I am interested in theoretical particle physics, in particular, in Higgs phenomenology, Dark Matter, Effective Field Theory, Neutrinos and physics related to Large Hadron Collider.
High energy astrophysical neutrinos interacting with ultralight dark matter (DM) can undergo flav... more High energy astrophysical neutrinos interacting with ultralight dark matter (DM) can undergo flavour oscillations that induce an energy dependence in the flavour ratios. Such a dependence on the neutrino energy will reflect in the track to shower ratio in neutrino telescopes like IceCube or KM3NeT. This opens up a possibility to study DM density profiles of astrophysical objects like AGN, GRB etc., which are the suspected sources of such neutrinos.
We find the constraints on various non-standard interactions (NSI) of neutrinos from monojet+&quo... more We find the constraints on various non-standard interactions (NSI) of neutrinos from monojet+"Image missing" T searches at the Large Hadron Collider (LHC). Also, we show that the measurement of neutrino-nucleon cross-section from the observation of high energy astrophysical neutrino events at IceCube facilitates strong constraints on NSI as well. To this end, we pursue a comparative study of the prospects of LHC and IceCube in detecting NSI, also mentioning the role of low-energy experiments. We discuss the case of NSI with a new vector boson Z′ and it is found that for some range of mz ′ LHC puts more stringent bound, whereas IceCube supersedes elsewhere. We also pay special attention to the case of Z′ of mass of a few GeVs, pointing out that the IceCube constraints can surpass those from LHC and low-energy experiments. Although, for contact-type effective interactions with two neutrinos and two partons, constraints from LHC are superior.
We explore the possibility that high energy astrophysical neutrinos can interact with the dark ma... more We explore the possibility that high energy astrophysical neutrinos can interact with the dark matter on their way to Earth. Keeping in mind that new physics might leave its signature at such energies, we have considered all possible topologies for effective interactions between neutrino and dark matter. Building models, that give rise to a significant flux suppression of astrophysical neutrinos at Earth, is rather difficult. We present a Z ′ -mediated model in this context. Encompassing a large variety of models, a wide range of dark matter masses from 10−21 eV up to a TeV, this study aims at highlighting the challenges one encounters in such a model building endeavour after satisfying various cosmological constraints, collider search limits and electroweak precision measurements.
We explore the possibility of the existence of excited leptons in the light of recent data on muo... more We explore the possibility of the existence of excited leptons in the light of recent data on muon $g - 2$ from BNL. We have been able to put stringent bounds on the relevant parameter space.
A method is presented using helicity cross sections for calculating neutrino-nucleon interactions... more A method is presented using helicity cross sections for calculating neutrino-nucleon interactions. The formalism is applied in the calculation of the pion spectra produced by nu_mu and nu_tau beams. The masses of the charged leptons are kept throughout the calculations. Cross sections are presented in numerous figures where the contributions of the significant form factors are also shown. The article
The leading order vacuum polarization contribution of very light millicharged fermions and scalar... more The leading order vacuum polarization contribution of very light millicharged fermions and scalar (spin-0) particles with charge \epsilon e and mass \mu to the Lamb shift of the hydrogen atom is shown to imply universal, i.e. \mu-independent, upper bounds on \epsilon: \epsilon \lsim 10^{-4} for \mu \lsim 1 keV in the case of fermions, and for scalars this bound is increased by a factor of 2. This is in contrast to expectations based on the commonly used approximation to the Uehling potential relevant only for conventionally large fermion (and scalar) masses.
In a two Higgs doublet model (2HDM), at the vicinity of the alignment limit, the extra contributi... more In a two Higgs doublet model (2HDM), at the vicinity of the alignment limit, the extra contributions to the couplings of the SM-like Higgs with other particles can be subdominant to the same coming from the six dimensional operators. In this context, we revisit the alignment limit itself. It is investigated to what extent these operators can mask the actual alignment in a 2HDM. The bosonic operators which rescale the Higgs kinetic terms can lead to substantial change in the parameter space of the model. We find that some other bosonic operators, which are severely constrained from the electroweak precision tests, can also modify the parameter space of 2HDM due to their anomalous momentum structures. A particular kind of Little Higgs model is explored as an example of 2HDM effective field theory in connection with 2HDM alignment. Choosing a suitable benchmark point in a Type-II 2HDM, we highlight the possibility that the exact alignment limit is ruled out at 95% CL in presence of such operators.
