Nishita Desai
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Previous Organizations / Institutes
The organizations / institutes from the scholar's other articles in the past ten years
Research Subjects
Nishita Desai has a total of 273 co-authors. Here are the top co-authors by number of shared publications:
- Jong Soo Kim
National Institute for Theoretical Physics and School of Physics, University of the Witwatersrand, Johannesburg, South Africa
5 shared publications - Krzysztof Rolbiecki
University of Warsaw
5 shared publications - Aoife Bharucha
Aix Marseille Univ Université de Toulon CNRS CPT Marseille France
4 shared publications - Biswarup Mukhopadhyaya
Regional Centre for Accelerator-based Particle Physics Harish-Chandra Research Institute HBNI Chhatnag Road 211019 Jhusi Allahabad India
4 shared publications - Robert Ziegler
Karlsruhe Institute of Technology (KIT)
4 shared publications - Andre Lessa
Universidade Federal do ABC
3 shared publications
Latest Publications
- Open Access
Axion-like particles as mediators for dark matter: beyond freeze-out
We consider an axion-like particle (ALP) coupled to Standard Model (SM) fermions as a mediator between the SM and a fermionic dark matter (DM) particle. We explore the case where the ALP-SM and/or the ALP-DM couplings are too small to allow for DM generation via standard freeze-out. DM is therefore thermally decoupled from the visible sector and must be generated through either freeze-in or decoupled freeze-out (DFO). In the DFO regime, we present an improved approach to obtain the relic density by solving a set of three stiff coupled Boltzmann equations, one of which describes the energy transfer from the SM to the dark sector. Having determined the region of parameter space where the correct relic density is obtained, we revisit experimental constraints from electron beam dump experiments, rare $B$ and $K$ decays, exotic Higgs decays at the LHC, astrophysics, dark matter searches and cosmology. In particular, for our specific ALP scenario we (re)calculate and improve beam dump, flavour and supernova constraints. Throughout our calculation we implement state-of-the-art chiral perturbation theory results for the ALP partial decay width to hadrons. We find that while the DFO region, which predicts extremely small ALP-fermion couplings, can probably only be constrained by cosmological observables, the freeze-in region covers a wide area of parameter space that may be accessible to other more direct probes. Some of this parameter space is already excluded, but a significant part should be accessible to future collider experiments.Open AccessAxion-like particles as mediators for dark matter: beyond freeze-out
We consider an axion-like particle (ALP) coupled to Standard Model (SM) fermions as a mediator between the SM and a fermionic dark matter (DM) particle. We explore the case where the ALP-SM and/or the ALP-DM couplings are too small to allow for DM generation via standard freeze-out. DM is therefore thermally decoupled from the visible sector and must be generated through either freeze-in or decoupled freeze-out (DFO). In the DFO regime, we present an improved approach to obtain the relic density by solving a set of three stiff coupled Boltzmann equations, one of which describes the energy transfer from the SM to the dark sector. Having determined the region of parameter space where the correct relic density is obtained, we revisit experimental constraints from electron beam dump experiments, rare $B$ and $K$ decays, exotic Higgs decays at the LHC, astrophysics, dark matter searches and cosmology. In particular, for our specific ALP scenario we (re)calculate and improve beam dump, flavour and supernova constraints. Throughout our calculation we implement state-of-the-art chiral perturbation theory results for the ALP partial decay width to hadrons. We find that while the DFO region, which predicts extremely small ALP-fermion couplings, can probably only be constrained by cosmological observables, the freeze-in region covers a wide area of parameter space that may be accessible to other more direct probes. Some of this parameter space is already excluded, but a significant part should be accessible to future collider experiments. - Open Access
- 16 June 2023
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2023 (6) , 1-22
Discovery prospects of a light charged Higgs near the fermiophobic region of Type-I 2HDM
