arXiv subjects

Po-Yan Tseng

Publications and source records attributed to Po-Yan Tseng.

At least 55 records · Page 3Linked to original sources

arXiv2016

Probing a dark photon using rare leptonic kaon and pion decays

Rare leptonic kaon and pion decays $K^+(π^+) \to μ^+\, ν_μ\, e^+ e^-$ can be used to probe a dark photon of mass ${\cal O}(10)$~MeV, with the background coming from the mediation of a virtual photon. This is most relevant for the 16.7-MeV dark photon proposed to explain a 6.8$σ$ anomaly recently observed in $^8$Be transitions by the Atomki Collaboration. We evaluate the reach of future experiments for different scenarios of how the dark photon couples with the standard model particles, and show that a great portion of the preferred 16.7-MeV dark photon parameter space can be decisively probed. We also show the use of angular distributions to further distinguish the signal from the background.

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arXiv2016

Double Higgcision: 125 GeV Higgs boson and a potential diphoton Resonance

Searches for diphoton resonance have been shown to be very useful in discovering new heavy spin-0 or spin-2 particles. Supposing that a new heavy particle shows up in the diphoton channel and it points to a spin-0 boson, it can be allowed to have a small mixing with the observed 125 GeV Higgs-like boson. We borrow the example of the 750 GeV particles hinted with 3.2 fb$^{-1}$ data at the end of 2015 (though it did not appear in the 2016 data) to perform an analysis of "double Higgcision". In this work, we perform a complete Higgs-signal strength analysis in the Higgs-portal type framework, using all the existing 125 GeV Higgs boson data as well as the diphoton signal strength of the 750 GeV scalar boson. The best fit prefers a very tiny mixing between two scalar bosons, which has to be accommodated in models for the 750 GeV scalar boson.

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arXiv2016

Higgs precision study of the 750 GeV diphoton resonance and the 125 GeV standard model Higgs boson with Higgs-singlet mixing

We interpret the potential observation of the 750 GeV di-photon resonance at the LHC in models, in which an $SU(2)$ isospin-singlet scalar boson mixes with the Standard Model (SM) Higgs boson through an angle $α$. Allowing the singlet scalar boson to have renormalizable couplings to vector-like leptons and quarks and introducing sizable decay width of the 750 GeV di-photon resonance into non-SM particles such as dark matters, we can explain the large production cross section $σ(H_2) \times B(H_2 \to γγ)$ as well as the apparent large total width of the boson without conflicts from the results obtained by previous global fits to the SM Higgs boson data.

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arXiv2016

Resurgence of $Z'$ from the single electron-muon event at ATLAS

Inspired by the recent single $e^{\pm}μ^{\mp}$ event at 2.1 TeV invariant mass from the ATLAS at $\sqrt{s}=13$ TeV with 3.2 fb$^{-1}$ luminosity, we propose an explanation using a $Z'$ gauge boson, which possesses lepton-flavor-changing neutral currents originated from non-universal couplings to charged leptons. We assume that the left-handed charged-lepton mixing matrix equals to the PMNS matrix and no mixing in the neutrino sector to make this phenomenological $Z'$ model more predictive. There are indeed some parameter regions, where the $Z'$ can generate a large enough $e^{\pm}μ^{\mp}$ production cross section, while at the same time satisfies various observables from lepton-flavor violation and other constraints from the LHC.

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arXiv2016

Dark Matter with multi-annihilation channels and AMS-02 positron excess and antiproton

AMS-02 provided the unprecedented statistics in the measurement of the positron fraction from cosmic rays. That may offer a unique opportunity to distinguish the positron spectrum coming from various dark matter (DM) annihilation channels, if DM is the source of this positron excess. Therefore, we consider the scenario that the DM can annihilate into leptonic, quark, and massive gauge boson channels simultaneously with floating branching ratios to test this hypothesis. We also study the impacts from MAX, MED, MIN, and DC diffusion models as well as from isothermal, NFW, and Einasto DM density profiles on our results. We found two parameter regions that can satisfy both AMS-02 $\frac{e^+}{e^++e^-}$ and $\bar{p}/p$ datasets at 95\% CL. i) Under the NFW-MIN combination with $M_χ\subset[10,30]$ TeV. ii) Under the Einasto-DC combination with $M_χ\subset[500,1500]$ GeV.

