分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： It was suggested that the $\gamma$-ray halo around Geminga might not be interpreted by slow-diffusion. If the ballistic regime of electron/positron propagation is considered, the Geminga halo may be explained even with a large diffusion coefficient. In this work, we examine this effect by taking the generalized J\"uttner propagator as the approximate relativistic Green's function for diffusion and find that the morphology of the Geminga halo can be marginally fitted in the fast-diffusion scenario. However, the recently discovered $\gamma$-ray halo around PSR J0622$+$3749 at LHAASO cannot be explained by the same effect and slow diffusion is the only solution. Furthermore, both the two pulsar halos require a conversion efficiency from the pulsar spin-down energy to the high energy electrons/positrons much larger than 100\%, if they are interpreted by this ballistic transport effect. Therefore, we conclude that slow diffusion is necessary to account for the $\gamma$-ray halos around pulsars.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-11-10
摘要： We study natural supersymmetry in the Generalized Minimal Supergravity (GmSUGRA).For the parameter space with low energy electroweak fine-tuning measures less than 50, we are left with only the Z-pole, Higgs-pole and Higgsino LSP scenarios for dark matter (DM). We perform the focused scans for such parameter space and find that it satisfies various phenomenological constraints and is compatible with the current direct detection bound on neutralino DM reported by the LUX experiment. Such parameter space also has solutions with correct DM relic density besides the solutions with DM relic density smaller or larger than 5 WMAP9 bounds. We present five benchmark points as examples. In these benchmark points, gluino and the first two generations of squarks are heavier than 2 TeV, stop ˜t1,2 are in the mass range [1, 2] TeV, while sleptons are lighter than 1 TeV. Some part of the parameter space can explain the muon anomalous magnetic moment within 3 as well. We also perform the collider study of such solutions by implementing and comparing with relevant studies done by the ATLAS and CMS Collaborations. We find that the points with Higgsino dominant ˜ 02/ ˜ ±1 mass upto 300 GeV are excluded in Z-pole scenario while for Higgs-pole scenario, the points with ˜ 02 mass up to 460 GeV are excluded. We also notice that the Higgsino LSP points in our present scans are beyond the reach of present LHC searches. Next, we show that for both the Z-pole and Higgs-pole scenarios, the points with electroweak fine-tuning measure around 20 do still survive.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-11-10
摘要： Recently the AMS-02 collaboration has published the measurement of the cosmic antiproton to proton ratio p¯/p and the p¯ flux with a high precision up to ∼ 450 GeV. In this work, we perform a systematic analysis of the secondary antiproton flux generated by the cosmic ray interaction with the interstellar gas. The uncertainty of the prediction originates from the cosmic ray propagation process and the hadronic interaction models. Although the cosmic ray propagation parameters have been well controlled by the AMS-02 B/C ratio data for a specified model, different propagation models can not be discriminated by the B/C data. The p¯ flux is also calculated for several hadronic interaction models, which are generally adopted by the cosmic ray community. However, the results for different hadronic models do not converge. We find the EPOS LHC model, which seems to fit the collider data very well, predicts a slightly lower p¯/p ratio than the AMS-02 data at the high energy end. Finally we derive the constraints on the dark matter annihilation cross section from the AMS-02 p¯/p ratio for different propagation and hadronic interaction models.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-11-10
摘要： The AMS-02 has measured the cosmic ray electron (plus positron) spectrum up to ∼TeV with an unprecedent precision. The spectrum can be well described by a power law without any obvious features above 10 GeV. The satellite instrument Dark Matter Particle Explorer (DAMPE), which was launched a year ago, will measure the electron spectrum up to 10 TeV with a high energy resolution. The cosmic electrons beyond TeV may be attributed to few local cosmic ray sources, such as supernova remnants. Therefore, spectral features, such as cutoff and bumps, can be expected at high energies. In this work we give a careful study on the perspective of the electron spectrum beyond TeV. We first examine our astrophysical source models on the latest leptonic data of AMS-02 to give a self-consistent picture. Then we focus on the discussion about the candidate sources which could be electron contributors above TeV. Depending on the properties of the local sources (especially on the nature of Vela), DAMPE may detect interesting features in the electron spectrum above TeV in the future.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-11-10
摘要： Growing evidence reveals universal hardening on various cosmic ray spectra, e.g. proton, positron, as well as antiproton fraction. Such universality may indicate they have a common origin. In this paper, we argue that these widespread excesses can be accounted for by a nearby supernova remnant surrounded by a giant molecular cloud. Secondary cosmic rays (p, e+) are produced through the collisions between the primary cosmic ray nuclei from this supernova remnant and the molecular gas. Different from the background, which is produced by the ensemble of large amount of sources in the Milky Way, the local injected spectrum can be harder. The time-dependent transport of particles would make the propagated spectrum even harder. Under this scenario, the anomalies of both primary (p, e−) and secondary (e+, ¯p/p) cosmic rays can be properly interpreted. We further show that the TeV to sub-PeV anisotropy of proton is consistent with the observations if the local source is relatively young and lying at the anti-Galactic center direction.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2017-08-03
