Symmetry Breaking Scenario Research Articles

LHC and the dark matter search: A review

The restart of the Large Hadron Collider (LHC) at CERN, foreseen in November 2009 after the incident of 2008, will finally open a new window on the physics at the TeV scale and will allow the discovery of the Standard Model Higgs boson, if it exists, or of possible alternative schemes for the spontaneous symmetry-breaking mechanism. Moreover the LHC Collider will hopefully provide an answer to one of the most compelling questions of today coming from astronomical observations, astrophysics and cosmic ray experiments: which is the particle physics candidate for the Dark Matter component of the Universe? Supersymmetry (SUSY) is a theoretically attractive scenario for physics beyond the Standard Model which can provide a suitable Dark Matter candidate in case R-parity is conserved. If SUSY is manifesting at the TeV scale, as favored by several arguments, it will be accessible at the LHC Collider within the first few years of data taking. In this paper search strategies for a generic SUSY models with R-parity conservation with the ATLAS detector are described. These inclusive search strategies are based on signatures with missing transverse momentum from undetected neutralinos, in addition to multiple hard jets and leptons. The corresponding discovery reach for the first fb −1 of integrated luminosity of ATLAS data will be presented together with a discussion of possible measurements needed to extract the masses of SUSY particles including the Lightest Supersymmetric Particle (LSP), which in various supersymmetric (SUSY) symmetry breaking scenarios, is the lightest neutralino χ ˜ 1 0 .

DYNAMICAL ELECTROWEAK SYMMETRY BREAKING IN STRING MODELS WITH D-BRANES

The possibility of dynamical electroweak symmetry breaking by strong coupling gauge interaction in models with D-branes in String Theory is examined. Instead of elementary scalar Higgs doublet fields, the gauge symmetry with strong coupling (technicolor) is introduced. As the first step of this direction, a toy model, which is not fully realistic, is concretely analyzed in some detail. The model consists of D-branes and anti-D-branes at orbifold singularities in (T2 × T2 × T2)/Z3 which preserves supersymmetry. Supersymmetry is broken through the brane supersymmetry breaking. It is pointed out that the problem of large S parameter in dynamical electroweak symmetry breaking scenario may be solved by natural existence of kinetic term mixings between hypercharge U(1) gauge boson and massive anomalous U(1) gauge bosons. The problems to be solved toward constructing more realistic models are clarified in the analysis.

Selected challenges in low-energy QCD and hadron physics

This presentation briefly addresses three basic issues of low-energy QCD: first, whether the Nambu-Goldstone scenario of spontaneous chiral symmetry breaking is well established; secondly, whether there is a dynamical entanglement of the chiral and deconfinement crossover transitions in QCD; and thirdly, what is the status of knowledge about the phase diagram of QCD at low temperature and non-zero baryon density. These three topics were injected as key words into a panel discussion at the Schladming school on Challenges in QCD. The following exposition reflects the style and character of the discussions, with no claim of completeness.

Duality in semi-inclusive pion electroproduction

We explore quark-hadron duality in semi-inclusive pion electroproduction on proton and neutron targets. Using the spin-flavor symmetric quark model, we compute ratios of $$\pi^+$$ and $$\pi^-$$ cross sections for both unpolarized and polarized scattering, and discuss realizations of duality in several symmetry breaking scenarios. The model calculations allow one to understand some of the key features of recent data on semi-inclusive pion production at low energies.

KAONIC ATOMS AT DAΦNE — THE SIDDHARTA EXPERIMENT

With precision X-ray spectroscopy of kaonic hydrogen at the DAΦNE electron-positron collider at Laboratori Nazionali di Frascati the chiral symmetry breaking scenario in the strangeness sector will be investigated by studying the K-p s-wave interaction at threshold. This is possible by observing the strong interaction induced shift and width of the 1s state in kaonic hydrogen atoms. The results of the first measurement at LNF with DEAR (DAΦNE Exotic Atom Research) will be given and the new SIDDHARTA (Silicon Drift Detector for Hadronic Atom Research with Timing Application) project will be described, which is aiming at a substantial improvement of the preceding DEAR result.

