International Journal of Modern Physics A

The Large Hadron Collider (LHC) was first suggested (in a documented way) in 1983 (S. Myers and W. Schnell, Preliminary performance estimates for a LEP proton collider, LEP Note 440, April 1983) as a possible future hadron collider to be installed in the 27 km "LEP" tunnel. More than 30 years later the collider has been operated successfully with beam for three years with spectacular performance and has discovered the long-sought-after Higgs boson. The LHC is the world's largest and most energetic particle collider. It took many years to plan and build this large complex machine which promises exciting, new physics results for many years to come.

I describe the LHC design objectives, review some of the more relevant beam effects, define the major accelerator components and parameters, and finally give an overview of the commissioning and operational performance since the initial turn on of the collider. The latter will include the major accident which took place in September 2008 and the subsequent repair and redesign of the faulty components.

The first attempt to circulate beam in the LHC in September 2008 were initially very successful. However, after only nine days of preliminary beam commissioning, on 19 September 2008, disaster struck: the last octant was being ramped up in preparation for high energy operation when a magnet interconnect failed and the enormous energy stored in the superconducting magnets was released in an uncontrolled way and damaged around 600 m of the LHC installed equipment. The next 14 months were crucial for the machine. A crash programme for the repair of the damaged sector was initiated as well as in depth studies to understand the cause of the failure and make design changes which would ensure that such an accident could never reoccur in the future.

In this paper, the story of the four years of the intensive activity since the accident is described starting with the repair of the damaged area and followed by the three very successful years of beam operation.

Large Hadron Collider forward (LHCf) has successfully completed the operation during the LHC 2009–2010 period and the detectors were removed in July 2010. The event trigger, data analysis and background have been intensively studied in order to derive inclusive single photon and π⁰ spectra. In this paper, the details of these intensive studies are described.

The first part is an introductory description of a small cross-section of the literature on algebraic methods in nonperturbative quantum gravity with a specific focus on viewing algebra as a laboratory in which to deepen understanding of the nature of geometry. This helps to set the context for the second part, in which we describe a new algebraic characterization of the Dirac operator in noncommutative geometry and then use it in a calculation on the form of the fermion mass matrix. Assimilating and building on the various ideas described in the first part, the final part consists of an outline of a speculative perspective on (noncommutative) quantum spectral gravity. This is the second of a pair of papers so far on this project.

Quasiparticle quark–gluon plasma (qQGP) model and strongly coupled quark–gluon plasma (SCQGP) are two different phenomenological models of quark–gluon plasma (QGP) that try to explain the nonideal behavior seen in lattice simulation of QCD and in relativistic heavy ion collisions. These models almost successfully explain the existing lattice data up to 5T_c. Here, we investigate how better these models fit the recent lattice data results of precision SU(3) thermodynamics for a large temperature range (up to 1000T_c) by studying the statistical mechanics and thermodynamics of gluon plasma and hence we have a complete phenomenological description of the equation of state of QGP from the phase transition through the perturbative region up to Stefan–Boltzmann limit. We also study the effect of orders of running coupling constants on the models and used the equation of state obtained using these models in predicting behavior of quantity like velocity of sound in high temperature, which has no lattice QCD results for such high temperatures.

The nilpotent Becchi–Rouet–Stora–Tyutin (BRST), anti-BRST, dual-BRST and anti-dual-BRST symmetry transformations are constructed in the context of noncommutative (NC) 1-form as well as 2-form gauge theories. The corresponding Noether's charges for these symmetries on the Moyal plane are shown to satisfy the same algebra, as by the de Rham cohomological operators of differential geometry. The Hodge decomposition theorem on compact manifold is also studied. We show that noncommutative gauge theories are field theoretic models for Hodge theory.

We have addressed the issue of field redefinition in connection with renormalizability. Our study is restricted to theories of interacting scalar fields. We have, in particular, shown that if a theory is renormalizable in the usual power-counting sense then it remains renormalizable in the same sense after a change of variables. This is due to the use of the powerful method of the background field expansion. In the case of a single complex scalar field, it turns out that the determination of the counterterms is much simpler when polar coordinates are used. We illustrate this by carrying out a one-loop calculation in the latter case.

Many extensions to the Standard Model imply the existence of new charged scalar Higgs bosons. We study the contribution of a general scalar or pseudoscalar coupling for the neutrino–electron scattering. We take a phenomenological approach in order to obtain model independent limits to the couplings that arise in this picture. We illustrate the reach of the constraints by studying the particular case of the type III two Higgs doublet model, where we have found new constraints to some elements of the Yukawa couplings mixing matrix (|Y_ee| ≤ 1 × 10^-1 and |Y_eμ| ≤ 7 × 10^-2 at 90% CL).

Solutions of geodesic equations describing propagation of gravitons in the bulk are studied in a cosmological model with one extra dimension. Brane with matter is embedded in the bulk. It is shown that in the period of early cosmology gravitons emitted from the brane to the bulk under certain conditions can return back to the brane. The model is discussed in two alternative approaches: (i) brane with static metric moving in the AdS space, and (ii) brane located at a fixed position in extra dimension with nonstatic metric. Transformation of coordinates from the one picture to another is performed. In both approaches, conditions for gravitons emitted to the bulk to come back to the brane are found.