基于混合Copula的CDO定价模型

将广受欢迎的,用于CDO定价的大样本同质投资组合近似方法做了推广,其中涉及到的分布是高斯分布和Variance Gamma分布的混合,即G-VG混合分布.提出了厚尾的G-VG混合Copula模型和带有随机相关性的混合模型.这些模型可以有效的模拟CDO定价中的"相关性微笑"问题.在这些G-VG混合Copula模型中,得到了损失分布函数和期望分券层损失的解析表达式.并且用实际数据做了实证分析,把新模型和高斯模型的结果做了比较.实证表明,新模型的结果不仅与市场报价更贴近,而且为相关性结构带来了更多的灵活性.     

基于混合分布单因子模型的CDO定价问题

本文讨论了基于混合分布单因子模型的CDO定价问题,在所研究的CDO抵押资产组合中,描述资产价值的市场共同因子和异质因子均服从标准高斯和NIG的混合分布,且相关系数为随机相关系数.通过半解析法给出了CDO分券层的公允价格公式,并利用傅里叶变换及其逆变换,得出了贝努利相关和三状态相关两种随机相关系数的情形下累积损失概率分布的求解方法.     

担保债权凭证定价——Copula函数的非参数估计与应用

CDO是最近十年来规模增长最快的信用衍生产品之一.2005年国家开发银行和建设银行两只资产支持证券的发行开启了我国CDO市场的先河,因此,深入分析CDO的合理定价不仅是当前金融研究中一个备受关注的问题也是促进CDO市场在我国健康发展的要求.对CDO定价要求模型化违约相关关系,普遍使用的方法是指定一个Copula函数来描述这种相关关系,然后使用市场数据来估计其中的参数.这种参数分析法方法不可避免的会导致巨大的模型风险.使用非参数方法可以从市场数据中推导出一个合理的Copula函数,然后利用Monte Carlo方法计算CDO分券的合理价差.这不仅可以避免因市场数据存在“厚尾”现象而错误估计Pearson相关系数带来的定价误差,还可以利用估计出来的Copula函数很方便地计算Kendall＇sτ、Spearman＇sρ等依赖性测度的值.     

金融危机与一般均衡下的CDO定价

传统的CDO根据无套利原理,将信用风险的保险费和违约后的回收金额两个现金流进行复制得出定价,注重金融市场局部均衡.然而无套利均衡定价的思路只针对存在套利机会的资产市场的局部均衡,使得该均衡与基础资产的联系不强.而一般均衡分析,可以引入实体经济的因素,有利于防止CDO定价的泡沫风险.因此文章在CDO定价中引入实体经济要素,证明一般均衡下CDO定价相比无套利定价有更丰富更敏感的风险刻画能力.实证结果发现,一般均衡定价相当于无套利定价加上修正项,且在高风险时期两者价差高于低风险时期,这是由于无套利定价忽略了实体经济的风险.因此CDO产品的无套利定价很可能存在着泡沫而导致资源配置扭曲.最后,文章认为CDO可以预防定价风险,用于解决地方政府债务问题,并提出相关的风险控制建议.     

多参数Archimedean Copula模型下的CDO定价

利用高维Archimedean Copula模型对合成CDO进行定价,在传统简单Archimedean Copula的基础上,基于三种不同的方式,引入多个参数,从而解决作为市场基准的Gaussian Copula模型下存在相关性微笑的问题.对于特殊的大样本同质资产组合,违约损失分布可以直接从违约概率得到.而对于一般性的资产组合,可以得到损失的特征函数,从而通过快速Fourier变换,计算出违约的分布.最后,给出了数值计算结果.     

多损失条件风险值的多层规划模型

对于多个损失函数,在给定的置信水平下,首先定义了不超过给定损失值的最小风险值(即Va R值)和基于权值的累积期望损失值(即CVa R损失值)概念,然后建立了一个多损失条件风险值的多层规划模型.该模型的目标是求各层多损失CVa R值达最小的最优策略,并证明了它等价于另一个较容易求解的多层规划模型.最后,给出了三级供应链中多产品的定价与订购的条件风险值模型(三层线性规划模型).     