Determining if the SM-like Higgs is part of an extended Higgs sector is the most important question to be asked after discovery. A light charged Higgs boson with mass smaller than the sum of top and bottom quarks is naturally allowed in Type-I two Higgs doublet model and can be produced in association with neutral scalars for large parts of parameter space at the LHC. Such low mass charged scalars typically have dominant decays to the fermionic modes viz. τν and cs. However in the presence of light neutral scalar (φ), the charged Higgs boson has a substantial branching fraction into the bosonic decay modes H±→ W(*)φ. Identifying the heavier neutral Higgs (H) with the observed 125 GeV Higgs and working in the limit $$ {M}_{H^{\pm }}\approx {M}_A $$ , we examine charged Higgs production and decay in the bosonic mode pp → H±h → W(∗)hh. The presence of two light Higgses (h) is then the key to identifying charged Higgs production. The light Higgs branching ratio is largely dominated by the $$ b\overline{b} $$ mode except when close to the fermiophobic limit. Here, the rates into $$ b\overline{b} $$ and γγ can be comparable and we can use the $$ \gamma \gamma b\overline{b} $$ signature. This signature is complementary to the hh → 4γ which has been previously discussed in literature. Using the lepton from the W boson, we demonstrate with a cut-and-count analysis that both the new light neutral Higgs as well as charged Higgs can be probed with reasonable significance at 13.6 TeV LHC with 300-3000 fb−1 of integrated luminosity.- 16 June 2023
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2023 (6) , 1-22
Open AccessDiscovery prospects of a light charged Higgs near the fermiophobic region of Type-I 2HDM
Determining if the SM-like Higgs is part of an extended Higgs sector is the most important question to be asked after discovery. A light charged Higgs boson with mass smaller than the sum of top and bottom quarks is naturally allowed in Type-I two Higgs doublet model and can be produced in association with neutral scalars for large parts of parameter space at the LHC. Such low mass charged scalars typically have dominant decays to the fermionic modes viz. τν and cs. However in the presence of light neutral scalar (φ), the charged Higgs boson has a substantial branching fraction into the bosonic decay modes H±→ W(*)φ. Identifying the heavier neutral Higgs (H) with the observed 125 GeV Higgs and working in the limit $$ {M}_{H^{\pm }}\approx {M}_A $$ , we examine charged Higgs production and decay in the bosonic mode pp → H±h → W(∗)hh. The presence of two light Higgses (h) is then the key to identifying charged Higgs production. The light Higgs branching ratio is largely dominated by the $$ b\overline{b} $$ mode except when close to the fermiophobic limit. Here, the rates into $$ b\overline{b} $$ and γγ can be comparable and we can use the $$ \gamma \gamma b\overline{b} $$ signature. This signature is complementary to the hh → 4γ which has been previously discussed in literature. Using the lepton from the W boson, we demonstrate with a cut-and-count analysis that both the new light neutral Higgs as well as charged Higgs can be probed with reasonable significance at 13.6 TeV LHC with 300-3000 fb−1 of integrated luminosity. - Open Access
- 14 February 2023
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2023 (2) , 1-61
Axion-like particles as mediators for dark matter: beyond freeze-out
We consider an axion-like particle (ALP) coupled to Standard Model (SM) fermions as a mediator between the SM and a fermionic dark matter (DM) particle. We explore the case where the ALP-SM and/or the ALP-DM couplings are too small to allow for DM generation via standard freeze-out. DM is therefore thermally decoupled from the visible sector and must be generated through either freeze-in or decoupled freeze-out (DFO). In the DFO regime, we present an improved approach to obtain the relic density by solving a set of three stiff coupled Boltzmann equations, one of which describes the energy transfer from the SM to the dark sector. Having determined the region of parameter space where the correct relic density is obtained, we revisit experimental constraints from electron beam dump experiments, rareBandKdecays, exotic Higgs decays at the LHC, astrophysics, dark matter searches and cosmology. In particular, for our specific ALP scenario we (re) calculate and improve beam dump, flavour and supernova constraints. Throughout our calculation we implement state-of-the-art chiral perturbation theory results for the ALP partial decay width to hadrons. We find that while the DFO region, which predicts extremely small ALP-fermion couplings, can probably only be constrained by cosmological observables, the freeze-in region covers a wide area of parameter space that may be accessible to other more direct probes. Some of this parameter space is already excluded, but a significant part should be accessible to future collider experiments.
