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Debtosh Chowdhury

Publications and source records attributed to Debtosh Chowdhury.

31 records · Page 2Linked to original sources
arXiv2018

Constraints on dark matter annihilation to fermions and a photon

We consider Majorana dark matter annihilation to fermion - anti-fermion pair and a photon in the effective field theory paradigm, by introducing dimension 6 and dimension 8 operators in the Lagrangian. For a given value of the cut-off scale, the latter dominates the annihilation process for heavier dark matter masses. We find a cancellation in the dark matter annihilation to a fermion - anti-fermion pair when considering the interference of the dimension 6 and the dimension 8 operators. Constraints on the effective scale cut-off is derived while considering indirect detection experiments and the relic density requirements and they are compared to the bound coming from collider experiments.

hep-ph↗
arXiv2018

Update of Global Two-Higgs-Doublet Model Fits

We perform global fits of Two-Higgs-Doublet models with a softly broken $\mathbb{Z}_2$ symmetry to recent results from the LHC detectors CMS and ATLAS, that is signal strengths and direct search limits obtained at $\sqrt{s} = 8$ TeV and $\sqrt{s}=13$ TeV. We combine all available ATLAS and CMS constraints with the other relevant theoretical and experimental bounds and present the latest limits on the model parameters. We obtain that deviations from the so-called alignment limit $β-α=π/2$ cannot be larger than $0.03$ in type I and have to be smaller than $0.02$ in the remaining three types. For the latter, we also observe lower limits on the heavy Higgs masses in the global fit. The splittings between these masses cannot exceed $200$ GeV in the types I and X and $130$ GeV in the types II and Y. Finally, we find that the decay widths of the heavy Higgs particles cannot be larger than $7\%$ of their masses if they are lighter than $1.5$ TeV.

hep-ph↗
arXiv2017

Charge and Color Breaking Constraints in MSSM after the Higgs Discovery at LHC

We revisit the constraints on the parameter space of the Minimal Supersymmetric Standard Model (MSSM), from charge and color breaking minima in the light of information on the Higgs from the LHC so far. We study the behavior of the scalar potential keeping two light sfermion fields along with the Higgs in the pMSSM framework and analyze the stability of the vacuum. We find that for lightest stop $\lesssim 1$ TeV and small $μ\lesssim 500$ GeV, the absolute stability of the potential can be attained only for $|X_{t}| \lesssim \sqrt{ 6 m_{\tilde{t}_1} m_{\tilde{t}_2}}$. The bounds become stronger for larger values of the $μ$ parameter. Note that this is approximately the value of $X_t$ which maximizes the Higgs mass. Our bounds on the low scale MSSM parameters are more stringent than those reported earlier in literature. We reanalyze the stau sector as well, keeping both staus. We study the connections between the observed Higgs rates and vacuum (meta)stability. We show how a precision study of the ratio of signal strengths, ($μ_{γγ}/μ_{ZZ}$) can shed further light.

hep-ph↗
arXiv2016

Indirect Searches of the Degenerate MSSM

A degenerate sfermionic particle spectrum can escape constraints from flavor physics, and at the same time evade the limits from the direct searches if the degeneracy extends to the gaugino-higgsino sector. Inspired by this, we consider a scenario where all the soft terms have an approximately common mass scale at $M_{\text{SUSY}}$, with splittings $\lesssim \mathcal{O}(10\%)$. As a result, the third generation sfermions have large to maximal (left-right) mixing, the same being the case with charginos and some sectors of the neutralino mass matrix. We study this scenario in the light of discovery of the Higgs boson with mass $\sim$ 125 GeV. We consider constraints from $B$-physics, the anomalous magnetic moment of the muon and the dark matter relic density. We find that a supersymmetric spectrum as light as 600 GeV could be consistent with all current data and also account for the observed anomalous magnetic moment of the muon within $2σ$. The neutralino relic density is generally too small to saturate the measured cold dark matter relic density. Direct detection limits from XENON100 and LUX put severe constraints on this scenario which will be conclusively probed by XENONnT experiment.

