New Approaches to Electroweak Symmetry Breaking Workshop Description New Approaches to EWSB

New Approaches to Electroweak Symmetry Breaking

Organizers: Csaba Cs´aki,(607) 254 8935, [email protected] Konstantin Matchev, (352) 392 5709, [email protected]ﬂ.edu John Terning (505) 665 0437, [email protected]

Workshop Description The origin of electroweak symmetry breaking (EWSB) is among the most intriguing problems facing particle physics today. The main question, “What breaks electroweak symmetry?” allows several possible answers, but each one brings up a host of new questions. If EWSB is due to a fundamental scalar particle (a Higgs boson), then why is the weak scale stable under quantum corrections? In the standard model (SM) quantum corrections tend to drive the weak scale up to the highest possible scale in the theory, e.g. the Planck scale. This instability is known as the hierarchy problem. If the Higgs boson exists, is it a fundamental or a composite object? Does the Higgs boson give rise to the masses of both matter and gauge particles? Does the Higgs sector preserve CP symmetry? If EWSB is due to something else, then why does it not affect precision electroweak observables much differently than a SM Higgs boson, and what is the mechanism of unitarizing gauge boson scattering at high energies? For many years there were only two approaches to solving the hierarchy problem of the SM: supersymmetry and technicolor. In the last few years there has been an explosion of new ideas including: large extra dimensions, warped extra dimensions, gauge extensions of the MSSM, fat Higgs, little Higgs, the Higgs as a gauge component, and Higgsless models. Each of these approaches involves very distinct possibilities for physics beyond the standard model. The aim of the workshop will be to study the new scenarios, identify the relevant experimental signatures in each case, and propose strategies for experimentally testing these ideas at the Large Hadron Collider (LHC) and the next Linear Collider (NLC). Such a discussion is very timely as the upcoming particle physics experiments at the LHC (turning on in 2007) and ultimately at the NLC, are expected to definitively address the EWSB puzzle. The purpose of this workshop would be to bring together experts in diverse areas within these new approaches to EWSB in order to synthesize the main predictions of these models, establish search strategies and methods of discriminating between different alternatives, im- prove the models, and hopefully stimulate new creative ideas spawning further new directions of research. It will also be helpful to include some experts on SM and MSSM Higgs physics and collider phenomenology since much of their expertise will be transferable to testing these new approaches.

New Approaches to EWSB Extra Dimensions There are various interesting possibilities to stabilize the Higgs against large radiative corrections if there are extra dimensions. In the large extra dimensions scenario the fundamental Planck scale is lowered all the way to the weak scale thus eliminating the hierarchy,

1 while in warped extra dimensions (Randall-Sundrum) the hierarchy problem is solved by localizing gravity and EWSB at different places in the extra dimension. Gauge Extensions of the MSSM A generic prediction of the minimal supersymmetric standard model (MSSM) is a light Higgs. The LEP bounds on the Higgs mass from direct searches, although not ruling out the MSSM, have lead to a certain tension between theory and experiment, motivating ideas leading us beyond the MSSM. Recent research shows that additional gauge structure beyond that of the MSSM can give extra contributions to the Higgs self-coupling and thus the Higgs mass, offering new possibilities for Higgs collider phenomenology in a supersymmetric framework. Fat Higgs A related idea is to have the Higgs and its self coupling originate from some confining dynamics, whereby the self-coupling could be larger than in the MSSM and the Higgs mass would again be raised. Little Higgs and Higgs as a gauge component A totally new approach to the hierarchy problem suggested in 2002 is to have the quadratic divergences canceled by same-spin partners of all the SM fields by the “little Higgs mechanism.” These models have been analyzed in depth in the last few years and simple viable models where corrections to electroweak precision measurements are small and a dark matter candidate exists due to “T-parity” have been proposed. Higgsless models. The most radical of these new approaches to EWSB is to totally eliminate the Higgs while keeping the theory weakly coupled. This can be done by breaking the symmetry via boundary conditions in extra dimensions.

Workshop Organization The preferred length of the workshop is five weeks, but four weeks is acceptable. The preferred dates are July 24 to August 27 with around 60 participants affiliated with the workshop over the four or five weeks. Two other less preferred but acceptable options are to start one week earlier or to start on June 19. Due to teaching requirements, the acceptable dates are June 19 to August 27, however these earlier dates involve two timing conflicts with international meetings. The first conflict is that the Lepton-Photon conference will be held from June 27 to July 5 in Sweden. The more serious of the potential conflicts is that SUSY 2005 will be held from July 18 to 23 in England. It is the conflict with SUSY 2005 that determined our earliest preferred date. There is no preference for a time adjacent to another meeting. All three organizers will be available throughout the whole workshop if held during the preferred dates given above. At least two organizers will be available at any given time during the acceptable dates We will encourage (and invite) applications in order to achieve a diverse set of participants. Such diversity would encompass participation from under-represented minorities and women, as well as geographical diversity, a diversity of institutions, a mix of post-docs and faculty, and inclusion of first-time Aspen Center visitors. Konstantin Matchev will be in charge of ensuring adequately diverse representation.

2 John Terning will be the contact person available for consultation. The following people have already indicated that they would be interested in attend- ing this workshop: Jonathan Bagger (Johns Hopkins), Gustavo Burdman (Sao Paulo), Marcela Carena (Fermilab), Zacharia Chacko (Arizona), Hsin-Chia Cheng (Harvard), Sekhar Chivukula (Michigan State), Bogdan Dobrescu (Fermilab), Jonathan Feng (Irvine), Paolo Gambino (CERN, Geneva), Howard Georgi (Harvard), Tony Gherghetta (Minnesota), Christophe Grojean (Saclay), Jack Gunion (UC Davis), Howie Haber (UC Santa Cruz), Lawrence Hall (UC Berkeley), David E. Kaplan (Johns Hopkins), Graham Kribs (IAS Princeton), Heather Logan (Madison), Steve Martin (Northern Illinois), Hitoshi Murayama (UC Berkeley), Ya- sunori Nomura (UC Berkeley), Maxim Perelstein (Cornell), Erich Poppitz (Toronto), Dave Rainwater (DESY, Hamburg), Thomas Rizzo (SLAC), Martin Schmaltz (Boston), Elizabeth Simmons (Michigan State), Witold Skiba (Yale), Shufang Su (Arizona), Raman Sundrum (Johns Hopkins), Tim Tait (Argonne), Carlos Wagner (Argonne), and James Wells (Michi- gan). Other possible key participants include Nima Arkani-Hamed (Harvard), Andy Cohen (Boston), Ann Nelson (Wasington), Alex Pomarol (Barcelona), Lisa Randall (Harvard), and Riccardo Rattazzi (CERN).