- 14 February 2023
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2023 (2) , 1-61
Open AccessAxion-like particles as mediators for dark matter: beyond freeze-out
We consider an axion-like particle (ALP) coupled to Standard Model (SM) fermions as a mediator between the SM and a fermionic dark matter (DM) particle. We explore the case where the ALP-SM and/or the ALP-DM couplings are too small to allow for DM generation via standard freeze-out. DM is therefore thermally decoupled from the visible sector and must be generated through either freeze-in or decoupled freeze-out (DFO). In the DFO regime, we present an improved approach to obtain the relic density by solving a set of three stiff coupled Boltzmann equations, one of which describes the energy transfer from the SM to the dark sector. Having determined the region of parameter space where the correct relic density is obtained, we revisit experimental constraints from electron beam dump experiments, rareBandKdecays, exotic Higgs decays at the LHC, astrophysics, dark matter searches and cosmology. In particular, for our specific ALP scenario we (re) calculate and improve beam dump, flavour and supernova constraints. Throughout our calculation we implement state-of-the-art chiral perturbation theory results for the ALP partial decay width to hadrons. We find that while the DFO region, which predicts extremely small ALP-fermion couplings, can probably only be constrained by cosmological observables, the freeze-in region covers a wide area of parameter space that may be accessible to other more direct probes. Some of this parameter space is already excluded, but a significant part should be accessible to future collider experiments.
- Open Access
Status of leptoquark models after LHC Run-2 and discovery prospects at future colliders
We study limits from dilepton searches on leptoquark completions to the Standard Model in the parameter space motivated by anomalies in the $b \rightarrow s$ sector. After a full Run-2 analysis by LHCb, the disparity in lepton flavour violation has disappeared. However, the mismatch in angular distributions as well as in $B_s \rightarrow μ^+ μ^-$ partial width is still unresolved and still implies a possible new physics contribution. We probe three models of leptoquarks -- scalar models $S_3$ and $R_2$ as well as vector leptoquark model $U_1$ using non-resonant dilepton searches to place limit on both the mass and couplings to SM fermions. The exclusions of leptoquarks coupling either non-uniformly to different lepton flavours or uniformly is examined. Interestingly, if leptoquark couplings to electrons and muons are indeed universal, then the $U_1$ model parameter space that corresponds to the anomalous contribution should already accessible with Run-2 data in the non-resonant $eμ$ channel. In the non-universal case, there is a significant exclusion in couplings, but not enough to reach regions that explain observed anomalies. We, therefore, examine the prospective sensitivity at the HL-LHC as well as of a 3 TeV future muon collider. For the vector leptoquark model, we find that a muon collider can probe all of the relevant parameter space at 95% confidence with just 1 fb$^{-1}$ data whereas $R_2$ and $S_3$ models can be excluded at 95% with 5 fb$^{-1}$ and 6.5 fb$^{-1}$ luminosity respectively.Open AccessStatus of leptoquark models after LHC Run-2 and discovery prospects at future colliders
We study limits from dilepton searches on leptoquark completions to the Standard Model in the parameter space motivated by anomalies in the $b \rightarrow s$ sector. After a full Run-2 analysis by LHCb, the disparity in lepton flavour violation has disappeared. However, the mismatch in angular distributions as well as in $B_s \rightarrow μ^+ μ^-$ partial width is still unresolved and still implies a possible new physics contribution. We probe three models of leptoquarks -- scalar models $S_3$ and $R_2$ as well as vector leptoquark model $U_1$ using non-resonant dilepton searches to place limit on both the mass and couplings to SM fermions. The exclusions of leptoquarks coupling either non-uniformly to different lepton flavours or uniformly is