8,774 research outputs found
Origins of Hidden Sector Dark Matter I: Cosmology
We present a systematic cosmological study of a universe in which the visible
sector is coupled, albeit very weakly, to a hidden sector comprised of its own
set of particles and interactions. Assuming that dark matter (DM) resides in
the hidden sector and is charged under a stabilizing symmetry shared by both
sectors, we determine all possible origins of weak-scale DM allowed within this
broad framework. We show that DM can arise only through a handful of
mechanisms, lending particular focus to Freeze-Out and Decay and Freeze-In, as
well as their variations involving late time re-annihilations of DM and DM
particle anti-particle asymmetries. Much like standard Freeze-Out, where the
abundance of DM depends only on the annihilation cross-section of the DM
particle, these mechanisms depend only on a very small subset of physical
parameters, many of which may be measured directly at the LHC. In particular,
we show that each DM production mechanism is associated with a distinctive
window in lifetimes and cross-sections for particles which may be produced in
the near future. We evaluate prospects for employing the LHC to definitively
reconstruct the origin of DM in a companion paper.Comment: 32 pages, 19 figures; v2: references added, published versio
Measuring Slepton Masses and Mixings at the LHC
Flavor physics may help us understand theories beyond the standard model. In
the context of supersymmetry, if we can measure the masses and mixings of
sleptons and squarks, we may learn something about supersymmetry and
supersymmetry breaking. Here we consider a hybrid gauge-gravity supersymmetric
model in which the observed masses and mixings of the standard model leptons
are explained by a U(1) x U(1) flavor symmetry. In the supersymmetric sector,
the charged sleptons have reasonably large flavor mixings, and the lightest is
metastable. As a result, supersymmetric events are characterized not by missing
energy, but by heavy metastable charged particles. Many supersymmetric events
are therefore fully reconstructible, and we can reconstruct most of the charged
sleptons by working up the long supersymmetric decay chains. We obtain
promising results for both masses and mixings, and conclude that, given a
favorable model, precise measurements at the LHC may help shed light not only
on new physics, but also on the standard model flavor parameters.Comment: 24 pages; v2: fixed a typo in our computer program that led to some
miscalculated branching ratios, various clarifications and minor
improvements, conclusions unchanged, published versio
Measurement of the Superparticle Mass Spectrum in the Long-Lived Stau Scenario at the LHC
In supersymmetric scenarios with a long-lived stau, the LHC experiments
provide us with a great environment for precise mass measurements of
superparticles. We study a case in which the mass differences between the
lightest stau and other sleptons are about 10 GeV or larger, so that the decay
products of heavier sleptons are hard enough to be detected. We demonstrate
that the masses of neutralinos, sleptons, and squarks can be measured with a
good accuracy.Comment: 20 pages, 6 figure
Flavored Gauge-Mediation
The messengers of Gauge-Mediation Models can couple to standard-model matter
fields through renormalizable superpotential couplings. These matter-messenger
couplings generate generation-dependent sfermion masses and are therefore
usually forbidden by discrete symmetries. However, the non-trivial structure of
the standard-model Yukawa couplings hints at some underlying flavor theory,
which would necessarily control the sizes of the matter-messenger couplings as
well. Thus for example, if the doublet messenger and the Higgs have the same
properties under the flavor theory, the resulting messenger-lepton couplings
are parametrically of the same order as the lepton Yukawas, so that slepton
mass-splittings are similar to those of minimally-flavor-violating models and
therefore satisfy bounds on flavor-violation, with, however, slepton mixings
that are potentially large. Assuming that fermion masses are explained by a
flavor symmetry, we construct viable and natural models with messenger-lepton
couplings controlled by the flavor symmetry. The resulting slepton spectra are
unusual and interesting, with slepton mass-splittings and mixings that may be
probed at the LHC. In particular, since the new contributions are typically
negative, and since they are often larger for the first- and second-generation
sleptons, some of these examples have the selectron or the smuon as the
lightest slepton, with mass splittings of a few to tens of GeV.Comment: 16 pages v2: Explicit expressions (which are not needed in the
analysis) for the pure Yukawa contributions removed. There was an error in
some of these expressions in v1. References adde
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Land value determination in an emerging market: Empirical evidence from China
Purpose
– In this research, the purpose of this paper is to assess the relative pricing behavior for land in Beijing, China. The paper sees this as important for three core reasons. First, China has a strong growth economy but is still in many ways an undeveloped country and thus the paper do not have significant data about asset pricing behavior there. Second, China has not traditionally had a market-based land and property transfer system – thus, it is interesting to assess how prices are determined relative to typical market expectations. Third, the authors have extensive evidence on pricing behavior in the USA and Europe but little such evidence on China – are the same variables important in land pricing in China and are there other unique local variables.
Design/methodology/approach
– This paper analyzes prices of non-industrial and industrial land separately using a comprehensive data set and a semi-parametric framework. The data and flexible model specification allow the hedonic price coefficients to be estimated more accurately.
Findings
– The key results are that pricing behavior in general follows the traditional expected variables as determined by size, planning use, location and other neighborhood characteristics. However, the authors also find that land prices are associated with buyer characteristics; for example, foreign investors pay less than local investors.
Originality/value
– The study fills the gap in the literature in two ways. First, this paper analyzes prices of non-industrial and industrial land separately using a comprehensive data set and a semi-parametric framework. The data and flexible model specification allow the hedonic price coefficients to be estimated more accurately. Second, and more importantly, the authors find evidences that land prices in China are determined by both market force and “Chinese characteristics.” The land market, although established only recently, is at work. In line with the literature, determinants such as size and planning uses are found to be important in determining land prices.
