A Uv Complete Composite Higgs Model For Electroweak Symmetry Breaking

The Large Hadron Collider is currently collecting data. One of the main goals of the experiment is to find evidence of the mechanism responsible for the breaking of the electroweak symmetry. There are many different models attempting to explain this breaking and traditionally most of them involve the use of supersymmetry near the scale of the breaking. This work is focused on exploring a viable model that is not based on a weakly coupled low scale supersymmetry sector to explain the electroweak symmetry breaking. We build a model based on a new strong interaction, in the fashion of theories commonly called "technicolor", name that is reminiscent of one of the first attempts of explaining the electroweak symmetry breaking using a strong interaction similar to the one whose charges are called colors. We explicitly study the minimal model of conformal technicolor, an SU(2) gauge theory near a strongly cou- pled conformal fixed point, with conformal symmetry softly broken by technifermion mass terms. Conformal symmetry breaking triggers chiral symmetry breaking in the pattern SU(4) -->Sp(4), which gives rise to a pseudo-Nambu-Goldstone boson that can act as a composite Higgs boson. There is an additional composite pseudoscalar A with mass larger than m[subscript h] and suppressed direct production at LHC. We discuss the electroweak fit in this model in detail. A good fit requires fine tuning at the 10% level. We construct a complete, realistic, and natural UV completion of the model, that explains the origin of quark and lepton masses and mixing angles. We embed conformal technicolor in a supersymmetric theory, with supersymmetry broken at a high scale. The effective theory below the supersymmetry breaking scale is minimal conformal technicolor with an additional light technicolor gaugino that might give rise to an additional pseudo Nambu-Goldstone boson that is observable at the LHC.

This volume contains the talks given at the above workshop which was devoted to discussing the newest developments in various models of electroweak symmetry breaking forming the basis of modern particle physics. It includes various aspects of Higgs physics and condensate models embodying dynamical symmetry breaking.

The Hierarchy Problem is arguably the most important guiding principle concerning the extension to high-energy scales of the Standard Model (SM) of Fundamental Interactions. Every scenario for addressing this issue unavoidably predicts new physics in the TeV energy range, which is currently being probed directly by the LHC experimental program. Among the possible solutions to the Hierarchy Problem, the scenario of a composite Higgs boson is a very simple idea and a rather plausible picture has emerged over the years by combining the following ingredients: First, the Higgs must be a (pseudo-) Nambu-Goldstone boson, rather than a generic hadron of the new strong sector. Second, through the so-called ‘partial compositeness’, SM particles mix with strong sector resonances with suitable quantum numbers, so that they become a linear combination of elementary and composite degrees of freedom. Recently, general descriptions of the Composite Higgs Scenario were developed which successfully capture the relevant features of this theoretical framework in a largely model-independent way. The present book provides a concise and illustrative introduction to the subject for a broad audience of graduate students and non-specialist researchers in the fields of particle, nuclear and gravitational physics.

Strong dynamics constitutes one of the pillars of the standard model of particle interactions, and it accounts for the bulk of the visible matter in the universe made by ordinary protons and neutrons. It is therefore a well posed question to ask if the rest of the universe can be described in terms of new highly natural four-dimensional strongly coupled theories. The main goal of this lecture-based primer is to provide a coherent overview of how new strong dynamics can be employed to address the relevant challenges in particle physics and cosmology from composite Higgs dynamics to dark matter and inflation. We will first introduce the topic of dynamical breaking of the electroweak symmetry also known as technicolor. The knowledge of the phase diagram of strongly coupled theories plays a fundamental role when trying to construct viable extensions of the standard model. Therefore we present the state-of-the-art of the phase diagram for gauge theories as function of the number of colors, flavors, matter representation and gauge group. Recent extensions of the standard model featuring minimal technicolor theories are then introduced as relevant examples. We finally show how technicolor or in general new strongly coupled theories can lead to natural candidates of composite dark matter and inflation.

With the Large Hadron Collider collecting data, both the pursuit of novel detection techniques and the exploration of new ideas are more important than ever. Novel detection techniques are essential in order for the community to garner the most worth from the machine. New ideas are needed both to expand the boundaries of what could be observed and to foster the creative mindset of the community that moves particle physics into fascinating, and often unexpected, directions. Discovering whether electroweak symmetry is broken strongly or weakly is one of the most pressing questions to be answered. Exploring the possibility of strong electroweak symmetry breaking is the topic of this work. The first of two major sectors in this work concerns the theory of conformal technicolor. We present the low energy minimal model for conformal technicolor and verify that it can satisfy current constraints from experiment. We will also provide a UV completion for this model, which realistically extends the sector with high-energy supersymmetry. Two complete models of flavor are presented. This is the first example of a complete, consistent model of strong electroweak symmetry breaking. The second of the two sectors discusses experimental signatures arising in a large class of general technicolor models at the Large Hadron Collider. The possible existence of narrow scalar states that can be produced via gluon-gluon fusion is first discussed. These states can decay into exotic final states of multiple electroweak gauge bosons, third generation particles and even light composite Higgs particles. A two Higgs doublet model is proposed as an effective way to model these exciting states. Lastly, we discuss the array of possible final states and their possible discovery.

