Particle Physics

We review the holographic correspondence between field theories and string/M theory, focusing on the relation between compactifications of string/M theory on Anti-de Sitter spaces and conformal field theories. We review the background for this correspondence and discuss its motivations and the evidence for its correctness. We describe the main results that have been derived from the correspondence in the regime that the field theory is approximated by classical or semiclassical gravity. We focus on the case of the N = 4 supersymmetric gauge theory in four dimensions, but we discuss also field theories in other dimensions, conformal and non-conformal, with or without supersymmetry, and in particular the relation to QCD. We also discuss some implications for black hole physics.

In this paper we review in detail a number of approaches that have been adopted to try and explain the remarkable observation of our accelerating Universe. In particular we discuss the arguments for and recent progress made towards understanding the nature of dark energy. We review the observational evidence for the current accelerated expansion of the universe and present a number of dark energy models in addition to the conventional cosmological constant, paying particular attention to scalar field models such as quintessence, K-essence, tachyon, phantom and dilatonic models. The importance of cosmological scaling solutions is emphasized when studying the dynamical system of scalar fields including coupled dark energy. We study the evolution of cosmological perturbations allowing us to confront them with the observation of the Cosmic Microwave Background and Large Scale Structure and demonstrate how it is possible in principle to reconstruct the equation of state of dark energy by also using Supernovae Ia observational data. We also discuss in detail the nature of tracking solutions in cosmology, particle physics and braneworld models of dark energy, the nature of possible future singularities, the effect of higher order curvature terms to avoid a Big Rip singularity, and approaches to modifying gravity which leads to a late-time accelerated expansion without recourse to a new form of dark energy.

Recently, a new framework for solving the hierarchy problem has been proposed which does not rely on low energy supersymmetry or technicolor. The gravitational and gauge interactions unite at the electroweak scale, and the observed weakness of gravity at long distances is due the existence of large new spatial dimensions. In this letter, we show that this framework can be embedded in string theory. These models have a perturbative description in the context of type I string theory. The gravitational sector consists of closed strings propagating in the higher-dimensional bulk, while ordinary matter consists of open strings living on D3-branes. This scenario raises the exciting possibility that the LHC and NLC will experimentally study ordinary aspects of string physics such as the production of narrow Regge-excitations of all standard model particles, as well more exotic phenomena involving strong gravity such as the production of black holes. The new dimensions can be probed by events with large missing energy carried off by gravitons escaping into the bulk. We finally discuss some important issues of model building, such as proton stability, gauge coupling unification and supersymmetry breaking.

We study the vacuum structure and dyon spectrum of N = 2 supersymmetric gauge theory in four dimensions, with gauge group SU (2). The theory turns out to have remarkably rich and physical properties which can nonetheless be described precisely; exact formulas can be obtained, for instance, for electron and dyon masses and the metric on the moduli space of vacua. The description involves a version of Olive-Montonen electric-magnetic duality.

This paper presents a new event generator, ALPGEN, dedicated to the study of multiparton hard processes in hadronic collisions. The code performs, at the leading order in QCD and EW interactions, the calculation of the exact matrix elements for a large set of parton-level processes of interest in the study of the Tevatron and LHC data. The current version of the code describes the following final states: (W → ff ′ )QQ + N jets (Q being a heavy quark, and f = ℓ, q), with N ≤ 4; (Z/γ * → ff ) QQ + N jets (f = ℓ, ν), with N ≤ 4; (W → ff ′ ) + charm + N jets (f = ℓ, q, N ≤ 5); (W → ff ′ ) + N jets (f = ℓ, q) and (Z/γ * → ff ) + N jets (f = ℓ, ν), with N ≤ 6; nW + mZ + lH + N jets, with n + m + l + N ≤ 8, N ≤ 3, including all 2-fermion decay modes of W and Z bosons, with spin correlations; QQ + N jets, with t → bff ′ decays and relative spin correlations included if Q = t, and N ≤ 6; QQQ ′ Q ′ + N jets, with Q and Q ′ heavy quarks (possibly equal) and N ≤ 4; HQQ + N jets, with t → bff ′ decays and relative spin correlations included if Q = t and N ≤ 4; N jets, with N ≤ 6. Parton-level events are generated, providing full information on their colour and flavour structure, enabling the evolution of the partons into fully hadronised final states.