This is the author's accepted manuscript. The final version has been published by Emerald Publishing Group in International Journal of Managerial Finance here: http://www.emeraldinsight.com/doi/abs/10.1108/IJMF-03-2012-0033
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Standard model and supersymmetric flavor puzzles at the CERN large hadron collider
Can the Large Hadron Collider explain the masses and mixings of the known
fermions? A promising possibility is that these masses and mixings are
determined by flavor symmetries that also govern new particles that will appear
at the LHC. We consider well-motivated examples in supersymmetry with both
gravity- and gauge-mediation. Contrary to spreading belief, new physics need
not be minimally flavor violating. We build non-minimally flavor violating
models that successfully explain all known lepton masses and mixings, but span
a wide range in their predictions for slepton flavor violation. In natural and
favorable cases, these models have metastable sleptons and are characterized by
fully reconstructible events. We outline many flavor measurements that are then
possible and describe their prospects for resolving both the standard model and
new physics flavor puzzles at the Large Hadron Collider
Stau Kinks at the LHC
The kink signature of charged tracks is predicted in some SUSY models, and it
is very characteristic signal at collider experiments. We study the kink
signature at LHC using two models, SUSY models with a gravitino LSP and a stau
NLSP, and R-parity violating SUSY models with a stau (N)LSP. We find that a
large number of kink events can be discovered in a wide range of the SUSY
parameters, when the decay length is O(10-10^5)mm. Model discrimination by
identifying the daughter particles of the kink tracks is also discussed.Comment: 19 pages, 4 figures; Version published in JHEP; abstract refined,
reference added and several minor corrections in tex
Sr, Nd Pb isotopic characteristics of granulite and pyroxenite xenoliths in Hannuoba basalts, Hebei Province, and their implications for geologic processes
Rb-Sr, Sm-Nd and Pb isotopic systematics are reported for granulite and pyroxenite xenoliths in Hannuoba basalts, Hebei Province. The isotopic characteristics of xenoliths suggest t hat they might have formed recently , although there is no strict constraint on the precise age. The decoupling of low Rb/Sr and high [87]Sr/[86]Sr ratios implies the multi-stage evolution history and strong mixing processes. There are close ties between granulite and pyroxenites with different mineral assemblages on the Sr-Nd, Pb-Sr and Pb-Nd correlation figures. The granulite is the common end-member o f the three kinds o f pyroxenite. Combined with the distribution of the xenoliths in space and their isotopic relationships, It is proposed that delamination can be well used to explain the ties.系统研究了河北汉诺坝玄武岩中二辉麻粒岩和辉石岩捕虏体的Sr、Nd、Pb 同位素特征。虽然未确定捕虏体的形成时代, 但同位素特征显示它们可能为较近期( 中生代以来) 形成。低的Rb/Sr 与高 的[87]Sr/[86]Sr 比值的解耦表明捕虏体的形成经历了较强的混合作用。在二元同位素相关图上, 三类具不同矿物组成的辉石岩与二辉麻粒岩有密切关系, 即二辉麻粒岩投点位置是三类辉石岩的共同端点。综合考虑捕虏体的空间分布及其在Sr 、Nd、Pb 同位素协变图上的关系, 可以认为层离作用可较好地解释这些现象。published_or_final_versio
下地壳及壳慢过渡带化学不均一性 -- 河北汉诺坝地区深源捕虏体元素地球化学证据
河北汉诺坝玄武岩中长英质麻粒岩、镁铁质麻粒岩和辉石岩捕虏体的主量元素和微量元素特征, 反映了下地壳及壳鳗过渡带组成具有高度化学不均一性。不相容元素原始地慢标准化曲线特征的差异表明捕虏体成因复杂。MgO 与不相容元素无或仅有很弱的相关性, 与相容元素的相关性则相对较明显。这些特征反映了下地壳及壳慢过渡带存在较强和多元的混合作用。捕虏体的加权平均值比基于麻粒岩地体资料估算的下地壳平均组成偏基性, 揭示了二者可能的成因差异。The major and trace element data of granulite and pyroxenite xenoliths, which are entrained in Hannuoba basalt Hebei Province, North China, suggest the highly chemical heterogeneity in the lower crust and crust-mantle transitional zone. There is no or only POor linear correlation between MgO and incompatible elements. Whereas a bit remarked correlations are observed between MgO and most compatible elements.The geochemical characteristics suggest that the strong and multiple mixing processes may have Occurred universally both in the lower crust and crust-mantle transitional zone. The weighed average composition of xenoliths shows a more mafic composition of the lower crust than that estimated from granulite data, which may imply the difference in the genesis.published_or_final_versio
A review of physical supply and EROI of fossil fuels in China
This paper reviews China’s future fossil fuel supply from the perspectives of physical output and net energy output. Comprehensive analyses of physical output of fossil fuels suggest that China’s total oil production will likely reach its peak, at about 230 Mt/year (or 9.6 EJ/year), in 2018; its total gas production will peak at around 350 Bcm/year (or 13.6 EJ/year) in 2040, while coal production will peak at about 4400 Mt/year (or 91.9 EJ/year) around 2020 or so. In terms of the forecast production of these fuels, there are significant differences among current studies. These differences can be mainly explained by different ultimately recoverable resources assumptions, the nature of the models used, and differences in the historical production data. Due to the future constraints on fossil fuels production, a large gap is projected to grow between domestic supply and demand, which will need to be met by increasing imports. Net energy analyses show that both coal and oil and gas production show a steady declining trend of EROI (energy return on investment) due to the depletion of shallow-buried coal resources and conventional oil and gas resources, which is generally consistent with the approaching peaks of physical production of fossil fuels. The peaks of fossil fuels production, coupled with the decline in EROI ratios, are likely to challenge the sustainable development of Chinese society unless new abundant energy resources with high EROI values can be found
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