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arXiv2015

Interpretations of the ATLAS Diboson Anomaly

Recently, the ATLAS Collaboration recorded an interesting anomaly in diboson production with excesses at the diboson invariant mass around 2 TeV in boosted jets of all the $WZ$, $W^+ W^-$, and $ZZ$ channels. We offer a theoretical interpretation of the anomaly using a phenomenological right-handed model with extra $W'$ and $Z'$ bosons. Constraints from narrow total decay widths, dijet cross sections, and $W/Z + H$ production are taken into account. We also comment on a few other possibilities.

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arXiv2015

Bounds on Higgs-Portal models from the LHC Higgs data

In a number of Higgs-portal models, an $SU(2)$ isospin-singlet scalar boson generically appears at the electroweak scale and can mix with the Standard Model (SM) Higgs boson with a mixing angle $α$. This singlet scalar boson can have renormalizable couplings to a pair of dark matter particles, vectorlike leptons or quarks, or new gauge bosons, thereby modifying the Higgs signal strengths in a nontrivial way. In this work, we perform global fits to such models using the most updated LHC Higgs-boson data and discuss the corresponding implications on Higgs-portal-type models. In particular we find that the current LHC Higgs-boson data slightly favors the SM over the Higgs-portal singlet-scalar models, which has to be further examined using the upcoming LHC Higgs-boson data. Finally the Higgs-portal models are constrained as follows: $\cosα\gtrsim 0.86$ and $ΔΓ_{\rm tot} \lesssim 1.9$ MeV at 95 \% CL.

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arXiv2015

Higgs data constraints on the minimal supersymmetric standard model

We perform global fits to the most recent data (after summer 2014) on Higgs boson signal strengths in the framework of the minimal supersymmetric standard model (MSSM). We further impose the existing limits on the masses of charginos, staus, stops and sbottoms together with the current Higgs mass constraint $|M_{H_1} - 125.5\,{\rm GeV}| < 6$ GeV. The heavy supersymmetric (SUSY) particles such as squarks enter into the loop factors of the $Hgg$ and $Hγγ$ vertices while other SUSY particles such as sleptons and charginos also enter into that of the $Hγγ$ vertex. We also take into account the possibility of other light particles such as other Higgs bosons and neutralinos, such that the 125.5 GeV Higgs boson can decay into. We use the data from the ATLAS, CMS, and the Tevatron, with existing limits on SUSY particles, to constrain on the relevant SUSY parameters. We obtain allowed regions in the SUSY parameter space of squark, slepton and chargino masses, and the $μ$ parameter. We find that $|ΔS^γ/S^γ_{\rm SM}|\lsim 0.1$ at $68\%$ confidence level when $M_{\tildeχ^{\pm}_1}>300$ GeV and $M_{\tildeτ_1}>300$ GeV, irrespective of the squarks masses. Furthermore, $|ΔS^γ/S^γ_{\rm SM}|\lsim 0.03 $ when $M_{\tildeχ^\pm_1,{\tildeτ_1}} > 500$ GeV and $M_{{\tilde t}_1,{\tilde b}_1} \gsim 600$ GeV.

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arXiv2015

Leptoquark induced rare decay amplitudes $h \to τ^\mp μ^\pm$ and $τ\to μγ$

Rare decay modes of the newly discovered standard-model-like Higgs boson $h$ may test the flavor changing couplings in the leptoquark sector through the process $h \to τ^\mpμ^\pm$. Motived by the recently reported excess in LHC data from the CMS detector, we found that a predicted branching fraction Br($h \to τ^\mpμ^\pm$) at the level of 1\% is possible even though the coupling parameters are subjected to the stringent constraint from the null observation of $τ\toμγ$, where the destructive cancellation among amplitudes is achievable by fine tuning.