hep-ph↗
arXiv2016

Next-to-leading order unitarity fits in Two-Higgs-Doublet models with soft $\mathbb{Z}_2$ breaking

We fit the next-to-leading order unitarity conditions to the Two-Higgs-Doublet model with a softly broken $\mathbb{Z}_2$ symmetry. In doing so, we alleviate the existing uncertainty on how to treat higher order corrections to quartic couplings of its Higgs potential. A simplified approach to implementing the next-to-leading order unitarity conditions is presented. These new bounds are then combined with all other relevant constraints, including the complete set of LHC Run I data. The upper $95\%$ bounds we find are $4.2$ on the absolute values of the quartic couplings, and $235$ GeV ($100$ GeV) for the mass degeneracies between the heavy Higgs particles in the type I (type II) scenario. In type II, we exclude an unbroken $\mathbb{Z}_2$ symmetry with a probability of $95\%$. All fits are performed using the open-source code HEPfit.

hep-ph↗
arXiv2015

Muon g-2 in Anomaly Mediated SUSY Breaking

Motivated by two experimental facts, the muon g-2 anomaly and the observed Higgs boson mass around 125 GeV, we propose a simple model of anomaly mediation, which can be seen as a generalization of mixed modulus-anomaly mediation. In our model, the discrepancy of the muon g-2 and the Higgs boson mass around 125 GeV are easily accommodated. The required mass splitting between the strongly and weakly interacting SUSY particles are naturally achieved by the contribution from anomaly mediation. This model is easily consistent with SU(5) or SO(10) grand unified theory.

hep-ph↗
arXiv2015

Same sign di-lepton candles of the composite gluons

Composite Higgs models, where the Higgs boson is identified with the pseudo-Nambu-Goldstone-Boson (pNGB) of a strong sector, typically have light composite fermions (top partners) to account for a light Higgs. This type of models generically also predicts the existence of heavy vector fields (composite gluons) which appear as an octet of QCD. These composite gluons generically become very broad resonances once phase-space allows them to decay into two composite fermions. This makes their traditional experimental searches, which are designed to look for narrow resonances, quite ineffective. In this paper we, as an alternative, propose to utilize the impact of composite gluons on the production of top partners to constrain their parameter space. We place constraints on the parameters of the composite resonances using the 8 TeV LHC data and also assess the reach of the 14 TeV LHC. We find that the high luminosity LHC will be able to probe composite gluon masses up to $\sim 6$ TeV, even in the broad resonance regime.

hep-ph↗
arXiv2015

Global fits of the two-loop renormalized Two-Higgs-Doublet model with soft $Z_2$ breaking

We determine the next-to-leading order renormalization group equations for the Two-Higgs-Doublet model with a softly broken $Z_2$ symmetry and CP conservation in the scalar potential. We use them to identify the parameter regions which are stable up to the Planck scale and find that in this case the quartic couplings of the Higgs potential cannot be larger than 1 in magnitude and that the absolute values of the S-matrix eigenvalues cannot exceed 2.5 at the electroweak symmetry breaking scale. Interpreting the 125 GeV resonance as the light CP-even Higgs eigenstate, we combine stability constraints, electroweak precision and flavour observables with the latest ATLAS and CMS data on Higgs signal strengths and heavy Higgs searches in global parameter fits to all four types of $Z_2$ symmetry. We quantify the maximal deviations from the alignment limit and find that in type II and Y the mass of the heavy CP-even (CP-odd) scalar cannot be smaller than 340 GeV (360 GeV). Also, we pinpoint the physical parameter regions compatible with a stable scalar potential up to the Planck scale. Motivated by the question how natural a Higgs mass of 125 GeV can be in the context of a Two-Higgs-Doublet model, we also address the hierarchy problem and find that the Two-Higgs-Doublet model does not offer a perturbative solution to it beyond 5 TeV.

