1411.1771v2 [hep-ph] 9 Jan 2015 far for the LHC14.
    [Show full text]
  • Beyond the Standard Model: Supersymmetry
    Beyond the Standard Model: supersymmetry I. Antoniadis1 and P. Tziveloglou2 CERN, Geneva, Switzerland Abstract In these lectures we cover the motivations, the problem of mass hierarchy, and the main proposals for physics beyond the Standard Model; supersymme- try, supersymmetry breaking, soft terms; Minimal Supersymmetric Standard Model; grand unification; and strings and extra dimensions. 1 Departure from the Standard Model 1.1 Why beyond the Standard Model? Almost all research in theoretical high energy physics of the last thirty years has been concentrated on the quest for the theory that will replace the Standard Model (SM) as the proper description of nature at the energies beyond the TeV scale. Thus it is important to know if this quest is justified or not, given that the SM is a very successful theory that has offered to us some of the most striking agreements between experimental data and theoretical predictions. We shall start by briefly examining the reasons for leaving behind such a successful SM. Actually there is a variety of such arguments, both theoretical and experimental, that lead to the undoubtable conclusion that the Standard Model should be only an effective theory of a more fundamental one. We briefly mention some of the most important arguments. Firstly, the Standard Model does not include gravity. It says absolutely nothing about one of the four fundamental forces of nature. Another is the popular ‘mass hierarchy’ problem. Within the SM, the mass of the higgs particle is extremely sensitive to any new physics at higher energies and its natural value is of order of the Planck mass, if the SM is valid up to that scale.
    [Show full text]