We present a complete (non-redundant) basis of CP-and flavour-conserving six-dimensional operator... more We present a complete (non-redundant) basis of CP-and flavour-conserving six-dimensional operators in a two Higgs doublet model (2HDM). We include Z 2-violating operators as well. In such a 2HDM effective field theory (2HDMEFT), we estimate how constraining the 2HDM parameter space from experiments can get disturbed due to these operators. Our basis is motivated by the strongly interacting light Higgs (SILH) basis used in the standard model effective field theory (SMEFT). We find out bounds on combinations of Wilson coefficients of such operators from precision observables, signal strengths of Higgs decaying into vector bosons etc. In 2HDMEFT, the 2HDM parameter space can play a significant role while deriving such constraints, by leading to reduced or even enhanced effects compared to SMEFT in certain processes. We also comment on the implications of the SILH suppressions in such considerations.
We investigate the status of models containing exotic fermions or extra Z-like neutral gauge boso... more We investigate the status of models containing exotic fermions or extra Z-like neutral gauge bosons in the light of the recent data on anomalous magnetic moment of muon. We find that it is possible to extract interesting bounds on the parameters characterizing such models. The bounds are particularly strong if the new flavour-changing neutral currents are axial vectorlike.
We study the CP even trilinear neutral gauge boson vertices at one-loop in the context of the Sta... more We study the CP even trilinear neutral gauge boson vertices at one-loop in the context of the Standard Model and the Minimal Supersymmetric Standard Model, assuming two of the vector bosons are on-shell. We also study the changes in the form-factors when these two bosons are off-shell.
If the neutrino mass is non-zero, as hinted by several experiments, then R-parity-violating super... more If the neutrino mass is non-zero, as hinted by several experiments, then R-parity-violating supersym-metric Yukawa couplings can drive a heavy neutrino decay into lighter states. The heavy neutrino may either decay radiatively into a lighter neutrino, or it may decay into three light neutrinos through a Z-mediated penguin. For a given mass of the decaying neutrino, we calculate its lifetime for the various modes, each mode requiring certain pairs of R-parity-violating couplings be non-zero. We then check whether the calculated lifetimes fall in zones allowed or excluded by cosmological requirements. For the latter case, we derive stringent new constraints on the corresponding products of R-parity-violating couplings for given values of the decaying neutrino mass. PACS number(s): 13.35.Hb, 12.60.Jv, 11.30.Fs
In this paper we study some of the low energy effects of a light stabilized radion field in the R... more In this paper we study some of the low energy effects of a light stabilized radion field in the Randall-Sundrum scenario. We find that the NLC 500 with its projected precision level will be able to probe the radion contribution to κ v and λ v for values of φ up to 500 Gev. On the other hand the BNL E821 experiment will be able to test the radion contribution to a µ for φ= 1 Tev and m φ ≤ m µ. We have also shown that the higgs-radion mixing induces a 2.6% correction in the WWh coupling. Finally by comparing the radionstralung process with the higgsstralung process we have found that the LEPI bound of 60 Gev on the higgs mass based on Z → hl ¯ l decay mode suggests a lower bound of about 35 Gev on the radion mass. PACS numbers: 11.10Kk, 04.50+h, 12.10 Dm.
High energy astrophysical neutrinos interacting with ultralight dark matter (DM) can undergo flav... more High energy astrophysical neutrinos interacting with ultralight dark matter (DM) can undergo flavour oscillations that induce an energy dependence in the flavour ratios. Such a dependence on the neutrino energy will reflect in the track to shower ratio in neutrino telescopes like IceCube or KM3NeT. This opens up a possibility to study DM density profiles of astrophysical objects like AGN, GRB etc., which are the suspected sources of such neutrinos.
We find the constraints on various non-standard interactions (NSI) of neutrinos from monojet+&quo... more We find the constraints on various non-standard interactions (NSI) of neutrinos from monojet+"Image missing" T searches at the Large Hadron Collider (LHC). Also, we show that the measurement of neutrino-nucleon cross-section from the observation of high energy astrophysical neutrino events at IceCube facilitates strong constraints on NSI as well. To this end, we pursue a comparative study of the prospects of LHC and IceCube in detecting NSI, also mentioning the role of low-energy experiments. We discuss the case of NSI with a new vector boson Z′ and it is found that for some range of mz ′ LHC puts more stringent bound, whereas IceCube supersedes elsewhere. We also pay special attention to the case of Z′ of mass of a few GeVs, pointing out that the IceCube constraints can surpass those from LHC and low-energy experiments. Although, for contact-type effective interactions with two neutrinos and two partons, constraints from LHC are superior.