资本资产定价研究:基于损失厌恶、追赶时髦和习惯形成的新进展

为了推进资产定价理论的研究以及更好的解释重要的市场异象,本文通过在效用函数中引入投资者的异质假定,构造了一个投资者偏好由习惯形成,追赶时髦以及损失厌恶共同决定的效用函数,并在这个更加真实的效用函数的基础上建立了一个能够更好的解释市场异象的新的消费基础资本资产定价模型.另外,文章运用欧拉方程推出了模型的资产收益定价方程.通过定价方程,我们可以期望更好的同时解释溢价之谜,无风险利率之谜等重要的市场异象.这证明了引入合理的行为偏好才是解决股票溢价等问题的关键.     

跳跃-扩散模型中期权定价的倒向随机微分方程方法及等价概率鞅测度

本文研究的是跳跃一扩散模型中的期权定价问题.通过研究该模型中未定权益所对应的倒向随机微分方程,找到市场中的-个等价概率鞅测度,借助测度变换,未定权益的定价问题就可转化为在等价概率鞅测度下的求期望问题.利用该方法,本文解得了标的股票价格过程为带非时齐:Poisson跳跃的扩散过程且股价期望增长率,波动率,无风险利率均为时间函数时欧式期权价格公式.并且,借助倒向随机微分方程找到在以上参数均为常数时,期权价格所满足的偏微分方程.     

跨期多事件触发巨灾债券定价模拟分析

巨灾导致的不同类损失分布具有异质性,而单一事件触发的巨灾债券不能统筹考虑多个损失维度.本文在考虑两个不同损失维度的基础上,构建了由两个损失指标共同触发的巨灾债券定价模型,进行了产品初步设计和价格估算,并通过蒙特卡罗模拟实现了多期限定价.本文以台风损失为例,对直接经济损失、受灾面积两个损失维度进行分布拟合,借助ClaytonCopula得到联合概率分布函数对巨灾债券定价,并进行了价格动态分析.     

认股权证的修正精算定价研究

基于修正Bladt和Rydberg在无市场假设下关于期权定价的保险精算方法的基础上,从评估实际损失和相应概率分布角度,利用公平保费原则建立认股权证的定价模型,并给出定价公式.且当投资者对原生资产期望回报率为无风险利率时,该定价为风险中性价格.     

Calibrating probability distributions with convex-concave-convex functions: application to CDO pricing

This paper considers a class of functions referred to as convex-concave-convex (CCC) functions to calibrate unimodal or multimodal probability distributions. In discrete case, this class of functions can be expressed by a system of linear constraints and incorporated into an optimization problem. We use CCC functions for calibrating a risk-neutral probability distribution of obligors default intensities (hazard rates) in collateral debt obligations (CDO). The optimal distribution is calculated by maximizing the entropy function with no-arbitrage constraints given by bid and ask prices of CDO tranches. Such distribution reflects the views of market participants on the future market environments. We provide an explanation of why CCC functions may be applicable for capturing a non-data information about the considered distribution. The numerical experiments conducted on market quotes for the iTraxx index with different maturities and starting dates support our ideas and demonstrate that the proposed approach has stable performance. Distribution generalizations with multiple humps and their applications in credit risk are also discussed.     

Comparison results for exchangeable credit risk portfolios

This paper is dedicated to risk analysis of credit portfolios. Assuming that default indicators form an exchangeable sequence of Bernoulli random variables and as a consequence of de Finetti’s theorem, default indicators are Binomial mixtures. We can characterize the supermodular order between two exchangeable Bernoulli random vectors in terms of the convex ordering of their corresponding mixture distributions. Thus we can proceed to some comparisons between stop-loss premiums, CDO tranche premiums and convex risk measures on aggregate losses. This methodology provides a unified analysis of dependence for a number of CDO pricing models based on factor copulas, multivariate Poisson and structural approaches.     