The Large Hadron Collider presents an unprecedented opportunity to probe the realm of new physics in the TeV region and shed light on some of the core unresolved issues of particle physics. These include the nature of electroweak symmetry breaking, the origin of mass, the possible constituent of cold dark matter, new sources of CP violation needed to explain the baryon excess in the universe, the possible existence of extra gauge groups and extra matter, and importantly the path Nature chooses to resolve the hierarchy problem -is it supersymmetry or extra dimensions. Many models of new physics beyond the standard model contain a hidden sector which can be probed at the LHC. Additionally, the LHC will be a top factory and accurate measurements of the properties of the top and its rare decays will provide a window to new physics. Further, the LHC could shed light on the origin of neutralino masses if the new physics associated with their generation lies in the TeV region. Finally, the LHC is also a laboratory to test the hypothesis of TeV scale strings and D brane models. An overview of these possibilities is presented in the spirit that it will serve as a companion to the Technical Design Reports (TDRs) by the particle detector groups ATLAS and CMS to facilitate the test of the new theoretical ideas at the LHC. Which of these ideas stands the test of the LHC data will govern the course of particle physics in the subsequent decades.

X -ray radiographic absorption imaging is an invaluable tool in medical diagnostics and materials science. For biological tissue samples, polymers or fibre composites, however, the use of conventional X-ray radiography is limited due to their weak absorption. This is resolved at highly brilliant X-ray synchrotron or micro-focus sources by using phase-sensitive imaging methods to improve the contrast 1,2 . However, the requirements of the illuminating radiation mean that hard-X-ray phase-sensitive imaging has until now been impractical with more readily available X-ray sources, such as X-ray tubes. In this letter, we report how a setup consisting of three transmission gratings can efficiently yield quantitative differential phase-contrast images with conventional X-ray tubes. In contrast with existing techniques, the method requires no spatial or temporal coherence, is mechanically robust, and can be scaled up to large fields of view. Our method provides all the benefits of contrast-enhanced phase-sensitive imaging, but is also fully compatible with conventional absorption radiography. It is applicable to X-ray medical imaging, industrial non-destructive testing, and to other low-brilliance radiation, such as neutrons or atoms.

Gigaelectron volt (GeV) electron accelerators are essential to synchrotron radiation facilities and free-electron lasers, and as modules for high-energy particle physics. Radiofrequency-based accelerators are limited to relatively low accelerating fields (10–50 MV m -1 ), requiring ...

This thesis aims to make precise the microscopic understanding of Hawking radiation from the D1/D5 black hole. We present an explict construction of all the shortmultiplets of the N = (4, 4) SCFT on the symmetric productT 4 /S(Q 1 Q 5 ). An investigation of the symmerties of this SCFT enables us to make a one-to-one correspondence beween the supergravity moduli and the marginal opeerators of the SCFT. We analyse the gauge theory dynamics of the splitting of the D1/D5 system into subsystems and show that it agrees with supergravity.

We present a novel approach to the detection of weak magnetic fields that takes advantage of recently developed techniques for the coherent control of solid-state electron spin quantum bits. Specifically, we investigate a magnetic sensor based on Nitrogen-Vacancy centers in room-temperature diamond. We discuss two important applications of this technique: a nanoscale magnetometer that could potentially detect precession of single nuclear spins and an optical magnetic field imager combining spatial resolution ranging from micrometers to millimeters with a sensitivity approaching few femtotesla/Hz$^{1/2}$.

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We present the first complete next-to-next-to-leading order analysis of the Standard Model Higgs potential. We computed the two-loop QCD and Yukawa corrections to the relation between the Higgs quartic coupling (λ) and the Higgs mass (M h ), reducing the theoretical uncertainty in the determination of the critical value of M h for vacuum stability to 1 GeV. While λ at the Planck scale is remarkably close to zero, absolute stability of the Higgs potential is excluded at 98% C.L. for M h < 126 GeV. Possible consequences of the near vanishing of λ at the Planck scale, including speculations about the role of the Higgs field during inflation, are discussed.