The Standard Model (SM) is the most successful theory describing the particle interactions. Its predictions, incredibly precise, agree very well with the experimental data. The last proof being the discovery of the Higgs boson in 2012, which is at the origin of the mass of the other particles, thus essential to the theory. However, the SM cannot explain everything: - Experiments have confirmed a mass for the neutrinos, which the SM does not provide. -The gravitational interactions are not a part of the SM. -The dark matter, hypothetical particle to explain the astrophysics observations, is not taken into account in the SM - The Higgs Mechanism that generates a mass to the boson is ad-hoc via the introduction of the Higgs potential. The Higgs mass also suffers from the quadratic divergences of new physics. Those reasons push us to believe that the SM is just the low energy manifestation of a more fundamental theoy. The main subject of the thesis are the Composite Higgs Models, which principaly try to solve the last issue of the above list. In this class of models, the higgs Boson, and all its ineractions, are replace by a new fermionic sector very similar to Quantum ChromoDynamic (QCD). For that purpose, new fermions called technifermions are introduced and charged under a new color dubbed technicolor. Like the color in QCD, the technicolor theory confines at low energy and a condensate breaks its global symmetries. This generates Goldstone bosons which can play the role of the SM Higgs boson. By its bound state nature, the new Higgs boson has no more issues with the quantum correction of its mass. In this scenario the new strong interaction gives a dynamical origin to the Higgs potential. Nontheless, challenges appear if we want to generate a mass for the SM fermions. The paradigm of Partial Compositness try to overcome this issue and postulate a linear mixing between the SM fermions and technibaryons, fermionic bound state of three technifermions, like the quarks forming the proton.

Almost all theories of fundamental interactions are nowadays based on the gauge concept. Starting with the historical example of quantum electrodynamics, we have been led to the successful unified gauge theory of weak and electromagnetic interactions, and finally to a non abelian gauge theory of strong interactions with the notion of permanently confined quarks. The. early theoretical work on gauge theories was devoted to proofs of renormalizability, investigation of short distance behaviour, the discovery of asymptotic freedom, etc . . , aspects which were accessible to tools extrapolated from renormalised perturbation theory. The second phase of the subject is concerned with the problem of quark confinement which necessitates a non-perturbative understanding of gauge theories. This phase has so far been marked by the introduc tion of ideas from geometry, topology and statistical mechanics in particular the theory of phase transitions. The 1979 Cargese Institute on "Recent Developments on Gauge Theories" was devoted to a thorough discussion of these non-perturbative, global aspects of non-abelian gauge theories. In the lectures and seminars reproduced in this volume the reader wilf find detailed reports on most of the important developments of recent times on non perturbative gauge fields by some of the leading experts and innovators in this field. Aside from lectures on gauge fields proper, there were lectures on gauge field concepts in condensed matter physics and lectures by mathematicians on global aspects of the calculus of variations, its relation to geometry and topology, and related topics.

With the discovery of the Higgs boson, the LHC experiments have closed the most important gap in our understanding of fundamental interactions, confirming that such interactions between elementary particles can be described by quantum field theory, more specifically by a renormalizable gauge theory. This theory is a priori valid for arbitrarily high energy scales and does not require an ultraviolet completion. Yet, when trying to apply the concrete knowledge of quantum field theory to actual LHC physics - in particular to the Higgs sector and certain regimes of QCD - one inevitably encounters an intricate maze of phenomenological know-how, common lore and other, often historically developed intuitions about what works and what doesn’t. These lectures cover three aspects to help understand LHC results in the Higgs sector and in searches for physics beyond the Standard Model: they discuss the many facets of Higgs physics, which is at the core of this significantly expanded second edition; then QCD, to the degree relevant for LHC measurements; as well as further standard phenomenological background knowledge. They are intended to serve as a brief but sufficiently detailed primer on LHC physics to enable graduate students and all newcomers to the field to find their way through the more advanced literature, and to help those starting to work in this very timely and exciting field of research. Advanced readers will benefit from this course-based text for their own lectures and seminars. .

The Standard Model (SM) of particle physics is a monumental achievement which very accurately describes almost all observed phenomena. However, the Standard Model is not complete without a mechanism for electroweak symmetry breaking. The historically conventional mechanism for electroweak symmetry breaking is the Higgs mechanism. However, the Higgs boson, as described in the Standard Model, has not yet been discovered and in fact is bounded to exist in a fairly narrow mass range. In addition, the SM Higgs suffers from fine-tuning issues associated with the fact that it is both an elementary scalar and that it has no symmetry to protect its mass from quantum corrections. Due to these problems, many models of physics beyond the SM have been proposed which can break electroweak symmetry and also avoid some or all of these fine-tuning issues. We examine a scenario where the Higgs is a bound state of an approximate conformal field theory, and has a scaling dimension greater than one. We show that such an unparticle Higgs (or Unhiggs) can still break electroweak symmetry and unitarize WW and fermion fermion scattering, but its gauge couplings are suppressed. We investigate the phenomenological consequences of the Unhiggs, and show that it can more easily avoid LEP bounds due to its suppressed gauge couplings. We also place theoretical and observational bounds on certain parameters in the model. Finally, we illustrate that an Unhiggs model has a reduced sensitivity of the weak scale to the cutoff, and can thus provide a solution to the little hierarchy problem.