hep-ph↗
arXiv2015

Explaining the Lepton Non-universality at the LHCb and CMS from a Unified Framework

The recent results from the LHCb in the context of $(B^+ \rightarrow K^+ l l)$ decay and the CMS analysis in the context of right handed $W$-boson ($W_R$) search show a $2.6σ$ and a $2.8σ$ deviations from the Standard Model expectations respectively. In this work, we address these two seemingly uncorrelated results in the context of \R-parity violating supersymmetry. We found that a particular combination of $LQD^c$-type operators which successfully explain the LHCb result, can also accommodate the CMS excess in the $eejj$ channel of the $W_R$ search.

hep-ph↗
arXiv2013

Revisiting lepton flavor violation in supersymmetric type II seesaw

In view of the recent measurement of reactor mixing angle $θ_{13}$ and updated limit on $BR(μ\to e γ)$ by the MEG experiment, we re-examine the charged lepton flavor violations in a framework of supersymmetric type II seesaw mechanism. Supersymmetric type II seesaw predicts strong correlation between $BR(μ\to e γ)$ and $BR(τ\to μγ)$ mainly in terms of the neutrino mixing angles. We show that such a correlation can be determined accurately after the measurement of $θ_{13}$. We compute different factors which can affect this correlation and show that the mSUGRA-like scenarios, in which slepton masses are taken to be universal at the high scale, predicts $3.5 \lesssim BR(τ\to μγ)/BR(μ\to e γ) \lesssim 30$ for normal hierarchical neutrino masses. Any experimental indication of deviation from this prediction would rule out the minimal models of supersymmetric type II seesaw. We show that the current MEG limit puts severe constraints on the light sparticle spectrum in mSUGRA model if the seesaw scale lies within $10^{13}$-$10^{15}$ GeV. It is shown that these constraints can be relaxed and relatively light sparticle spectrum can be obtained in a class of models in which the soft mass of triplet scalar is taken to be non-universal at the high scale.

hep-ph↗
arXiv2012

SUSEFLAV: program for supersymmetric mass spectra with seesaw mechanism and rare lepton flavor violating decays

Accurate supersymmetric spectra are required to confront data from direct and indirect searches of supersymmetry. \SUSEFLAV is a numerical tool which is capable of computing supersymmetric spectra accurately for various supersymmetric breaking scenarios applicable even in the presence of flavor violation. The program solves MSSM RGEs with complete $3\times3$ flavor mixing at 2-loop level and one loop finite threshold corrections to all MSSM parameters by incorporating radiative electroweak symmetry breaking conditions. The program also incorporates the Type-I seesaw mechanism with three massive right handed neutrinos at user defined mass scales and mixing. It also computes branching ratios of flavor violating processes such as $l_j \rightarrow l_iγ$, $l_j \rightarrow 3 ~l_i$, $b \rightarrow sγ$ and supersymmetric contributions to flavor conserving quantities such as $(g_μ-2)$. A large choice of executables suitable for various operations of the program are provided.

hep-ph↗
arXiv2010

Results from PAMELA, ATIC and FERMI : Pulsars or Dark Matter ?

It is well known that the dark matter dominates the dynamics of galaxies and clusters of galaxies. Its constituents remain a mystery despite an assiduous search for them over the past three decades. Recent results from the satellite-based PAMELA experiment detect an excess in the positron fraction at energies between 10-100 GeV in the secondary cosmic ray spectrum. Other experiments namely ATIC, HESS and FERMI show an excess in the total electron (\ps + \el) spectrum for energies greater 100 GeV. These excesses in the positron fraction as well as the electron spectrum could arise in local astrophysical processes like pulsars, or can be attributed to the annihilation of the dark matter particles. The second possibility gives clues to the possible candidates for the dark matter in galaxies and other astrophysical systems. In this article, we give a report of these exciting developments.

astro-ph.HE↗