Physics at the Large Hadron Collider (LHC) and the International e + e − Linear Collider (ILC) will be complementary in many respects, as has been demonstrated at previous generations of hadron and lepton colliders. This report addresses the possible interplay between the LHC and ILC in testing the Standard Model and in discovering and determining the origin of new physics. Mutual benefits for the physics programme at both machines can occur both at the level of a combined interpretation of Hadron Collider and Linear Collider data and at the level of combined analyses of the data, where results obtained at one machine can directly influence the way analyses are carried out at the other machine. Topics under study comprise the physics of weak and strong electroweak symmetry breaking, supersymmetric models, new gauge theories, models with extra dimensions, and electroweak and QCD precision physics. The status of the work that has been carried out within the LHC / LC Study Group so far is summarised in this report. Possible topics for future studies are outlined. 5.4.1 Non-decoupling effect in sfermion-chargino/neutralino couplings 299 5.4.2 Correlations of flavour and collider physics within supersymmetry306 5.4.3 Supersymmetric lepton flavour violation at LHC and LC . . . 310 5.4.4 Detection difficulties for MSSM and other SUSY models for special boundary conditions32 5.5 Determination of mSUGRA parameters and discrimination between SUSY breaking scenarios325 5.5.

The DØ experiment enjoyed a very successful data-collection run at the Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has been upgraded to take advantage of improvements to the Tevatron and to enhance its physics capabilities. We describe the new elements of the detector, including the silicon microstrip tracker, central fiber tracker, solenoidal magnet, preshower detectors, forward muon detector, and forward proton detector. The uranium/liquid-argon calorimeters and central muon detector, remaining from Run I, are discussed briefly. We also present the associated electronics, triggering, and data acquisition systems, along with the design and implementation of software specific to DØ.

We review the particle theory origin of inflation and curvaton mechanisms for generating large scale structures and the observed temperature anisotropy in the cosmic microwave background (CMB) radiation. Since inflaton or curvaton energy density creates all matter, it is important to understand the process of reheating and preheating into the relevant degrees of freedom required for the success of Big Bang Nucleosynthesis. We discuss two distinct classes of models, one where inflaton and curvaton belong to the hidden sector, which are coupled to the Standard Model gauge sector very weakly. There is another class of models of inflaton and curvaton, which are embedded within Minimal Supersymmetric Standard Model (MSSM) gauge group and beyond, and whose origins lie within gauge invariant combinations of supersymmetric quarks and leptons.

During 2004, four divisions of the American Physical Society commissioned a study of neutrino physics to take stock of where the field is at the moment and where it is going in the near and far future. Several working groups looked at various aspects of this vast field. The summary was published as a main report entitled "The Neutrino Matrix" accompanied by short 50 page versions of the report of each working group. Theoretical research in this field has been quite extensive and touches many areas and the short 50 page report [1] provided only a brief summary and overview of few of the important points. The theory discussion group felt that it may be of value to the community to publish the entire study as a white paper and the result is the current article. After a brief overview of the present knowledge of neutrino masses and mixing and some popular ways to probe the new physics implied by recent data, the white paper summarizes what can be learned about physics beyond the Standard Model from the various proposed neutrino experiments. It also comments on the impact of the experiments on our understanding of the origin of the matter-antimatter asymmetry of the Universe and the basic nature of neutrino interactions as well as the existence of possible additional neutrinos. Extensive references to original literature are provided.

We compare different procedures for combining fixed-order tree-level matrixelement generators with parton showers. We use the case of W-production at the Tevatron and the LHC to compare different implementations of the so-called CKKW and MLM schemes using different matrix-element generators and different parton cascades. We find that although similar results are obtained in all cases, there are important differences. ARIADNE the Lönnblad scheme; HELAC the MLM scheme, but will show results with the PYTHIA shower; MADEVENT uses a variant of the MLM scheme, based on the CKKW parametrization of the multiparton phase-space; SHERPA, finally, implements the CKKW scheme. This list of codes therefore covers a broad spectrum of alternative approaches and, in particular, includes all the programs used as reference event generators for multijet production by the Tevatron and LHC experimental collaborations; for those, we show results relative to publically available versions, therefore providing valuable information on the systematics involved in the generation of multijet configurations by the experiments. A preliminary study, limited to the ALPGEN, ARIADNE and SHERPA codes, was presented in .

