arXiv subjects

Haipeng An

Publications and source records attributed to Haipeng An.

At least 55 records · Page 3Linked to original sources

arXiv2020

New limits on dark photons from solar emission and keV scale dark matter

We provide updates to the limits on solar emission of dark photons, or more generally any light vector particle coupled to the electron vector current. The recent 2019 and 2020 electronic recoil data from XENON1T now provides more stringent constraints on these models than stellar energy loss in the sub-keV mass region. We also show that solar emission of dark photons does not provide a good fit to the recent XENON1T excess in the 2-5 keV energy bins. In contrast, the absorption of 2-4 keV mass dark photons that saturate the local dark matter mass density does provide a good fit to the excess, for mixing angles in the range $ε\in (4-12)\times 10^{-16}$, while satisfying astrophysical constraints. Similarly, other models utilizing the vector portal can fit the excess, including those with operators that directly couple the dark photon field strength to electron spin.

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arXiv2020

Self-Interacting Dark Matter and the Origin of Ultra-Diffuse Galaxies NGC1052-DF2 and -DF4

Observations of ultra-diffuse galaxies NGC 1052-DF2 and -DF4 show they may contain little dark matter, challenging our understanding of galaxy formation. Using controlled N-body simulations, we explore the possibility that their properties can be reproduced through tidal stripping from the elliptical galaxy NGC 1052, in both cold dark matter (CDM) and self-interacting dark matter (SIDM) scenarios. To explain the dark matter deficiency, we find that a CDM halo must have a very low concentration so that it can lose sufficient inner mass in the tidal field. In contrast, SIDM favors a higher and more reasonable concentration as core formation enhances tidal mass loss. Final stellar distributions in our SIDM benchmarks are more diffuse than the CDM one, and hence the former are in better agreement with the data. We further show that a cored CDM halo model modified by strong baryonic feedback is unlikely to reproduce the observations. Our results indicate that SIDM is more favorable for the formation of dark-matter-deficient galaxies.

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arXiv2018

KeV Scale Frozen-in Self-Interacting Fermionic Dark Matter

We present a model in which the dark matter particle is frozen-in at MeV scale. In this model, the mediator between the standard model sector and the dark sector can automatically provide a self-interaction for dark matter. The interaction strength is naturally to be the in the region in favor of the cluster mass deficit anomaly. Due to the self-scattering, the Lyman-$α$ constraint can be relaxed to $m_D \gtrsim 2 $ keV. In this region the self-interaction and the Fermi pressure both play roles on forming a dark matter core at the center of the dwarf galaxies.

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arXiv2018

Directly Detecting MeV-scale Dark Matter via Solar Reflection

If dark matter (DM) particles are lighter than a few MeV/$c^2$ and can scatter off electrons, their interaction within the solar interior results in a considerable hardening of the spectrum of galactic dark matter received on Earth. For a large range of the mass vs. cross section parameter space, $\{m_e, σ_e\}$, the "reflected" component of the DM flux is far more energetic than the endpoint of the ambient galactic DM energy distribution, making it detectable with existing DM detectors sensitive to an energy deposition of $10-10^3$ eV. After numerically simulating the small reflected component of the DM flux, we calculate its subsequent signal due to scattering on detector electrons, deriving new constraints on $σ_e$ in the MeV and sub-MeV range using existing data from the XENON10/100, LUX, PandaX-II, and XENON1T experiments, as well as making projections for future low threshold direct detection experiments.

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arXiv2018

De Sitter Quantum Loops as the origin of Primordial Non-Gaussianities

It was pointed out recently that in some inflationary models quantum loops containing a scalar of mass $m$ that couples to the inflaton can be the dominant source of primordial non-Gaussianities. We explore this phenomenon in the simplest such model focusing on the behavior of the primordial curvature fluctuations for small $m/H$. Explicit calculations are done for the three and four point curvature fluctuation correlations. Constraints on the parameters of the model from the CMB limits on primordial non-Gaussianity are discussed. The bi-spectrum in the squeezed limit and the tri-spectrum in the compressed limit are examined. The form of the $n$-point correlations as any partial sum of wave vectors get small is determined.

