International Journal of Modern Physics A

High-energy collisions at the LHC are now starting. The new physics agenda of the LHC is reviewed, with emphasis on the hunt for the Higgs boson (or whatever replaces it) and supersymmetry. In particular, the prospects for discovering new physics in the 2010-2011 run are discussed.

Masses of heavy Standard Model (SM) fermions (top-quark, bottom-quark and tau-lepton) play an important role in the analysis of theories beyond the SM. They serve as low-energy input and reduce the parameter space of such theories. In this paper Minimal supersymmetric extension of the SM is considered and two-loop relations between known SM values of fermion masses and running parameters of the MSSM are studied within the effective theory approach. Both b-quark and τ-lepton have the same quantum numbers with respect to SU(2) group and in the MSSM acquire their masses due to interactions with the same Higgs doublet. As a consequence, for large values of tan β parameter corresponding Yukawa couplings also become large and together with tan β can significantly enhance radiative corrections. In the case of b-quark two-loop contribution to the relation between running bottom-quark mass in QCD and MSSM is known in literature. This paper is devoted to calculation of the NNLO corrections proportional to Yukawa couplings. For the τ-lepton obtained contribution can be considered as a good approximation to the full two-loop result. For the b-quark numerical analysis given in the paper shows that only the sum of strong and Yukawa corrections can play such a role.

A new method based on the Monte Carlo calculation on the lattice is proposed for studying the Casimir effect in noncompact lattice QED. As a test of our method, we have studied the standard Casimir problem for the two parallel plane surfaces (mirrors) with the oblique boundary conditions. Physically, these boundary conditions may appear in the problem of modeling the thin material film interactions, and can be generated by the additional Chern–Simons boundary term. This method of boundary condition generation is very suitable — due to its gauge invariance — for the lattice formulation of the Casimir problem.

In this paper, we calculate the coupling constants g_ϕa0γ and g_ϕσγ by utilizing ω–ϕ mixing scheme and taking into account the contributions of the three-particle twist-4 distribution amplitudes of the photon in the light-cone sum-rule approach. Our results: (1) 0.130 ≤ g_ϕa0γ ≤ 0.194 is in agreement with the previous estimations of these coupling constants which obtained from phenomenological considerations but less than the experimental value g_ϕa0γ = 1.64±0.05; (2) 0.055 ≤ g_ϕσγ ≤ 0.076 is consistent with the phenomenological value and the experimental value g_ϕσγ = 0.060±0.008.

We study the dynamics of a D3 brane in generic IIB warped compactifications, using the Hamiltonian formulation discussed in arXiv:0805.3700. Taking into account of both closed and open string fluctuations, we derive the warped Kähler potential governing the motion of a probe D3 brane. By including the backreaction of D3, we also comment on how the problem of defining a holomorphic gauge coupling on wrapped D7 branes in warped background can be resolved.

We present a novel solution to the low entropy and arrow of time puzzles of the initial state of the universe. Our approach derives from the physics of a specific generalization of Matrix theory put forth in earlier work as the basis for a quantum theory of gravity. The particular dynamical state space of this theory, the infinite-dimensional analogue of the Fubini–Study metric over a complex nonlinear Grassmannian, has recently been studied by Michor and Mumford. The geodesic distance between any two points on this space is zero. Here we show that this mathematical result translates to a description of a hot, zero entropy state and an arrow of time after the Big Bang. This is modeled as a far from equilibrium, large fluctuation driven, "freezing by heating" metastable ordered phase transition of a nonlinear dissipative dynamical system.

In this work, we have studied the Bianchi type-II anisotropic cosmological models in the theory based on Lyra's geometry in normal gauge in the presence and absence of the magnetic field. The physical and kinematical behaviors of the models have also been discussed.

We first give a proof that the supersymmetric configurations satisfy the equations of motion for type II supergravity. In flux compactifications, the string vacua preserving N = 2 supersymmetry are the twisted generalized Calabi–Yau manifold. The modulus space of the string vacua can be constructed. We discuss the generalized Dirac operator which adds a torsional term to the ordinary Dirac operator and compute its index by the path integral method. Via the variation of the action of supergravity one can introduce the generalized Ricci flow equations. We consider deforming the manifold with the generalized Ricci flow. Finally, we consider the linear stability of the fixed points of the generalized Ricci flow.

We calculate the emissivity due to neutrino-pair production in e⁺e^- annihilation in the context of a left–right symmetric model in a way that can be used in supernova calculations. We also present some simple estimates which show that such process can act as an efficient energy-loss mechanism in the shocked supernova core. We find that the emissivity is dependent on the mixing angle ϕ of the model in the allowed range for this parameter.

Ultra-High Energy Cosmic Rays (E ≥ 5 ×10¹⁹eV) are detected through Extensive Air Showers that are created when a primary cosmic ray particle interacts with the atmosphere of the Earth. The energy of the primary particle can be estimated experimentally based on simulations. In this paper we attempt to estimate the energy of UHECR hadrons (He, Li, C, Fe) by applying a Monte Carlo simulation code and we compare the results with the ones derived in our previous paper for proton initiated showers. The scenario of simulations is adapted to the P. Auger Observatory site.

Einstein's equation with a negative cosmological constant admit solutions which are asymptotically anti-de Sitter. We obtain Vaidya-like solutions to include both a null fluid and a string fluid in nonspherical (plane symmetric and cylindrical symmetric) anti-de Sitter space–times. Assuming that string fluid diffuse, we find analytical solutions to Einstein's field equations. Thus we extend the approach proposed by Glass and Krisch to nonspherical space–times with a negative cosmological constant. Some other exacts solutions are also presented and discussed.