We find the gravity solution corresponding to a large number of NS or D fivebranes wrapped on a two sphere so that we have pure N = 1 super Yang-Mills in the IR. The supergravity solution is smooth, it shows confinement and it breaks the U(1) R chiral symmetry in the appropriate way. When the gravity approximation is valid the masses of glueballs are comparable to the masses of Kaluza Klein states on the fivebrane, but if we could quantize strings on this background it looks like we should be able to decouple the KK states.

The muon anomalous magnetic moment is one of the most precisely measured quantities in particle physics. In a recent experiment at Brookhaven it has been measured with a remarkable 14-fold improvement of the previous CERN experiment reaching a precision of 0.54ppm. Since the first results were published, a persisting "discrepancy" between theory and experiment of about 3 standard deviations is observed. It is the largest "established" deviation from the Standard Model seen in a "clean" electroweak observable and thus could be a hint for New Physics to be around the corner. This deviation triggered numerous speculations about the possible origin of the "missing piece" and the increased experimental precision animated a multitude of new theoretical efforts which lead to a substantial improvement of the prediction of the muon anomaly aµ = (gµ − 2)/2. The dominating uncertainty of the prediction, caused by strong interaction effects, could be reduced substantially, due to new hadronic cross section measurements in electron-positron annihilation at low energies. Also the recent electron g − 2 measurement at Harvard contributes substantially to the progress in this field, as it allows for a much more precise determination of the fine structure constant α as well as a cross check of the status of our theoretical understanding.

In these two lectures, we will address the topic of the creation of small black holes during particle collisions in a ground-based accelerator, such as LHC, in the context of a higher-dimensional theory. We will cover the main assumptions, criteria and estimates for their creation, and we will discuss their properties after their formation. The most important observable effect associated with their creation is likely to be the emission of Hawking radiation during their evaporation process. After presenting the mathematical formalism for its study, we will review the current results for the emission of particles both on the brane and in the bulk. We will finish with a discussion of the methodology that will be used to study these spectra, and the observable signatures that will help us identify the black-hole events.

Gluon fusion is the main production mechanism for Higgs particles at the LHC. We present the QCD corrections to the fusion cross sections for the Higgs boson in the Standard Model, and for the neutral Higgs bosons in the minimal supersymmetric extension of the Standard Model. The QCD corrections are in general large and they increase the cross sections signicantly. I n t w o steps preceding the calculation of the production processes, we determine the QCD radiative corrections to Higgs decays into two photons and gluons.

We develop a simple description of models where electroweak symmetry breaking is triggered by a light composite Higgs, which emerges from a strongly-interacting sector as a pseudo-Goldstone boson. Two parameters fully characterize these models: m ρ , the mass scale of the new resonances and g ρ , their coupling. An effective low-energy Lagrangian approach proves to be useful for LHC and ILC phenomenology below the scale m ρ . We identify two classes of operators: those that are genuinely sensitive to the new strong force and those that are sensitive to the spectrum of the resonances only. Phenomenological prospects for the LHC and the ILC include the study of high-energy longitudinal vector boson scattering, strong double-Higgs production and anomalous Higgs couplings. We finally discuss the possibility that the top quark could also be a composite object of the strong sector. responsible for electroweak symmetry breaking. If no new states are observed, or if the resonances are too broad to be identified, then our tests can be used to investigate whether the Higgs is weakly coupled or is an effective particle emerging from a strongly-interacting sector, whose discovery has been barely missed by direct searches at the LHC. This paper is organized as follows. In sect. 2, we define the SILH and construct the low-energy effective theory that describes its interactions with the SM fields. In sect. 3, we discuss how this effective Lagrangian is related to specific models previously proposed in the literature, like the Holographic Higgs and the Little Higgs. Then we describe in sect. 4, how the SILH can be tested in collider experiments. In sect. 5, we extend our analysis to the case of a composite top quark and finally we summarize our results and draw our conclusions in sect. 6.