摘要： The gamma-ray excess observed by the Fermi-LAT in the Galactic Center can be interpreted by the dark matter annihilation to b ¯b via a light pseudoscalar in the NMSSM. It is interesting to note that the corresponding singlet scalar is useful to achieve a strongly first order phase transition required by the electroweak baryogenesis. In this paper, we investigate the possibility that the NMSSM model can simultaneously accommodate these two issues. The phase transition strength can be characterized by the vacua energy gap at zero temperature and be sufficiently enhanced by the tree-level effect in the NMSSM. We find that the annihilation of Singlino/Higgsino DM particles occurring close to the light pseudoscalar resonance is favored by the galactic center excess and the observed DM relic density, and a resulting small κ/λ and a negative Aκ can also lead to a successful strongly first order electroweak phase transition
分类： 物理学 >> 核物理学 提交时间： 2016-09-22
摘要： Recently, an excess of events in diphoton channel with invariant mass of about 750 GeV has been reported by the ATLAS and CMS Collaborations. Considering it as a tantalizing hint for new physics beyond the Standard Model (SM), we propose a simple extension of the SM with an additional doublet Higgs H′ and a singlet s. We consider the neutral component H′0 of H′ as the 750 GeV resonance, and assume that s is lighter than 2.6 GeV. In particular, H′0 can be produced at tree level via qq¯ production, and decay into a pair of s at tree level. And then s can decay into a pair of collimated photons, which cannot be distinguished at the LHC. We show that the diphoton production cross section can be from 3 to 13 fb, the decay width of H′0 can be from 30 to 60 GeV, and all the current experimental constraints including dijet constraint can be satisfied.
分类： 物理学 >> 核物理学 提交时间： 2016-09-19
摘要： The recent reported 750 GeV diphoton excess at the 13 TeV LHC is explained in the framework of effective field theory assuming the diphoton resonance is a scalar (pseudoscalar) particle. It is found that the large production rate and the broad width of this resonance are hard to simultaneously explain if only visible final states are considered. Therefore an invisible decay channel to dark matter (DM) is strongly favored by the diphoton excess with a broad width, given a large coupling of the new scalar to DM. We set constraints on the parameter space in this scenario using the results from LHC Run 1, DM relic density, and DM direct and indirect detection experiments. We find that the DM searches can exclude a large portion of the parameter regions accounting for the diphoton excess with a broad width.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： The AMS-02 collaboration has just released the cosmic antiproton to proton ratio p¯/p with a high precision up to ∼450 GeV. In this work, we calculate the secondary antiprotons generated by cosmic ray interactions with the interstellar medium taking into account the uncertainties from the cosmic ray propagation. The p¯/p ratio predicted by these processes shows some tension with the AMS-02 data in some regions of propagation parameters, but the excess is not significant. We then try to derive upper bounds on the dark matter annihilation cross section from the p¯/p data or signal regions favored by the data. It is shown that the constraint derived by the AMS-02 data is similar to that from Fermi-LAT observations of dwarf galaxies. The signal region for dark matter is usually required mχ∼O(10) TeV and $\left\sim\mathcal{O}(10^{-23})~\cm^3~\sec^{-1}$.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： The gamma-ray excess observed by the Fermi-LAT in the Galactic Center can be interpreted by the dark matter annihilation to bb¯ via a light pseudoscalar in the NMSSM. It is interesting to note that the corresponding singlet scalar is useful to achieve a strongly first order phase transition required by the electroweak baryogenesis. In this paper, we investigate the possibility that the NMSSM model can simultaneously accommodate these two issues. The phase transition strength can be characterized by the vacua energy gap at zero temperature and be sufficiently enhanced by the tree-level effect in the NMSSM. We find that the annihilation of Singlino/Higgsino DM particles occurring close to the light pseudoscalar resonance is favored by the galactic center excess and the observed DM relic density, and a resulting small κ/λ and a negative Aκ can also lead to a successful strongly first order electroweak phase transition.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： We study the prospect of dark matter (DM) searches in the monojet channel at future pp colliders with center-of-mass energies of 33, 50, and 100~TeV. We consider a class of simplified models in which a vector boson connecting DM particles to quarks is introduced. Comparing with studies in the effective field theory, the present framework gives more reasonable production rates and kinematics of the DM signatures. We estimate the sensitivities of future colliders with an integrated luminosity of 3 ab−1 to the DM-induced monojet signature and show the parameter space that can be explored. The constraints from direct and indirect DM detection experiments are compared with the future collider sensitivities. We find that the future collider detection will be much more sensitive than the indirect detection for the vector interaction, and have better sensitivities than those of the direct detection by several orders of magnitude for the axial vector interaction.