Very special (de Sitter) relativity

The effects of a nonvanishing value for the cosmological constant in the scenario of Lorentz symmetry breaking recently proposed by Cohen and Glashow (which they denote as very special relativity) are explored and observable consequences are pointed out.

Higgsless electroweak symmetry breaking at the LHC

While the Higgs model is the best studied scenario of electroweak symmetry breaking, a number strongly-coupled models exist, predicting new signatures. Recent studies of WW and WZ final states at the ATLAS and CMS experiments are summarized and expected sensitivities are presented within the frameworks of the technicolor straw-man model and the electroweak chiral Lagrangian.

Experimental studies on kaonic atoms at DAΦNE

With precise X-ray spectroscopy on kaonic hydrogen at the DAΦNE electron-positron collider at Laboratori Natzionali di Frascati the chiral symmetry breaking scenario in the strangeness sector will be investigated by studying the K − p and K − d s-wave interaction at threshold. The strong interaction induced shift and width of the kaonic hydrogen 1 s atomic state was measured with DEAR (DAΦNE Exotic Atom Research) and in future with SIDDHARTA (Silicon Drift Detector for Hadronic Atom Research with Timing Application) the kaonic hydrogen system will be measured with utmost precision. In addition, data for the K − d system will become available for the first time. Kaonic hydrogen together with precision measurements of kaonic helium will allow the study of the sub-threshold Λ(1405) resonance, which might act as a doorway for the formation of antikaon-mediated deeply bound nuclear states in light nuclei. Therefore, these precision measurements are a powerful tool to test chiral symmetry breaking in systems with strangeness.

Radiative breaking scenario for the GUT gauge symmetry

The origin of the GUT scale from the top down perspective is explored. The GUT gauge symmetry is broken by the renormalization group effects, which is an extension of the radiative electroweak symmetry breaking scenario to the GUT models. That is, in the same way as the origin of the electroweak scale, the GUT scale is generated from the Planck scale through the radiative corrections to the soft SUSY breaking mass parameters. This mechanism is applied to a perturbative SO(10) GUT model, recently proposed by us. In the SO(10) model, the relation between the GUT scale and the Planck scale can naturally be realized by using order one coupling constants.

Radiative electroweak symmetry breaking beyond leading logarithms

The top-quark Yukawa coupling is too large to permit radiative electroweak symmetry breaking to occur, to leading-logarithm order, for small values of y — the Higgs self-coupling. However, a large y solution leading to a viable Higgs mass of approximately 220 GeV does exist, and differs from conventional symmetry breaking by an approximately five-fold enhancement of the Higgs self-coupling. This scenario for radiative symmetry breaking is reviewed, and the order-by-order perturbative stability of this scenario is studied within the scalar-field theory projection of the Standard Model in which the Higgs self-coupling y represents the dominant Standard-Model coupling.PACS Nos.: 11.30.Qc, 11.10.Hi, 11.15.Tk, 12.15.Lk

Higgs mechanism for gravity

In this paper we elaborate on the idea of an emergent spacetime which arises due to the dynamical breaking of diffeomorphism invariance in the early universe. In preparation for an explicit symmetry breaking scenario, we consider nonlinear realizations of the group of analytical diffeomorphisms which provide a unified description of spacetime structures. We find that gravitational fields, such as the affine connection, metric, and coordinates, can all be interpreted as Goldstone fields of the diffeomorphism group. We then construct a Higgs mechanism for gravity in which an affine spacetime evolves into a Riemannian one by the condensation of a metric. The symmetry breaking potential is identical to that of hybrid inflation but with the noninflaton scalar extended to a symmetric second-rank tensor. This tensor is required for the realization of the metric as a Higgs field. We finally comment on the role of Goldstone coordinates as a dynamical fluid of reference.

