R S Sahu

Bio: R S Sahu is an academic researcher from University of Rajasthan. The author has contributed to research in topics: Physics. The author has an hindex of 1, co-authored 1 publications receiving 1 citations.

Low-mass doubly charged Higgs bosons at the LHC

Abstract: Search for light (within the mass range 84–200 GeV) doubly-charged Higgs bosons decaying into a pair of W-bosons has been deemed challenging using the conventional LHC searches with leptons, jets and missing transverse momentum in the final state. Such Higgses together with slightly heavier singly-charged and neutral Higgses, when arranged in an SU (2) L triplet as in the type-II see-saw model, are lately shown to accommodate the recent measurement of the W -boson mass by the CDF collaboration. These, when produced in a highly Lorentz-boosted regime, tend to manifest themselves as a single fat-jet or a pair of adjacent same-sign leptons plus missing transverse momentum. First, we perform a multivariate analysis to discern such exotic jets from the SM jets. Then, we present a novel search in the final state with an exotic jet and two same-sign leptons plus missing transverse momentum. We find that such low-mass doubly-charged Higgsses could be directly probed with the already collected Run 2 LHC data.

Evaluation of s, t, u parameters, triple gauge boson vertices and some oblique corrections in extra u(1) superstring inspired model

Abstract: Explicit evaluation of the following parameters has been carried out in the extraU (1) superstring inspired model: (i) As Mz2 varies from 555 GeV to 620 GeV and (m t) CDF = 175.6 ± 5.7 GeV (Table 1): (a) SNew varies from -0.100 ± 0.089 to -0.130 ± 0.090, (b) TNew varies from -0.098 ± 0.097 to -0.129 ± 0.098, (c) UNew varies from -0.229 ± 0.177 to -0.253 ± 0.206, (d) Τz varies from 2.487 ± 0.027 to 2.486 ± 0.027, (e) ALR varies from 0.0125 ± 0.0003 to 0.0126 ± 0.0003, (f) A FB b remains constant at 0.0080 ± 0.0007. Almost identical values are obtained for (m t)D0 = 169 GeV (see table 2). (ii) Triple gauge boson vertices (TGV) contributions: AsMz 2 varies from 555 GeV to 620 GeV and (m t) CDF = 175.6 ±5.7 GeV. (a)√s = 500 GeV, asymptotic case: $$\overline f _1^{Z_1 } $$ varies from -0.301 to -0.179; $$\overline f _{3|Z_1 }^{Z_1 } $$ varies from -0.622 to -0.379; $$f_5^{Z_1 } $$ varies from +0.0061 to 0.0056; $$\overline f _{3|Z_1 }^{\gamma _1 } $$ varies from -3.691 to -2.186. $$\overline f _z^{Z_2 } $$ varies from +0.270 to +0.118; $$\overline f _3^{Z_2 } $$ varies from +0.552 to 0.238; $$f_5^{Z_2 } $$ varies from +0.0004 to +0.0002; $$\overline f _{3|Z_2 }^{\gamma _1 } $$ remains constant at -0.110. (b)√s = 700 GeV, asymptotic case: $$\overline f _1^{Z_1 } $$ varies from -0.297 to -0.176; $$\overline f _3^{Z_1 } $$ varies from -0.609 to -0.370; $$\overline f _5^{Z_1 } $$ varies from -0.0082 to -0.0078; $$\overline f _{3|Z_1 }^{\gamma _1 } $$ varies from -3.680 to -2.171.√s = 700 GeV, nonasymptotic case: $$\overline f _1^{Z_2 } $$ varies from -0.173 to -0.299; $$\overline f _3^{Z_2 } $$ varies from-0.343 to -0.591; $$f_5^{Z_2 } $$ varies from -0.005 to -0.011; $$\overline f _{3|Z_2 }^{\gamma _1 } $$ remains constant at -0.110. The pattern of form factors values for√s = 1000, 1200 GeV is almost identical to that of√s= 700 GeV. Further the values of the form factors for (m t)D0 (=169 GeV) follow identical pattern as that of (m t) CDF form factors values (see tables 5, 6, 9, 10). We conclude that the values of all the form factors with the exception of these of $$f_5^{Z_1 } $$ , $$f_5^{Z_2 } $$ are comparable or larger than theS, T values and therefore the TGV contributions are important while deciding the use of extraU (1) model for doing physics beyond standard model.