examined. Interestingly, if leptoquark couplings to electrons and muons are indeed universal, then the $U_1$ model parameter space that corresponds to the anomalous contribution should already accessible with Run-2 data in the non-resonant $eμ$ channel. In the non-universal case, there is a significant exclusion in couplings, but not enough to reach regions that explain observed anomalies. We, therefore, examine the prospective sensitivity at the HL-LHC as well as of a 3 TeV future muon collider. For the vector leptoquark model, we find that a muon collider can probe all of the relevant parameter space at 95% confidence with just 1 fb$^{-1}$ data whereas $R_2$ and $S_3$ models can be excluded at 95% with 5 fb$^{-1}$ and 6.5 fb$^{-1}$ luminosity respectively. - Open Access
Discovery prospects of a light charged Higgs near the fermiophobic region of Type-I 2HDM
Determining if the SM-like Higgs is part of an extended Higgs sector is the most important question to be asked after discovery. A light charged Higgs boson with mass smaller than the sum of top and bottom quarks is naturally allowed in Type-I two Higgs doublet model and can be produced in association with neutral scalars for large parts of parameter space at the LHC. Such low mass charged scalars typically have dominant decays to the fermionic modes viz. $\tau\nu$ and $c s$. However in the presence of light neutral scalar ($\varphi$), the charged Higgs boson has a substantial branching fraction into the bosonic decay modes $H^{\pm} \to W^{(*)} \varphi$. Identifying the heavier neutral Higgs ($H$) with the observed 125 GeV Higgs and working in the limit $M_{H^\pm} \approx M_A$, we examine charged Higgs production and decay in the bosonic mode $p p \to H^\pm h \to W^{(*)}h h$. The presence of two light Higgses ($h$) is then the key to identifying charged Higgs production. The light Higgs branching ratio is largely dominated by the $b\bar{b}$ mode except when close to the fermiophobic limit. Here, the rates into $b \bar b$ and $\gamma \gamma$ can be comparable and we can use the $\gamma\gamma b\bar{b}$ signature. This signature is complementary to the $h h \to 4\gamma$ which has been previously discussed in literature. Using the lepton from the $W$ boson, we demonstrate with a cut-and-count analysis that both the new light neutral Higgs as well as charged Higgs can be probed with reasonable significance at 13.6 TeV LHC with 300-3000 fb$^{-1}$ of integrated luminosity.Open AccessDiscovery prospects of a light charged Higgs near the fermiophobic region of Type-I 2HDM
Determining if the SM-like Higgs is part of an extended Higgs sector is the most important question to be asked after discovery. A light charged Higgs boson with mass smaller than the sum of top and bottom quarks is naturally allowed in Type-I two Higgs doublet model and can be produced in association with neutral scalars for large parts of parameter space at the LHC. Such low mass charged scalars typically have dominant decays to the fermionic modes viz. $\tau\nu$ and $c s$. However in the presence of light neutral scalar ($\varphi$), the charged Higgs boson has a substantial branching fraction into the bosonic decay modes $H^{\pm} \to W^{(*)} \varphi$. Identifying the heavier neutral Higgs ($H$) with the observed 125 GeV Higgs and working in the limit $M_{H^\pm} \approx M_A$, we examine charged Higgs production and decay in the bosonic mode $p p \to H^\pm h \to W^{(*)}h h$. The presence of two light Higgses ($h$) is then the key to identifying charged Higgs production. The light Higgs branching ratio is largely dominated by the $b\bar{b}$ mode except when close to the fermiophobic limit. Here, the rates into $b \bar b$ and $\gamma \gamma$ can be comparable and we can use the $\gamma\gamma b\bar{b}$ signature. This signature is complementary to the $h h \to 4\gamma$ which has been previously discussed in literature. Using the lepton from the $W$ boson, we demonstrate with a cut-and-count analysis that both the new light neutral Higgs as well as charged Higgs can be probed with reasonable significance at 13.6 TeV LHC with 300-3000 fb$^{-1}$ of integrated luminosity. - Open Access
- 18 November 2022