Precision measurements on kaonic hydrogen and kaonic deuterium: DEAR and SIDDHARTA

The SIDDHARTA ( SI licon D rift D etector for H adronic A tom R esearch by T iming A pplication) experiment [J. Zmeskal, SIDDHARTA Technical Note IR-2 (2003); C. Curceanu (Petrascu), SID-DHARTA Technical Note IR-3 (2003)] represents the scientific and technical development of DEAR ( D AΦNE E xotic A tom R esearch) [S. Bianco et al., Rivista del Nuovo Cimento 22 (11) (1999) 1], as part of the program dedicated to exotic atoms at DAΦNE [G. Vignola, Proc. of the “5th European Particle Accelerator Conference”, Sitges, Eds. S. Myres et al., Institute of Physics Publishing, Bristol and Philadelphia (1996) 22]. The objective consists in an eV precision measurement of the kaonic hydrogen K α line shift and width induced by the strong interaction, and the first measurement of kaonic deuterium. These values will allow a precise determination of antikaon-nucleon scattering lengths and a better understanding of the chiral symmetry breaking scenario in the strangeness sector. DEAR performed the most precise measurement up to now on kaonic hydrogen, at the end of 2002. The SIDDHARTA collaboration is developing a new set of large area, triggerable X-ray Silicon Drift Detectors (SDD), which will improve by 2 orders of magnitude the background rejection, allowing to reach the proposed objectives. The results of DEAR, as well as the state of the art of the new setup are presented.

An Exact Analytic Continuation to Complex Replica Number in the Discrete Random Energy Model of Finite System Size

An expression for the moment of partition function valid for any finite system size N and complex power n (Re(n) > 0) is obtained for a simple spin glass model termed the discrete random energy model (DREM). We investigate the behavior of the moment in the thermodynamic limit N → ∞ using this expression, and find that a phase transition occurs at a certain real replica number when the temperature is sufficiently low, directly clarifying the scenario of replica symmetry breaking of DREM in the replica number space without using the replica trick. The validity of the expression is numerically confirmed. The distribution of zero points is also investigated for complex n (Re(n) > 0).

Overcoming System-Size Limitations in Spin Glasses

In order to overcome the limitations of small system sizes in spin-glass simulations, we investigate the one-dimensional Ising spin chain with power-law interactions. The model has the advantage over traditional higher-dimensional Hamiltonians in that a large range of system sizes can be studied. In addition, the universality class of the model can be changed by tuning the power law exponent, thus allowing us to scan from the mean-field to long-range and short-range universality classes. We illustrate the advantages of this model by studying the nature of the spin glass state where our results hint towards a replica symmetry breaking scenario. We also compute ground-state energy distributions and show that mean-field and non-mean-field models are intrinsically different.

Physics potential of ATLAS detector with high luminosity

The ATLAS detector is designed to exploit the full physics potential in the TeV energy region opened up by the Large Hadron Collider at a center of mass energy of 14 TeV with very high luminosities. The physics performance of the ATLAS detector on Higgs, extra-dimension and strong symmetry breaking scenario is summarized in this note. ATLAS experiment has great discovery potential for these new phenomena with high luminosity. Triple gauge couplings are very sensitive for probing new physics at TeV scale. We show that ATLAS can measure these couplings very precisely with high luminosity.

Exact Analytic Continuation with Respect to the Replica Number in the Discrete Random Energy Model of Finite System Size

An expression for the moment of partition function valid for any finite system size $N$ and complex power $n (\Re(n)>0)$ is obtained for a simple spin glass model termed the {\em discrete random energy model} (DREM). We investigate the behavior of the moment in the thermodynamic limit $N \to \infty$ using this expression, and find that a phase transition occurs at a certain real replica number when the temperature is sufficiently low, directly clarifying the scenario of replica symmetry breaking of DREM in the replica number space {\em without using the replica trick}. The validity of the expression is numerically confirmed.