We explore the possibility that high energy astrophysical neutrinos can interact with the dark ma... more We explore the possibility that high energy astrophysical neutrinos can interact with the dark matter on their way to Earth. Keeping in mind that new physics might leave its signature at such energies, we have considered all possible topologies for effective interactions between neutrino and dark matter. Building models, that give rise to a significant flux suppression of astrophysical neutrinos at Earth, is rather difficult. We present a Z ′ -mediated model in this context. Encompassing a large variety of models, a wide range of dark matter masses from 10−21 eV up to a TeV, this study aims at highlighting the challenges one encounters in such a model building endeavour after satisfying various cosmological constraints, collider search limits and electroweak precision measurements.
We explore the possibility of the existence of excited leptons in the light of recent data on muo... more We explore the possibility of the existence of excited leptons in the light of recent data on muon $g - 2$ from BNL. We have been able to put stringent bounds on the relevant parameter space.
A method is presented using helicity cross sections for calculating neutrino-nucleon interactions... more A method is presented using helicity cross sections for calculating neutrino-nucleon interactions. The formalism is applied in the calculation of the pion spectra produced by nu_mu and nu_tau beams. The masses of the charged leptons are kept throughout the calculations. Cross sections are presented in numerous figures where the contributions of the significant form factors are also shown. The article
The leading order vacuum polarization contribution of very light millicharged fermions and scalar... more The leading order vacuum polarization contribution of very light millicharged fermions and scalar (spin-0) particles with charge \epsilon e and mass \mu to the Lamb shift of the hydrogen atom is shown to imply universal, i.e. \mu-independent, upper bounds on \epsilon: \epsilon \lsim 10^{-4} for \mu \lsim 1 keV in the case of fermions, and for scalars this bound is increased by a factor of 2. This is in contrast to expectations based on the commonly used approximation to the Uehling potential relevant only for conventionally large fermion (and scalar) masses.
In a two Higgs doublet model (2HDM), at the vicinity of the alignment limit, the extra contributi... more In a two Higgs doublet model (2HDM), at the vicinity of the alignment limit, the extra contributions to the couplings of the SM-like Higgs with other particles can be subdominant to the same coming from the six dimensional operators. In this context, we revisit the alignment limit itself. It is investigated to what extent these operators can mask the actual alignment in a 2HDM. The bosonic operators which rescale the Higgs kinetic terms can lead to substantial change in the parameter space of the model. We find that some other bosonic operators, which are severely constrained from the electroweak precision tests, can also modify the parameter space of 2HDM due to their anomalous momentum structures. A particular kind of Little Higgs model is explored as an example of 2HDM effective field theory in connection with 2HDM alignment. Choosing a suitable benchmark point in a Type-II 2HDM, we highlight the possibility that the exact alignment limit is ruled out at 95% CL in presence of such operators.
We present a complete (non-redundant) basis of CP-and flavour-conserving six-dimensional operator... more We present a complete (non-redundant) basis of CP-and flavour-conserving six-dimensional operators in a two Higgs doublet model (2HDM). We include Z 2-violating operators as well. In such a 2HDM effective field theory (2HDMEFT), we estimate how constraining the 2HDM parameter space from experiments can get disturbed due to these operators. Our basis is motivated by the strongly interacting light Higgs (SILH) basis used in the standard model effective field theory (SMEFT). We find out bounds on combinations of Wilson coefficients of such operators from precision observables, signal strengths of Higgs decaying into vector bosons etc. In 2HDMEFT, the 2HDM parameter space can play a significant role while deriving such constraints, by leading to reduced or even enhanced effects compared to SMEFT in certain processes. We also comment on the implications of the SILH suppressions in such considerations.
We investigate the status of models containing exotic fermions or extra Z-like neutral gauge boso... more We investigate the status of models containing exotic fermions or extra Z-like neutral gauge bosons in the light of the recent data on anomalous magnetic moment of muon. We find that it is possible to extract interesting bounds on the parameters characterizing such models. The bounds are particularly strong if the new flavour-changing neutral currents are axial vectorlike.
We study the CP even trilinear neutral gauge boson vertices at one-loop in the context of the Sta... more We study the CP even trilinear neutral gauge boson vertices at one-loop in the context of the Standard Model and the Minimal Supersymmetric Standard Model, assuming two of the vector bosons are on-shell. We also study the changes in the form-factors when these two bosons are off-shell.