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2022 (11) , 1-32
The charged Higgs from the Bottom-Up: probing flavor at the LHC
- 18 November 2022
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2022 (11) , 1-32
Open AccessThe charged Higgs from the Bottom-Up: probing flavor at the LHC
- Open Access
- 27 April 2022
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2022 (4) , 1-26
Frugal U(1)X models with non-minimal flavor violation for b → sℓℓ anomalies and neutrino mixing
We analyze the class of models with an extra U(1)X gauge symmetry that can account for the b → sℓℓ anomalies by modifying the Wilson coefficients C9e and C9μ of the operators $$ {O}_{9\mathrm{\ell}}\equiv \left(\overline{b}{\gamma}_{\mu }{P}_Ls\right)\left(\overline{\mathrm{\ell}}{\gamma}^{\mu}\mathrm{\ell}\right) $$ from their standard model values. At the same time, these models generate appropriate quark mixing, and give rise to neutrino mixing via the Type-I seesaw mechanism. Apart from the gauge boson Z′, these frugal models only have three right-handed neutrinos for the seesaw mechanism, an additional SU(2)L scalar doublet for quark mixing, and a SM-singlet scalar that breaks the U(1)X symmetry. This set-up identifies a class of leptonic symmetries, and necessitates non-zero but equal charges for the first two quark generations. If the quark mixing beyond the standard model were CKM-like, all these symmetries would be ruled out by the latest flavor constraints on Wilson coefficients and collider constraints on Z′ parameters. However, we identify a single-parameter source of non-minimal flavor violation that allows a wider class of U(1)X symmetries to be compatible with all data. We show that the viable leptonic symmetries have to be of the form Le± 3Lμ− Lτ or Le− 3Lμ + Lτ, and determine the (MZ′, gZ′) parameter space that may be probed by the high-luminosity data at the LHC.- 27 April 2022
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2022 (4) , 1-26
Open AccessFrugal U(1)X models with non-minimal flavor violation for b → sℓℓ anomalies and neutrino mixing
We analyze the class of models with an extra U(1)X gauge symmetry that can account for the b → sℓℓ anomalies by modifying the Wilson coefficients C9e and C9μ of the operators $$ {O}_{9\mathrm{\ell}}\equiv \left(\overline{b}{\gamma}_{\mu }{P}_Ls\right)\left(\overline{\mathrm{\ell}}{\gamma}^{\mu}\mathrm{\ell}\right) $$ from their standard model values. At the same time, these models generate appropriate quark mixing, and give rise to neutrino mixing via the Type-I seesaw mechanism. Apart from the gauge boson Z′, these frugal models only have three right-handed neutrinos for the seesaw mechanism, an additional SU(2)L scalar doublet for quark mixing, and a SM-singlet scalar that breaks the U(1)X symmetry. This set-up identifies a class of leptonic symmetries, and necessitates non-zero but equal charges for the first two quark generations. If the quark mixing beyond the standard model were CKM-like, all these symmetries would be ruled out by the latest flavor constraints on Wilson coefficients and collider constraints on Z′ parameters. However, we identify a single-parameter source of non-minimal flavor violation that allows a wider class of U(1)X symmetries to be compatible with all data. We show that the viable leptonic symmetries have to be of the form Le± 3Lμ− Lτ or Le− 3Lμ + Lτ, and determine the (MZ′, gZ′) parameter space that may be probed by the high-luminosity data at the LHC. - Open Access
Constraining electroweak and strongly charged long-lived particles with CheckMATE
Long-lived particles have become a new frontier in the exploration of physics beyond the Standard Model. In this paper, we present the implementation of four types of long-lived particle searches, viz. displaced leptons, disappearing track, displaced vertex (together with muons or with missing energy), and heavy charged tracks. These four categories cover the signatures of a large range of physics models. We illustrate their potential for exclusion and discuss their mutual overlaps in mass-lifetime space for two simple phenomenological models involving either a U(1)-charged or a coloured scalar.