Localization and freezing of a Gaussian chain in a quenched random potential.

The Gaussian chain in a quenched random potential (which is characterized by the disorder strength Delta) is investigated in the d-dimensional space by the replicated variational method. The general expression for the free energy within so-called one-step-replica symmetry breaking (1-RSB) scenario has been systematically derived. We have shown that the replica symmetrical (RS) limit of this expression can describe the chain center-of-mass localization and collapse. The critical disorder when the chain becomes localized scales as Delta(c) approximately b(d)N(-2+d/2) (where b is the length of the Kuhn segment length and N is the chain length) whereas the chain gyration radius R(g) approximately b(b(d)/Delta)(1/(4-d)). The freezing of the internal degrees of freedom follows to the 1-RSB-scenario and is characterized by the beads localization length D(2). It was demonstrated that the solution for D(2) appears as a metastable state at Delta=Delta(A) and behaves similarly to the corresponding frozen states in heteropolymers or in p-spin random spherical model.

Upper bounds on the mass of the lightest neutralino

AbstractWe derive the general upper bounds on the mass of the lightest neutralino, as afunction of the gluino mass, in different supersymmetry breaking models with minimalparticle content and the standard model gauge group. This includes models withgravity mediated supersymmetry breaking (SUGRA), as well as models with anomalymediated supersymmetry breaking (AMSB). We include the next-to-leading ordercorrections in our evaluation of these bounds. We then expand the mass matrix inpowers of M Z /µ, and find the upper bound on the mass of the lightest neutralinofrom this expansion. By scanning over all of the parameter space, we find that thebound we have obtained can be saturated. We compare the general upper bound onthe lightest neutralino mass to the upper bound that is obtained when the radiativeelectroweak symmetry breaking scenario is assumed. PACS number(s): 12.60.Jv, 14.80.Ly 1 Introduction It is widely expected that at least some supersymmetric particles will be produced at thelarge hadron collider (LHC) that is starting operation in a few years’ time. However,most of these supersymmetric particles will not be detected as such, since they will decayinto the particles of the Standard Model (SM), or to the lightest supersymmetric particle(LSP), which is stable as long as the R-parity is conserved. Thus, the experimental studyof supersymmetry involves the study of cascade decays of the supersymmetric particlesto the LSP and the reconstruction of the subsequent decay chains. The LSP in a largeclass of supersymmetry breaking models is the lightest neutralino, which has thus been asubject of intense study for a long time [1, 2, 3, 4, 5, 6]. A stable lightest neutralino is also1

A SUPERSYMMETRIC MODEL WITH THE GAUGE SYMMETRY SU(3)1 × SU(2)1 × U(1)1 × SU(3)2 × SU(2)2 × U(1)2

A supersymmetric model with two copies of the Standard Model gauge groups is constructed in the gauge mediated supersymmetry breaking scenario. The supersymmetry breaking messengers are in a simple form. The Standard Model is obtained after first step gauge symmetry breaking. In the case of one copy of the gauge interactions being strong, a scenario of electroweak symmetry breaking is discussed, and the gauginos are generally predicted to be heavier than the sfermions.

Pair production of charged Higgs scalars from electroweak gauge boson fusion

We compute the contribution to charged Higgs boson pair production at the large hadron collider (LHC) due to the scattering of two electroweak (EW) gauge bosons, these being in turn generated via bremsstrahlung of incoming quarks: qq → qqV*V* → qqH+H− (V = γ, Z, W±). We verify that the production cross section of this mode is tan β independent and show that it is smaller than that of H+H− production via qq-initiated processes, but generally larger than that of the loop-induced channel gg → H+H−. Pair production of charged Higgs bosons is crucial in order to test EW symmetry breaking scenarios beyond the standard model. We show that the detection of these kinds of processes at the standard LHC is, however, problematic, because of their poor production rates and large backgrounds.