ANIRBAN KUNDU

Physics

I CHAKRABORTY

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Pramana - Journal of Physics

We consider the extension of the standard model by a complex scalar triplet field, which occurs naturally in several models of leptogenesis and the seesaw mechanism for neutrino mass generation, in the context of ameliorating the fine-tuning problem of the fundamental scalars through the Veltman condition, i.e. by demanding the sum of the quadratically divergent corrections to vanish (or be at a reasonable level) by virtue of some possible symmetry of the underlying theory. We show that it is possible to cancel all the scalar one-loop quadratic divergences, and hence obtain a viable solution for the fine-tuning problem, while satisfying the electroweak precision observables, including the ρ parameter, and successfully generating the neutrino masses. The stability of the scalar potential puts important constraints on the model. © 2014 American Physical Society.

Fulltext

Physical Review D - Particles, Fields, Gravitation and Cosmology

Triplet-extended scalar sector and the naturalness problem

The conjecture that some unknown symmetry is responsible for keeping the Higgs boson light at 125 GeV does not hold for the Standard Model, where the coefficient of the quadratic divergence of Higgs boson self-energy is far from zero. We show that such a cancellation can be achieved in two-Higgs doublet models, by virtue of which all the scalars remain at the electroweak scale and the naturalness problem is avoided. We explore the consequences of such cancellations in different two-Higgs doublet models with no flavor-changing neutral current, and show that the parameter space becomes tightly constrained; in particular, the ratio of two vacuum expectation values, tanβ, no longer remains a free parameter but turns out to be a function of the quartic couplings. © 2014 American Physical Society.

Two-Higgs doublet models confront the naturalness problem

Assuming that no other conventional new physics is found immediately at the LHC, we investigate how just the consistent solution of the scalar mass hierarchy problem points towards the minimal necessary field content. We show that to ameliorate the fine-tuning problem, one needs to introduce more scalar degrees of freedom. The simplest solution is one or more real singlets (with the possibility of combining two of them in a complex singlet), which may act as viable cold dark matter candidates, because the constraints on the scalar potential disfavor any mixing between the new scalar(s) with the SM doublet. Furthermore, the fine-tuning problem of the new scalars necessitates the introduction of vectorlike fermions. Thus, singlet scalar(s) and vector fermions are minimal enhancements over the Standard Model to alleviate the fine-tuning problem. We also show that the model predicts Landau poles for all the scalar couplings, whose positions depend only on the number of such singlets. Thus, introduction of some new physics at that scale becomes inevitable. We also discuss how the model confronts the LHC constraints and the latest XENON100 data. © 2013 American Physical Society.

Controlling the fine-tuning problem with singlet scalar dark matter

We consider an extension of the scalar sector of the Standard Model with a single complex Higgs triplet X. Such extensions are the most economic, model-independent way of generating neutrino masses through triplet interactions. We show that a term like a0ΦΦX† must be included in the most general potential of such a scenario in order to avoid a massless neutral physical scalar. We also demonstrate that a0 must be real, thus ruling out any additional source of CP violation. We then examine the implications of this term in the mass matrices of the singly and doubly charged scalar, neutral scalar and pseudoscalar fields. We find that, for small values of a0/v2, where v2 is the triplet vev, the spectrum allows the decay of heavier scalars into lighter ones via gauge interactions. For large a0/v2, the doubly charged, singly charged and neutral pseudoscalar bosons become practically degenerate, while the even-parity neutral scalars remain considerably lighter, thus emphasizing the possibility of decay of the singly charged or neutral pseudoscalar states into the neutral scalars. Constraints from the ρ-parameter are used to find nontrivial limits on the charged Higgs mass depending on a0. We also study the couplings of the various physical states in this scenario. For small values of |a0|/v2, we find the lightest neutral scalar field to be triplet dominated, and thus having extremely suppressed interactions with fermion as well as gauge-boson pairs. © 2009 IOP Publishing Ltd.

Journal	Pramana - Journal of Physics
Publisher	Indian Academy of Sciences
ISSN	0304-4289
Open Access	No