分类： 物理学 >> 核物理学 提交时间： 2016-09-06
摘要： We study a simplified scenario in the next-to-minimal supersymmetric standard model with a split electroweak spectrum, in which only the singlino and higgsinos are light and other superpartners are decoupled. Serving as a dark matter candidate, a singlino-dominated neutralino χ~01 should have either resonant annihilation effects or sizable higgsino components to satisfy the observed relic abundance. The sensitivities of LHC searches and dark matter detection experiments are investigated. With an integrated luminosity of 30(300)fb−1, $3l + \missET$ and $2l + \missET$ searches at the 13 (14) TeV LHC are expected to reach up to $m_{\chia}\sim 150 (270) \mathrm{GeV}$ and mχ~02,χ~±1∼320(500)GeV. Near future dark matter direct and indirect detection experiments can cover some parameter regions where collider searches lose their sensitivities.
分类： 物理学 >> 核物理学 提交时间： 2016-08-31
摘要： We propose a novel framework for asymmetric scalar dark matter (ADM), which has interesting collider phenomenology in terms of an unstable ADM bound state (ADMonium) produced via Higgs portals. ADMonium is a natural consequence of the basic features of ADM: the (complex scalar) ADM is charged under a dark local U(1)d symmetry which is broken at a low scale and provides a light gauge boson X. The dark gauge coupling is strong and then ADM can annihilate away into X-pair effectively. Therefore, the ADM can form bound state due to its large self-interaction via X mediation. To explore the collider signature of ADMonium, we propose that ADM has a two-Higgs doublet portal. The ADMonium can have a sizable mixing with the heavier Higgs boson, which admits a large cross section of ADMonium production associated with bb¯. Of particular interest, our setup nicely explains the recent di-photon anomaly at 750 GeV via the events from ${\rm ADMonium}\ra 2X(\ra e^+e^-)$, where the electrons are identified as (un)converted photons. The remarkable prediction of an ADM near 375 GeV can be tested at the direct detection experiments in the near future.
分类： 物理学 >> 核物理学 提交时间： 2016-08-30
摘要： The gamma-ray observation of dwarf spheroidal satellites (dSphs) is an ideal approach for probing the dark matter (DM) annihilation signature. The latest Fermi-LAT dSph searches have set stringent constraints on the velocity independent annihilation cross section in the small DM mass range, which gives very strong constraints on the scenario to explain the the AMS-02 positron excess by DM annihilation. However, the dSph constraints would change in the velocity dependent annihilation scenarios, because the velocity dispersion in the dSphs varies from that in the Milky Way. In this work, we use a likelihood map method to set constraints on the velocity dependent annihilation cross section from the Fermi-LAT observation of six dSphs. We consider three typical forms of the annihilation cross section, i.e. p-wave annihilation, Sommerfeld enhancement, and Breit-Wigner resonance. For the p-wave annihilation and Sommerfeld-enhancement, the dSph limits would become much weaker and stronger compared with those for the velocity independent annihilation, respectively. For the Breit-Wigner annihilation, the dSph limits would vary depending on the model parameters. We show that the scenario to explain the AMS-02 positron excess by DM annihilation is still viable in the velocity dependent cases
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