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arXiv2018

The Direct Coupling of Light Quarks to Heavy Di-quarks

In the limit $m_Q >m_Q v_{\rm rel} > m_Q v_{\rm rel}^2 \gg Λ_{QCD}$ hadronic states with two heavy quarks $Q$ should be describable by a version of HQET where the heavy quark is replaced by a di-quark degree of freedom. In this limit the di-quark is a small (compared with $1/Λ_{QCD}$) color anti-triplet, bound primarily by a color Coulomb potential. The excited Coulombic states and color six states are much heavier than the color anti-triplet ground state. The low lying spectrum of hadrons containing two heavy quarks is then determined by the coupling of the light quarks and gluons with a momentum of order $Λ_{QCD}$ to this ground state di-quark. In this short paper we calculate the coefficient of leading local operator $\left( S_v^{\dagger} S_v\right) \left({\bar q} {γ^μ v_μ } q\right) $ that couples this color-triplet di-quark field $S_v$ (with four-velocity $v$) directly to the light quarks $q$ in the low energy effective theory. It is ${\cal O}(1/( α_s(m_Q v_{\rm rel}) m_Q^2))$. While our work is mostly of pedagogical value we make an estimate of the contribution of this operator to the masses of $Ξ_{bbq}$ baryon and $T_{QQ{\bar q} {\bar q}}$ tetraquark using the non-relativistic constituent quark model.

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arXiv2017

Quasi Single Field Inflation in the non-perturbative regime

In quasi single field inflation there are massive fields that interact with the inflaton field. If these other fields are not much heavier than the Hubble constant during inflation ($H$) these interactions can lead to important consequences for the cosmological energy density perturbations. The simplest model of this type has a real scalar inflaton field that interacts with another real scalar $S$ (with mass $m$). In this model there is a mixing term of the form $μ{\dot π} S$, where $π$ is the Goldstone fluctuation that is associated with the breaking of time translation invariance by the time evolution of the inflaton field during the inflationary era. In this paper we study this model in the region $(μ/H )^2 +(m/H)^2 >9/4$ and $m/H \sim {\cal O}(1)$ or less. For a large part of the parameter space in this region standard perturbative methods are not applicable. Using numerical and analytic methods we derive a number of new results. In addition we study how large $μ/H$ has to be for the large $μ/H$ effective field theory approach to be applicable.

hep-ph↗

arXiv2017

Non-Gaussian Enhancements of Galactic Halo Correlations in Quasi-Single Field Inflation

We consider a quasi-single field inflation model in which the inflaton interacts with a massive scalar field called the isocurvaton. Due to the breaking of time translational invariance by the inflaton background, these interactions induce kinetic mixing between the inflaton and isocurvaton, which is parameterized by a constant $μ$. We derive analytic formulae for the curvature perturbation two-, three-, four-, five-, and six-point functions explicitly in terms of the external wave-vectors in the limit where $μ$ and the mass of the isocurvaton $m$ are both much smaller than $H$. In previous work, it has been noted that when $m/H$ and $μ/H$ are small, the non-Gaussianities predicted by quasi-single field inflation give rise to long wavelength enhancements of the power spectrum for biased objects (e.g., galactic halos). We review this calculation, and calculate the analogous enhanced contribution to the bispectrum of biased objects. We determine the scale at which these enhanced terms are larger than the Gaussian piece. We also identify the scaling of these enhanced parts to the $n$-point function of biased objects.