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arXiv2014

Higgcision Updates 2014

During the 2014 Summer Conferences, both ATLAS and CMS Collaborations of the LHC experiments have demonstrated tremendous efforts in treatment of data and processing more data such that most data on signal strengths have improved; especially the diphoton and fermionic modes of both experiments. Here in this note we perform an update to our previous model-independent Higgs precision analysis -- Higgcision. We found the followings: (i) the uncertainties on most couplings shrink about 10--20%, (ii) the nonstandard (e.g. invisible) decay branching ratio of the Higgs boson is constrained to be less than 19% if only the width is allowed to vary, (iii) the gauge-Higgs coupling C_v is constrained to be 0.94 +0.11 -0.12, in which the uncertainty is reduced by about 10%, and (iv) the standard model (SM) Higgs boson still provides the best fit to all the Higgs boson data, and compared to the previous results the SM Higgs boson now enjoys a higher p value than the last year.

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arXiv2014

Confronting Higgcision with Electric Dipole Moments

Current data on the signal strengths and angular spectrum of the 125.5 GeV Higgs boson still allow a CP-mixed state, namely, the pseudoscalar coupling to the top quark can be as sizable as the scalar coupling: $C_u^S \approx C_u^P =1/2$. CP violation can then arise and manifest in sizable electric dipole moments (EDMs). In the framework of two-Higgs-doublet models, we not only update the Higgs precision (Higgcision) study on the couplings with the most updated Higgs signal strength data, but also compute all the Higgs-mediated contributions from the 125.5 GeV Higgs boson to the EDMs, and confront the allowed parameter space against the existing constraints from the EDM measurements of Thallium, neutron, Mercury, and Thorium monoxide. We found that the combined EDM constraints restrict the pseudoscalar coupling to be less than about $10^{-2}$, unless there are contributions from other Higgs bosons, supersymmetric particles, or other exotic particles that delicately cancel the current Higgs-mediated contributions.

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arXiv2013

Higgcision in the Two-Higgs Doublet Models

We perform global fits to general two-Higgs doublet models (2HDMs) with generalized couplings using the most updated data from ATLAS, CMS, and Tevatron. We include both scenarios with CP-conserving and CP-violating couplings. By relaxing the requirement on the discrete symmetries that are often imposed on the Yukawa couplings, we try to see which of the 2HDMs is preferred. We found that (i) Higgcision in 2HDMs can be performed efficiently by using only 4 parameters including the charged Higgs contributions to the Higgs couplings to two photons, (ii) the differences among various types of 2HDMs are very small with respect to the chi-square fits, (iii) $\tanβ$ is constrained to be small, (iv) the $p$-values for various fits in 2HDMs are worse than that of the standard model. Finally, we put emphasis on our findings that future precision measurements of the Higgs coupling to the scalar top-quark bilinear ($C_u^S$) and $\tanβ$ may endow us with the discriminating power among various types of 2HDMs especially when $C_u^S$ deviates from its SM value 1.

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arXiv2013

Collider Constraints on the Dark Matter Interpretation of the CDMS II Results

The recent observation of three events by the CDMS II experiment can be interpreted as a 8.6 GeV dark matter scatters elastically with the nucleons inside the silicon detectors with a spin-independent cross section of 1.9 x 10^-41 cm^2. We employ the effective dark matter interaction approach to fit to the interpreted cross section, and make predictions for monojet and monophoton production at the LHC with the fitted parameters. We show that some of the operators are already ruled out by current data while the others can be further probed in the upcoming 14 TeV run of the LHC.