If the neutrino mass is non-zero, as hinted by several experiments, then R-parity-violating super... more If the neutrino mass is non-zero, as hinted by several experiments, then R-parity-violating supersym-metric Yukawa couplings can drive a heavy neutrino decay into lighter states. The heavy neutrino may either decay radiatively into a lighter neutrino, or it may decay into three light neutrinos through a Z-mediated penguin. For a given mass of the decaying neutrino, we calculate its lifetime for the various modes, each mode requiring certain pairs of R-parity-violating couplings be non-zero. We then check whether the calculated lifetimes fall in zones allowed or excluded by cosmological requirements. For the latter case, we derive stringent new constraints on the corresponding products of R-parity-violating couplings for given values of the decaying neutrino mass. PACS number(s): 13.35.Hb, 12.60.Jv, 11.30.Fs
In this paper we study some of the low energy effects of a light stabilized radion field in the R... more In this paper we study some of the low energy effects of a light stabilized radion field in the Randall-Sundrum scenario. We find that the NLC 500 with its projected precision level will be able to probe the radion contribution to κ v and λ v for values of φ up to 500 Gev. On the other hand the BNL E821 experiment will be able to test the radion contribution to a µ for φ= 1 Tev and m φ ≤ m µ. We have also shown that the higgs-radion mixing induces a 2.6% correction in the WWh coupling. Finally by comparing the radionstralung process with the higgsstralung process we have found that the LEPI bound of 60 Gev on the higgs mass based on Z → hl ¯ l decay mode suggests a lower bound of about 35 Gev on the radion mass. PACS numbers: 11.10Kk, 04.50+h, 12.10 Dm.
We revisit the multilepton (ml) + E / T signatures of the Inert Doublet Model of dark matter in f... more We revisit the multilepton (ml) + E / T signatures of the Inert Doublet Model of dark matter in future LHC experiments for m = 3,4 and simulate, for the first time, the m = 5 case. In addition to the usual constraints like unitarity, perturbativity, the precision electroweak data, the observed dark matter relic density of the Universe, we take into account the stringent constraints from the post Higgs (h) discovery era like the measured M h and the upper bound on the width of h decay which were not included in the earlier analyses. We find that the IDM model embedded in a grand dessert scenario so that the unitarity constraint holds up to a very high scale, the entire parameter space allowed by the above constraints can be probed by the LHC via the 3l for an integrated luminosity ∼ 3000 fb −1. On the other hand if any new physics shows up at a scale ∼ 10 TeV only a part of the enlarged allowed parameter space can be probed. The 4l and 5l signals can help to discriminate among different IDM scenarios as and when sufficient integrated luminosity accumulates.
We revisit the multilepton (ml) + E / T signatures of the Inert Doublet Model of dark matter in f... more We revisit the multilepton (ml) + E / T signatures of the Inert Doublet Model of dark matter in future LHC experiments for m = 3,4 and simulate, for the first time, the m = 5 case. In addition to the usual constraints like unitarity, perturbativity, the precision electroweak data, the observed dark matter relic density of the Universe, we take into account the stringent constraints from the post Higgs (h) discovery era like the measured M h and the upper bound on the width of h decay which were not included in the earlier analyses. We find that the IDM model embedded in a grand dessert scenario so that the unitarity constraint holds up to a very high scale, the entire parameter space allowed by the above constraints can be probed by the LHC via the 3l for an integrated luminosity ∼ 3000 fb −1. On the other hand if any new physics shows up at a scale ∼ 10 TeV only a part of the enlarged allowed parameter space can be probed. The 4l and 5l signals can help to discriminate among different IDM scenarios as and when sufficient integrated luminosity accumulates.
We explore the consequences of promoting bilinear R-parity violation, usually formulated in the m... more We explore the consequences of promoting bilinear R-parity violation, usually formulated in the minimal supersymmetric standard model framework, to a supersymmetric SU(5) grand unified theory. We observe that the limits on proton decay and neutrino mass place tight constraints on the bilinear SU(5) R-parity violating interactions of the colour triplet and SU(2) L doublet types respectively, creating a different doublet-triplet issue. The new mass-term-type parameters are both required to be small compared to the their expected order – the GUT scale. This cannot be resolved by an extension of the usual fine-tuning in the symmetry breaking scalar sector, which keeps the doublet sector light at the cost of pushing the triplet to the GUT-scale, and is an obstacle for R-parity violation in SU(5).
We show that the study of scalar resonances at various vector boson scattering processes at the L... more We show that the study of scalar resonances at various vector boson scattering processes at the Large Hadron Collider can serve as a useful tool to distinguish between different extensions of the scalar sector of the Standard Model. The recent measurement of the Higgs boson properties leaves enough room for the extended scalar sectors to be relevant for such studies. The shape of the resonances, being model dependent, can shed light on the viable parameter space of a number of theoretical models.
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Papers by Subhendu Rakshit