Preprint submitted to Elsevier Science 5.1 The first-order curvature perturbation 67 5.2 Reheating after inflation 69 5.3 The second-order curvature perturbation and non-Gaussianity during inflation 70 5.4 Reheating after inflation 75 5.5 Post-inflationary evolution of the second-order curvature perturbation 76 6 The curvaton scenario 78 6.1 Generating the curvature perturbation at linear order 79 6.2 Second-order curvature perturbation from the curvaton fluctuations 82 7 The inhomogeneous reheating scenario: δΓ = 0 85 7.1 Generating the curvature perturbation at linear order from decay rate fluctuations 86 7.2 Second-order curvature perturbation from inhomogeneous reheating 87 8 Non-linearities in the gravitational potential 89 8.1 The standard scenario 90 8.2 The curvaton scenario 93 8.3 The inhomogeneous reheating scenario 94 8.4 Second-order temperature fluctuations on large scales and the correct definition of the measured f NL 96 9

In this paper we present FeynRules, a new Mathematica package that facilitates the implementation of new particle physics models. After the user implements the basic model information ( e.g., particle content, parameters and Lagrangian), FeynRules derives the Feynman rules and stores them in a generic form suitable for translation to any Feynman diagram calculation program. The model can then be translated to the format specific to a particular Feynman diagram calculator via FeynRules translation interfaces. Such interfaces have been written for CalcHEP/CompHEP, FeynArts/FormCalc, MadGraph/MadEvent and Sherpa, making it possible to write a new model once and have it work in all of these programs. In this paper, we describe how to implement a new model, generate the Feynman rules, use a generic translation interface, and write a new translation interface. We also discuss the details of the FeynRules code.

We present a detailed investigation of chaotic inflation models which feature two scalar fields, such that one field (the inflaton) rolls while the other is trapped in a false vacuum state. The false vacuum becomes unstable when the magnitude of the inflaton field falls below some critical value, and a first or second order transition to the true vacuum ensues. Particular attention is paid to the case, termed 'Hybrid Inflation' by Linde, where the false vacuum energy density dominates, so that the phase transition signals the end of inflation. We focus mostly on the case of a second order transition, but treat also the first order case and discuss bubble production in that context for the first time.

Angular differential imaging is a high-contrast imaging technique that reduces quasistatic speckle noise and facilitates the detection of nearby companions. A sequence of images is acquired with an altitude/azimuth telescope while the instrument field derotator is switched off. This keeps the instrument and telescope optics aligned and allows the field of view to rotate with respect to the instrument. For

The Hubble expansion of galaxies, the 2.73 K blackbody radiation background and the cosmic abundances of the light elements argue for a hot, dense origin of the universe -the standard Big Bang cosmology -and enable its evolution to be traced back fairly reliably to the nucleosynthesis era when the temperature was of O (1) MeV corresponding to an expansion age of O (1) sec. All particles, known and hypothetical, would have been created at higher temperatures in the early universe and analyses of their possible effects on the abundances of the synthesized elements enable many interesting constraints to be obtained on particle properties. These arguments have usefully complemented laboratory experiments in guiding attempts to extend physics beyond the Standard SU(3) c ⊗SU(2) L ⊗U(1) Y Model, incorporating ideas such as supersymmetry, compositeness and unification. We first present a pedagogical account of primordial nucleosynthesis, discussing both theoretical and observational aspects, and then proceed to discuss such constraints in detail, in particular those pertaining to new massless particles and massive unstable particles.

We formulate and prove a QCD factorization theorem for hard exclusive electroproduction of mesons in QCD. The proof is valid for the leading power in Q and all logarithms. This generalizes previous work on vector meson production in the diffractive region of small x. The amplitude is expressed in terms of off-diagonal generalizations of the usual parton densities. The full theorem applies to all kinds of meson and not just to vector mesons. The parton densities used include not only the ordinary parton density, but also the helicity density (g 1 or ∆q) and the transversity density (h 1 or δq), and these can be probed by measuring the polarization of the produced mesons with unpolarized protons.