HIP Theory Project: Laws of Nature and Condensed Particle Matter @ LHC
The Standard Model (SM) of elementary particle physics has been tested extensively in a large number of experiments and found to agree with these, with the exception of massive neutrinos. In respect to the future particle physics experiments at the LHC there are two important aspects of SM open for more thorough tests than before: these are on one hand the electroweak superconductivity, i.e. the Higgs physics, and the physics of hot QCD matter. The Higgs sector of SM appears very finely tuned, and many theorists take this as an indication that the Standard Model is an effective theory valid only below the TeV energy range, above which it should be replaced by a more fundamental theory. Experimental evidence for physics beyond the Standard Model has begun to accumulate with measurements of neutrino masses. Hints towards a more fundamental theory are expected when experimental data from LHC is analyzed and the nature of electroweak symmetry breaking sector is revealed. Proposed beyond the Standard Model (BSM) physics must be carefully considered against all experimental signatures.
The ultrarelativistic heavy ion collisions (URHIC) group in Jyväskylä and Helsinki has pioneered many phenomenology studies of strongly interacting QCD matter, Quark Gluon Plasma (QGP), over the years. Controlled predictions for various observables measurable soon in the ALICE experiment at LHC, currently in the BNL-RHIC and previously in the CERN-SPS experiments have been made with the basic computational tools of perturbative QCD (pQCD), relativistic hydrodynamics and effective field theories at finite temperature. For instance, our RHIC-tested multiplicity predictions have affected the LHC/ALICE data simulations, and our QCD-analysis of the nuclear parton distributions (EKS98) has become a standard reference in the field.
Considering BSM physics, we will focus mainly on one hand on the symmetry breaking issues, and on the other hand on flavour physics, including rare decays and CP violation. The theoretical frameworks of our studies will be supersymmetric models, models with extra dimensions, and models with new types of gauge interactions (e.g. technicolor, extended gauge models and noncommutative models). In general we aim to study the detailed collider phenomenology in the classes of theories mentioned, and identify smoking gun signatures for a particular theory.
In flavour physics we currently consider the lepton flavour violation in view of the improving low energy measurements and their implications at LHC. In particular, we study lepton decays and their correlation with low energy experiments. Also the effect of neutrino mass and mixing measurements on flavour violating processes are being investigated. This will test theories of neutrino mass generation. We are also studying the possibility to observe lepton number violation in sneutrino-antisneutrino mixing at LHC. We found earlier observation of the mixing possible in (experimentally cleaner) linear collider environment. The new more precise factorization methods are being applied to flavour violating B-meson decays. Detection of supersymmetric partners of doubly charged particles, typical for many BSM theories, is under study, especially separation at LHC of the signal from similar final state signal in minimal supersymmetric standard model (MSSM). Other supersymmetric particle signatures being investigated include the general phenomenology of stau as the next to the lightest supersymmetric particle. The experimental verification or falsification of such particle seems possible with a few 1/fb at LHC.
In the noncommutative field theory prescription of nature, a new way to break the electroweak symmetry is under study. The attempts made so far are not fulfilling the unitarity constraints, and thus suffer from inconsistencies. Higgs detection in the so-called MSSM wedge region requiring at the same time that the lightest supersymmetric particle forms dark matter of the universe has been investigated in collaboration with local CMS experimentalists. Currently dark matter in several BSM models is under study. In connection with dark matter and TeV scale physics, the Helsinki group co-organises next year a two month program in Nordita, Stockholm.
In the URHIC phenomenology studies, we are currently preparing various predictions for the LHC Pb+Pb collisions, e.g. how the high-pT hadron spectra could serve as a tomographic tool for QCD matter, and what is the amount of elliptic flow. We are also developing a Monte Carlo simulation of partonic energy losses at RHIC and LHC, and studying the details of QCD matter decoupling dynamics. To develop our hydrodynamical framework further, we plan to include viscous effects, and eventually reach a fully 1+3 dimensional hydro code. Computation of electromagnetic emission at RHIC and LHC, as well as heavy quark energy losses are also on our work-list. To examine specific signals and properties of the QGP in URHIC at the LHC, nuclear parton distribution functions (nPDFs) must be known. Our global analysis of the QCD-evolving nPDFs (EKS98) is being improved by including further constraints for nuclear gluons from the RHIC d+Au data. Future prospects for probing the nuclear gluons via heavy quark production at RHIC and LHC will be studied in detail. A next-to-leading global analysis of the nPDFs will be constructed.
In addition to URHIC phenomenology, we will concentrate on the studies of phase diagrams of strongly interacting theories using effective theories. The intertwining of deconfinement and chiral symmetry breaking at and away from the chiral limit both in finite temperature and finite densisites is currently being studied. Our current investigations also consider diquark condensation and applications for compact stars. The methods of dimensional reduction have been applied to determine the QCD pressure up to the final perturbatively calculable terms, and computation of the nonperturbative contribution is in progress. Similar techniques can be also applied to study the electroweak phase transition in different beyond the standard model frameworks; knowing the order of the transition is imperative for the electroweak baryogenesis scenario. Recent developments suggest that some strongly interacting gauge theories can be analysed through a mathematical duality with five dimensional classical gravity in anti-deSitter space when the number of gauge degrees of freedom is taken to be large. Phenomenological implications of this AdS/CFT correspondence have been investigated mainly for QCD, but applications for technicolor theories will be considered in the future.