Open AccessConstraining electroweak and strongly charged long-lived particles with CheckMATE
Long-lived particles have become a new frontier in the exploration of physics beyond the Standard Model. In this paper, we present the implementation of four types of long-lived particle searches, viz. displaced leptons, disappearing track, displaced vertex (together with muons or with missing energy), and heavy charged tracks. These four categories cover the signatures of a large range of physics models. We illustrate their potential for exclusion and discuss their mutual overlaps in mass-lifetime space for two simple phenomenological models involving either a U(1)-charged or a coloured scalar.
- Open Access
- 3 November 2021
- Published by Springer Nature in The European Physical Journal C
- Vol. 81 (11) , 1-19
Constraining electroweak and strongly charged long-lived particles with CheckMATE
Long-lived particles have become a new frontier in the exploration of physics beyond the Standard Model. In this paper, we present the implementation of four types of long-lived particle searches, viz. displaced leptons, disappearing track, displaced vertex with either muons or with missing transverse energy, and heavy charged tracks. These four categories cover the signatures of a large range of physics models. We illustrate their potential for exclusion and discuss their mutual overlaps in mass-lifetime space for two simple phenomenological models involving either a U(1)-charged or a coloured scalar.
- 3 November 2021
- Published by Springer Nature in The European Physical Journal C
- Vol. 81 (11) , 1-19
Open AccessConstraining electroweak and strongly charged long-lived particles with CheckMATE
Long-lived particles have become a new frontier in the exploration of physics beyond the Standard Model. In this paper, we present the implementation of four types of long-lived particle searches, viz. displaced leptons, disappearing track, displaced vertex with either muons or with missing transverse energy, and heavy charged tracks. These four categories cover the signatures of a large range of physics models. We illustrate their potential for exclusion and discuss their mutual overlaps in mass-lifetime space for two simple phenomenological models involving either a U(1)-charged or a coloured scalar.
- Open Access
Soft displaced leptons at the LHC
Soft displaced leptons are representative collider signatures of compressed dark sectors with feeble couplings to the standard model. Prime targets are dark matter scenarios where co-scattering or co-annihilation sets the relic abundance upon freeze-out. At the LHC, searches for soft displaced leptons are challenged by a large background from hadron or tau lepton decays. In this article, we present an analysis tailored for displaced leptons with a low transverse momentum threshold at 20 GeV. Using a neural network, we perform a comprehensive analysis of the event kinematics, including a study of the expected detection efficiencies and backgrounds at small momenta. Our results show that weak-scale particles decaying into soft leptons with decay lengths between 1mm and 1m can be probed with LHC Run 2 data. This motivates the need for dedicated triggers that maximize the sensitivity to displaced soft leptons.
Open AccessSoft displaced leptons at the LHC
Soft displaced leptons are representative collider signatures of compressed dark sectors with feeble couplings to the standard model. Prime targets are dark matter scenarios where co-scattering or co-annihilation sets the relic abundance upon freeze-out. At the LHC, searches for soft displaced leptons are challenged by a large background from hadron or tau lepton decays. In this article, we present an analysis tailored for displaced leptons with a low transverse momentum threshold at 20 GeV. Using a neural network, we perform a comprehensive analysis of the event kinematics, including a study of the expected detection efficiencies and backgrounds at small momenta. Our results show that weak-scale particles decaying into soft leptons with decay lengths between 1mm and 1m can be probed with LHC Run 2 data. This motivates the need for dedicated triggers that maximize the sensitivity to displaced soft leptons.