hep-ph↗

arXiv2017

Exploring the nearly degenerate stop region with sbottom decays

A light stop with mass almost degenerate with the lightest neutralino has important connections with both naturalness and dark matter relic abundance. This region is also very hard to probe at colliders. In this paper, we demonstrate the potential of searching for such stop particles at the LHC from sbottom decays, focusing on two channels with final states $2\ell+E^{\rm miss}_{\rm T}$ and $1b1\ell+E^{\rm miss}_{\rm T}$. We found that, if the lightest sbottom has mass around or below 1 TeV and has a significant branching ratio to decay to stop and $W$ ($\tilde{b} \to \tilde{t}\,W$), a stop almost degenerate with neutralino can be excluded up to about 500-600 GeV at the 13 TeV LHC with $300\,{\rm fb}^{-1}$ data. The searches we propose are complementary to other SUSY searches at the LHC and could have the best sensitivity to the stop-bino coannihilation region. Since they involve final states which have already been used in LHC searches, a reinterpretation of the search results already has sensitivity. Further optimization could deliver the full potential of these channels.

hep-ph↗

arXiv2016

Dark Sectors 2016 Workshop: Community Report

This report, based on the Dark Sectors workshop at SLAC in April 2016, summarizes the scientific importance of searches for dark sector dark matter and forces at masses beneath the weak-scale, the status of this broad international field, the important milestones motivating future exploration, and promising experimental opportunities to reach these milestones over the next 5-10 years.

hep-ph↗

arXiv2016

Strong CMB Constraint On P-Wave Annihilating Dark Matter

We consider a dark sector consisting of dark matter that is a Dirac fermion and a scalar mediator. This model has been extensively studied in the past. If the scalar couples to the dark matter in a parity conserving manner then dark matter annihilation to two mediators is dominated by the P-wave channel and hence is suppressed at very low momentum. The indirect detection constraint from the anisotropy of the Cosmic Microwave Background is usually thought to be absent in the model because of this suppression. In this letter we show that dark matter annihilation to bound states occurs through the S-wave and hence there is a constraint on the parameter space of the model from the Cosmic Microwave Background.

hep-ph↗

arXiv2016

Effects of Bound States on Dark Matter Annihilation

We study the impact of bound state formation on dark matter annihilation rates in models where dark matter interacts via a light mediator, the dark photon. We derive the general cross section for radiative capture into all possible bound states, and point out its non-trivial dependence on the dark matter velocity and the dark photon mass. For indirect detection, our result shows that dark matter annihilation inside bound states can play an important role in enhancing signal rates over the rate for direct dark matter annihilation with Sommerfeld enhancement. The effects are strongest for large dark gauge coupling and when the dark photon mass is smaller than the typical momentum of dark matter in the galaxy. As an example, we show that for thermal dark matter the Fermi gamma ray constraint is substantially increased once bound state effects are taken into account. We also find that bound state effects are not important for dark matter annihilation during the freeze out and recombination epochs.

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arXiv2015

Broad Diphotons from Narrow States

ATLAS and CMS have each reported a modest diphoton excess consistent with the decay of a broad resonance at ~ 750 GeV. We show how this signal can arise in a weakly coupled theory comprised solely of narrow width particles. In particular, if the decaying particle is produced off-shell, then the associated diphoton resonance will have a broad, adjustable width. We present simplified models which explain the diphoton excess through the three-body decay of a scalar or fermion. Our minimal ultraviolet completion is a weakly coupled and renormalizable theory of a singlet scalar plus a heavy vector-like quark and lepton. The smoking gun of this mechanism is an asymmetric diphoton peak recoiling against missing transverse energy, jets, or leptons.

hep-ph↗

arXiv2015

Opening up the compressed region of stop searches at 13 TeV LHC

Light top superpartners play a key role in stabilizing the electroweak scale in supersymmetric theories. For $R$-parity conserved supersymmetric models, traditional searches are not sensitive to the compressed regions. In this paper, we propose a new method targeting this region, with stop and neutralino mass splitting ranging from $m_{\tilde t} - m_χ\gtrsim m_t$ to about 20 GeV. In particular, we focus on the signal process in which a pair of stops are produced in association with a hard jet, and define a new observable $R_M$ whose distribution has a peak in this compressed region. The position of the peak is closely correlated with $m_{\tilde t}$. We show that for 13 TeV LHC with a luminosity of 3000 fb$^{-1}$, this analysis can extend the reach of stop in the compressed region to $m_{\tilde t}$ around 800 GeV.