Low energy theorems and the unitarity bounds in the extra U(1) superstring inspired E 6 models

Abstract: The conventional method using low energy theorems derived by Chanowitz et al. [Phys. Rev. Lett. 57, 2344 (1986);] does not seem to lead to an explicit unitarity limit in the scattering processes of longitudinally polarized gauge bosons for the high energy case in the extra U(1) superstring inspired models, commonly known as {eta} model, emanating from E{sub 6} group of superstring theory. We have made use of an alternative procedure given by Durand and Lopez [Phys. Lett. B 217, 463 (1989);], which is applicable to supersymmetric grand unified theories. Explicit unitarity bounds on the superpotential couplings (identified as Yukawa couplings) are obtained from both using unitarity constraints as well as using renormalization group equations (RGE) analysis at one-loop level utilizing critical couplings concepts implying divergence of scalar coupling at M{sub G}. These are found to be consistent with finiteness over the entire range M{sub Z}{<=}{radical}(s){<=}M{sub G} i.e. from grand unification scale to weak scale. For completeness, the similar approach has been made use of in other models i.e., {chi}, {psi}, and {nu} models emanating from E{sub 6} and it has been noticed that at weak scale, the unitarity bounds on Yukawa couplings do not differ among E{sub 6} extra U(1)more » models significantly except for the case of {chi} model in 16 representations. For the case of the E{sub 6}-{eta} model ({beta}{sub E} congruent with 9.64), the analysis using the unitarity constraints leads to the following bounds on various parameters: {lambda}{sub t(max.)}(M{sub Z})=1.294, {lambda}{sub b(max.)}(M{sub Z})=1.278, {lambda}{sub H(max.)}(M{sub Z})=0.955, {lambda}{sub D(max.)}(M{sub Z})=1.312. The analytical analysis of RGE at the one-loop level provides the following critical bounds on superpotential couplings: {lambda}{sub t,c}(M{sub Z}) congruent with 1.295, {lambda}{sub b,c}(M{sub Z}) congruent with 1.279, {lambda}{sub H,c}(M{sub Z}) congruent with 0.968, {lambda}{sub D,c}(M{sub Z}) congruent with 1.315. Thus superpotential coupling values obtained by both the approaches are in good agreement. Theoretically we have obtained bounds on physical mass parameters using the unitarity constrained superpotential couplings. The bounds are as follows: (i) Absolute upper bound on top quark mass m{sub t}{<=}225 GeV (ii) the upper bound on the lightest neutral Higgs boson mass at the tree level is m{sub H{sub 2}{sup 0}}{sup tree}{<=}169 GeV, and after the inclusion of the one-loop radiative correction it is m{sub H{sub 2}{sup 0}}{<=}229 GeV when {lambda}{sub t}{ne}{lambda}{sub b} at the grand unified theory scale. On the other hand, these are m{sub H{sub 2}{sup 0}}{sup tree}{<=}159 GeV, m{sub H{sub 2}{sup 0}}{<=}222 GeV, respectively, when {lambda}{sub t}={lambda}{sub b} at the grand unified theory scale. A plausible range on D-quark mass as a function of mass scale M{sub Z{sub 2}} is m{sub D}{approx_equal}O(3 TeV) for M{sub Z{sub 2}}{approx_equal}O(1 TeV) for the favored values of tan{beta}{<=}1. The bounds on aforesaid physical parameters in the case of {chi}, {psi}, and {nu} models in the 27 representation are almost identical with those of {eta} model and are consistent with the present day experimental precision measurements.« less

Probing compressed mass spectra in the type-II seesaw model at the LHC

Abstract: Despite a great deal of effort in searching for the triplet-like Higgses in the type-II seesaw model, evidence for their production is yet to be found at the LHC. As such, one might be in the balance regarding this model's relevance at the electroweak scale. In this work, we peruse a scenario, akin to compressed mass spectra in Supersymmetry, which might have eluded the experimental searches thus far. We perform a multivariate analysis to distinguish signals with a pair of same-sign leptons with low invariant mass from the SM processes, including those accruing from fake leptons and electron charge misidentification, and find that a significant part of the hitherto unconstrained parameter space could be probed with the already collected Run 2 13 TeV LHC and future HL-LHC data.

Type-II see-saw at $\mu^+$$\mu^-$ collider

Abstract: Doubly-charged Higgs bosons have extensively been searched at the LHC. In this work, we study the sensitivity reach of the doubly-charged scalar ($H^{\pm\pm}$) in muon collider for the well-known Type-II seesaw scenario. First, we perform a cut-based analysis to predict the discovery prospect in the muon collider operating with 3 TeV center of mass energy. In addition to this, we have also performed a multivariate analysis and compare the cut-based result with the result obtained from the multivariate analysis. We find that the cut-based analysis is more significant as compared to the multivariate analysis in the large doubly-charged scalar mass region. We predict that a doubly-charged scalar mass, $M_{H^{\pm\pm}}$, upto 1450 GeV can be probed with $5\sigma$ significance for center of mass $\sqrt{s}= 3$ TeV and integrated luminosity $\mathcal{L} = 1000\,\textrm{fb}^{-1}$.