International Journal of Modern Physics A

We describe the design of the ATLAS and CMS detectors as they are being prepared to commence data-taking at CERN's Large Hadron Collider (LHC). The very high energy proton–proton collisions are meant to dissect matter and space–time itself into its primary elements and generators. The detectors by synthesizing the information from the debris of the collisions are reconstituting the interactions that took place. LHC's ATLAS and CMS experiments (and not only these) are at the closest point of answering in the lab some of the most puzzling fundamental observations in nature today.

The LHC (Large Hadron Collider) will be a top-quark factory. With 80 million pairs of top quarks and an additional 34 million single tops produced annually at the designed high luminosity, the properties of this particle will be studied to a great accuracy. The fact that the top quark is the heaviest elementary particle in the Standard Model with a mass right at the electroweak scale makes it tempting to contemplate its role in electroweak symmetry breaking, as well as its potential as a window to unknown new physics at the TeV scale. We summarize the expectations for top-quark physics at the LHC, and outline new physics scenarios in which the top quark is crucially involved.

Near-threshold production of neutral boson pairs is considered within the framework of the model of unstable particles with smeared mass. The results of calculations are in good agreement with LEP II data and Monte Carlo simulations. Suggested approach significantly simplifies calculations with respect to standard perturbative one.

The old cosmological constant problem can be solved once we require that the full standard Einstein–Hilbert Lagrangian, gravity plus matter, is multiplied by a total derivative. We analyze such a picture writing the total derivative as the covariant gradient of a new vector field (b_μ). Like in unimodular gravity, integration constants, regenerating an effective cosmological constant, can reenter into the game depending on the dynamics of the b_μ field. In order to fit the present universe status without fine-tunings, a full understanding of the scales related to b_μ field dynamics has to be settled down.

We propose a method to treat the three-gluon self-interaction vertex in the position space in D = 4 - 2∊ dimensions. As an example, we calculate a two-loop contribution to auxiliary Lcc vertex in the Landau gauge which contains the three-gluon vertex for SU(N) Yang–Mills theory. We represent the integral expression as a sum of separate contributions so that each of the contributions is a double finite integral or single integral (singular or finite) in the position space. In each double finite integral, we use the freedom to shift exponents in powers in the denominator of integrands by some multiples of ∊, in order to perform at least one of the integrations by the uniqueness technique without corrupting the first term of the decomposition in ∊.

The recent experimental results on the spectrum of highly excited light nonstrange mesons are known to reveal a high degree of degeneracy among different groups of states. We revise some suggestions about the nature of the phenomenon and put the relevant ideas into the final shape. The full group of approximate mass degeneracies is argued to be SU(2)_f × I × O(4), where I is the degeneracy of isosinglets and isotriplets and O(4) is the degeneracy group of the relativistic hydrogen atom. We discuss the dynamical origin and consequences of considered symmetry with a special emphasis on distinctions of this symmetry from the so-called chiral symmetry restoration scenario.

We construct actions of Green–Schwarz sigma models on supercoset targets with ℤ_4m grading whose kinetic terms only contain the target-space bosons. We consider a simple case of such kinetic term and show that there exist a one-parameter family of flat currents of the model by requiring a suitable choice of the Wess–Zumino term. Such flat currents naturally lead to a hierarchy of classical conserved nonlocal charges. We also find that the one-parameter flat currents of the model satisfy equations of motion and the Virasoro constraint. This implies that one can generate a series of classical solutions from an existing one. When m = 1, our model coincides with the well-known model given by Metsaev and Tseytlin on a supercoset PSU(2, 2|4)/[SO(4, 1) × SO(5)] and similar models.

We obtain the analog of collapsing Vaidya-like solution to include both a null fluid and a string fluid, with a linear equation of state (p_⊥ = kρ), in nonspherical (plane symmetric and cylindrically symmetric) anti-de Sitter space–times. It turns out that the nonspherical collapse of two fluid in anti-de Sitter space–times, in accordance with cosmic censorship, proceed to form black holes, i.e. on naked singularity ever forms, in accordance with cosmic censorship, violating hoop conjecture.