arXiv subjects

Rahul Nigam

Publications and source records attributed to Rahul Nigam.

23 records · Page 2Linked to original sources

arXiv2017

Application of Association rule analysis to study the evolution of halos in Cosmological N-Body simulations

Merger trees track the evolution of halos across multiple snapshots. They assign for halos of a particular snapshot, the set of halos from previous snapshots they possibly originated from. In this work, Association rule analysis a well known technique from data mining has been used to build halo merger trees. Association rule analysis tries to find associations between different halos(in same as well as in snapshots) using the particle IDs of the particles which the halos are made of. Associations are expressed in the form of association rules. Merger trees are one of the several useful results one can obtain from the output of association rule analysis. Other results including halo substructure and halo splitting can also be extracted. Each type of output to be extracted from the association rule analysis output correspond to a pattern in association rules. Merger trees were formed and tested using the above technique. Dark matter simulations were run using Gadget-2 for 128^3 particles. Halos were extracted from the simulation snapshots using Amiga Halo Finder. Halo accretion history was plotted and compared against those formed using AHF merger tree builder.

astro-ph.IM↗

arXiv2008

Kinematical Analogy for Marginal Dyon Decay

We describe a kinematical analogy for the marginal decay of 1/4-BPS dyons in 4-dimensional N=4 string compactifications. In this analogy, the electric and magnetic charges play the role of spatial momenta, the BPS mass plays the role of energy, and 1/2-BPS dyons correspond to massless particles. Using SO(12,1) "Lorentz" invariance and standard kinematical formulae in particle physics, we provide simple derivations of the curves of marginal stability. We also show how these curves map into the momentum ellipsoid, and propose some applications of this analogy.

hep-th↗

arXiv2008

Constraints on "rare" dyon decays

We obtain the complete set of constraints on the moduli of N=4 superstring compactifications that permit "rare" marginal decays of 1/4-BPS dyons to take place. The constraints are analysed in some special cases. The analysis extends in a straightforward way to multi-particle decays. We discuss the possible relation between general multi-particle decays and multi-centred black holes.

hep-th↗

arXiv2007

Dyon Death Eaters

We study general two-body decays of primitive and non-primitive 1/4-BPS dyons in four-dimensional type IIB string compactifications. We find a ``master equation'' for marginal stability that generalises the curve found by Sen for half-BPS decay, and analyse this equation in a variety of cases including decays to 1/4-BPS products. For half-BPS decays, an interesting and useful relation is exhibited between walls of marginal stability and the mathematics of Farey sequences and Ford circles. We exhibit an example in which two curves of marginal stability intersect in the interior of moduli space.

hep-th↗

arXiv2007

Noncritical-Topological Correspondence: Disc Amplitudes and Noncompact Branes

We examine the duality between type 0 noncritical strings and topological B-model strings, with special emphasis on the flux dependence. The former theory is known to exhibit holomorphic factorisation upto a subtle flux-dependent disc term. We give a precise definition of the B-model dual and propose that it includes both compact and noncompact B-branes. The former give the factorised part of the free energy, while the latter violate holomorphic factorisation and contribute the desired disc term. These observations are generalised to rational radii, for which we derive a nonperturbatively exact result. We also show that our picture extends to a proposed alternative topological-anti-topological picture of the correspondence for type 0 strings.

hep-th↗