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arXiv2013

Higgs Precision (Higgcision) Era begins

After the discovery of the Higgs boson at the LHC, it is natural to start the research program on the precision study of the Higgs-boson couplings to various standard model (SM) particles. We provide a generic framework for the deviations of the couplings from their SM values by introducing a number of parameters. We show that a large number of models beyond the SM can be covered, including two-Higgs-doublet models, supersymmetric models, little-Higgs models, extended Higgs sectors with singlets, and fourth generation models. We perform global fits to the most updated data from CMS, ATLAS, and Tevatron under various initial conditions of the parameter set. In particular, we have made explicit comparisons between the fitting results BEFORE and AFTER the Moriond 2013 meetings. Highlights of the results include: (i) the nonstandard decay branching ratio of the Higgs boson is less than 22%; (ii) the most efficient way to achieve the best fit for the data before the Moriond update is to introduce additional particle contributions to the triangular-loop functions of Hγγand Hgg vertices; (iii) the 1σallowed range of the relative coupling of HVV is 1.01 +0.13 -0.14, which means that the electroweak-symmetry breaking contribution from the observed Higgs boson leaves only a small room for other Higgs bosons; (iv) the current data do not rule out pseudoscalar couplings nor pseudoscalar contributions to the Hγγand Hgg vertices; and (v) the SM Higgs boson provides the best fit to all the current Higgs data.

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arXiv2013

Implications on the Heavy CP-even Higgs Boson from Current Higgs Data

The current Large Hadron Collider data indicates that the newly observed resonance has the WW and ZZ modes consistent with the standard model Higgs boson, while the γγmode is about 1.2 - 2 times that of the standard model prediction and the tau-pair mode is suppressed. If this pattern persists in the upcoming data, it would be a sign for physics beyond the standard model. In the type II two-Higgs-doublet model, it is the region where \sinα\approx 0 and a moderately large \tanβ= 10 - 20 that the lighter CP-even Higgs boson can accommodate the current data. We note that in this region the heavier CP-even Higgs boson must have a large decay branching ratio into tau pairs. We find that this heavier Higgs boson can be observable in the associated production with a b\bar b pair and through the decay into a tau pair.

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arXiv2012

Various Models Mimicking the SM Higgs Boson

This review is based on the talk presented at the SUSY 2012 (Beijing). The new particle around 125 GeV observed at the Large Hadron Collider (LHC) is almost consistent with the standard model Higgs boson, except that the diphoton decay mode may be excessive. We summarize a number of possibilities. While at the LHC the dominant production mechanism for the Higgs boson of the standard model and some other extensions is via the gluon fusion process, the alternative vector-boson fusion is more sensitive to electroweak symmetry breaking. Using the well known dijet-tagging technique to single out the vector-boson fusion mechanism, we investigate potential of vector-boson fusion to discriminate a number of models suggested to give an enhanced inclusive diphoton production rate.

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arXiv2012

Global Study of the Simplest Scalar Phantom Dark Matter Model

We present a global study of the simplest scalar phantom dark matter model. The best fit parameters of the model are determined by simultaneously imposing (i) relic density constraint from WMAP, (ii) 225 live days data from direct experiment XENON100, (iii) upper limit of gamma-ray flux from Fermi-LAT indirect detection based on dwarf spheroidal satellite galaxies, and (iv) the Higgs boson candidate with a mass about 125 GeV and its invisible branching ratio no larger than 40% if the decay of the Higgs boson into a pair of dark matter is kinematically allowed. The allowed parameter space is then used to predict annihilation cross sections for gamma-ray lines, event rates for three processes mono-b jet, single charged lepton and two charged leptons plus missing energies at the Large Hadron Collider, as well as to evaluate the muon anomalous magnetic dipole moment for the model.

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arXiv2012

Distinguishing Various Models of the 125 GeV Boson in Vector Boson Fusion

The hint of a new particle around 125 GeV at the LHC through the decay modes of diphoton and a number of others may point to quite a number of possibilities. While at the LHC the dominant production mechanism for the Higgs boson of the standard model and some other extensions is via the gluon fusion process, the alternative vector boson fusion is more sensitive to electroweak symmetry breaking through the gauge-Higgs couplings and therefore can be used to probe for models beyond the standard model. In this work, using the well known dijet-tagging technique to single out the vector boson fusion mechanism, we investigate its capability to discriminate a number of models that have been suggested to give an enhanced inclusive diphoton production rate, including the standard model Higgs boson, fermiophobic Higgs boson, Randall-Sundrum radion, inert-Higgs-doublet model, two-Higgs-doublet model, and the MSSM. The rates in vector-boson fusion can give more information of the underlying models to help distinguishing among the models.

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