hep-ph↗

arXiv2015

Direct detection prospects of dark vectors with xenon-based dark matter experiments

Dark matter experiments primarily search for the scattering of WIMPs on target nuclei of well shielded underground detectors. The results from liquid scintillator experiments furthermore provide precise probes of very light and very weakly coupled particles that may be absorbed by electrons. In these proceedings we summarize previously obtained constraints on long-lived dark matter vector particles $V$ (dark photons) in the $0.01-100$ keV mass range. In addition, we provide a first projected sensitivity reach for the upcoming XENON1T dark matter search to detect dark photons.

hep-ph↗

arXiv2015

Direct Detection Constraints on Dark Photon Dark Matter

Dark matter detectors built primarily to probe elastic scattering of WIMPs on nuclei are also precise probes of light, weakly coupled particles that may be absorbed by the detector material. In this paper, we derive constraints on the minimal model of dark matter comprised of long-lived vector states V (dark photons) in the 0.01-100 keV mass range. The absence of an ionization signal in direct detection experiments such as XENON10 and XENON100 places a very strong constraint on the dark photon mixing angle, down to $O(10^{-15})$, assuming that dark photons comprise the dominant fraction of dark matter. This sensitivity to dark photon dark matter exceeds the indirect bounds derived from stellar energy loss considerations over a significant fraction of the available mass range. We also revisit indirect constraints from $V\to 3γ$ decay and show that limits from modifications to the cosmological ionization history are comparable to the updated limits from the diffuse gamma-ray flux.

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arXiv2014

Dark matter with $t$-channel mediator: a simple step beyond contact interaction

Effective contact operators provide the simplest parameterization of dark matter searches at colliders. However, light mediator can significantly change the sensitivity and search strategies. Considering simple models of mediators is an important next-step for collider searches. In this paper, we consider the case of a $t$-channel mediator. Its presence opens up new contributions to the monojet$+\displaystyle{\not{E}}_T$ searches and can change the reach significantly. We also study the complementarity between searches for processes of monojet$+\displaystyle{\not{E}}_T$ and direct pair production of the mediators. Mediator pair production also gives important contribution to a CMS-like monojet$+\displaystyle{\not{E}}_T$ search where a second hard jet is allowed.There is a large region of parameter space in which the monojet$+\displaystyle{\not{E}}_T$ search provides the stronger limit. Assuming the relic abundance of the dark matter is thermally produced within the framework of this model, we find that in the Dirac fermion dark matter case, there is no region in the parameter space that satisfies the combined constraint of monojet$+\displaystyle{\not{E}}_T$ search and direct detection; whereas in the Majorana fermion dark matter case, the mass of dark matter must be larger than about 100 GeV. If the relic abundance requirement is not assumed, the discovery of the $t$-channel mediator predicts additional new physics.

hep-ph↗

arXiv2014

Observing dark photon with dark matter detectors

Motivated by various kinds of new physics models, a new light neutral vector boson (the dark photon) connected to the Standard Model of particle physics only through the kinetic mixing with the U(1)_Y factor has been studied extensively. Various kinds of experiments are proposed to detect it. For the dark photon with a mass smaller than 10 keV, it can be copiously produced inside the Sun, and then be detected by the detectors on the earth. We show that with the S2 only analysis, the result from XENON10 experiment provides the up-to-date most stringent limit on the region 10^{-5} eV < m_V < 10^3 eV: kappa m_V < 3 times 10^{-12} eV for the Stueckelberg dark photon model, where kappa is the kinetic mixing and m_V is the mass of the dark photon. If there is a light Higgs boson accompanied with the dark photon, the sensitivity of XENON10 experiment is kappa times e' < 10^{-13}, which is still second to the constraints from the lifetime of horizontal branch starts which dictates kappa times e' < 3 times10^{-14}.

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