卖空约束下的公司债券定价

信用溢价之谜是近年来在资产定价领域中热点研究问题之一,本文试图从结构化模型角度对这一问题做出解释。通过引入市场卖空约束条件,我们建立了新的公司债券定价模型。由于卖空约束在现实市场中普遍存在,因此建立这种结构化模型是具有实际意义的。实证研究表明该模型可以得出比现有模型更高的信用溢价,能很好地解释信用溢价之谜。     

Asset portfolio securitizations and cyclicality of regulatory capital

This paper analyzes the level and cyclicality of regulatory bank capital for asset portfolio securitizations in relation to the cyclicality of capital requirements for the underlying loan portfolio as under Basel II/III. We find that the cyclicality of capital requirements is higher for (i) asset portfolio securitizations relative to primary loan portfolios, (ii) Ratings Based Approach (RBA) relative to the Supervisory Formula Approach, (iii) given the RBA for a point-in-time rating methodology relative to a rate-and-forget rating methodology, and (iv) under the passive reinvestment rule relative to alternative rules. Capital requirements of the individual tranches reveal that the volatility of aggregated capital charges for the securitized portfolio is triggered by the most senior tranches. This is due to the fact that senior tranches are more sensitive to the macroeconomy. An empirical analysis provides evidence that current credit ratings are time-constant and that economic losses for securitizations have exceeded the required capital in the recent financial crisis.     

A stochastic partial differential equation model for the pricing of mortgage-backed securities

We develop a dynamic structural model for the wealth of individual mortgagors in a mortgage pool. We model the process of default and prepayment and, by taking a limit as the pool size goes to infinity, derive a stochastic partial differential equation (SPDE) which can be used to describe the evolution of the loss process from the pool. We prove existence and uniqueness of solutions to this SPDE and show how our model is able to capture, in a flexible way, the prices of credit risky tranches of mortgage-backed securities under different market conditions.     

Importance sampling for integrated market and credit portfolio models

A sophisticated approach for computing the total economic capital needed for various stochastically dependent risk types is the bottom-up approach. In this approach, usually, market and credit risks of financial instruments are modeled simultaneously. As integrating market risk factors into standard credit portfolio models increases the computational burden of calculating risk measures, it is analyzed to which extent importance sampling techniques previously developed either for pure market portfolio models or for pure credit portfolio models can be successfully applied to integrated market and credit portfolio models. Specific problems which arise in this context are discussed. The effectiveness of these techniques is tested by numerical experiments for linear and non-linear portfolios.     

基于随机市场需求的供应链融资模式研究

传统供应链融资模型大都在线性市场需求情形下分析零售商的商业信用、债权融资等内外部融资模式。本文同时了考虑零售商的股权融资、债权融资以及商业信用融资模式, 并引入随机市场需求因素, 针对一个供应商和两个具有资金约束零售商组成的两级供应链, 分析债权股权融资比例、商业信用等因素对零售商融资策略的影响, 并构建基于随机市场需求的融资模型;进一步, 利用数值示例和敏感性分析对此融资模型进行深入探讨。研究发现:当债权融资比例小于某临界值时, 零售商债权融资比例与订购量正相关, 反之债权融资比例与订购量负相关;对于一个服从均匀分布函数的随机市场需求而言, 若供应链采用外部融资模式, 那么随着其债权融资比例的增大, 利润将逐渐增加;若零售商采用商业信用融资模式, 那么其融资利率与利润负相关。相关研究结论对于供应链上中小企业融资模式的选择具有重要理论指导意义和实际引用价值。     

Dynamic Hedging of Portfolio Credit Risk in a Markov Copula Model

We devise a bottom-up dynamic model of portfolio credit risk where instantaneous contagion is represented by the possibility of simultaneous defaults. Due to a Markovian copula nature of the model, calibration of marginals and dependence parameters can be performed separately using a two-step procedure, much like in a standard static copula setup. In this sense this solves the bottom-up top-down puzzle which the CDO industry had been trying to do for a long time. This model can be used for any dynamic portfolio credit risk issue, such as dynamic hedging of CDOs by CDSs, or CVA computations on credit portfolios.     

An integrated pricing model for defaultable loans and bonds

In recent years, credit risk has played a key role in risk management issues. Practitioners, academics and regulators have been fully involved in the process of developing, studying and analysing credit risk models in order to find the elements which characterize a sound risk management system. In this paper we present an integrated model, based on a reduced pricing approach, for market and credit risk. Its main features are those of being mark to market and that the spread term structure by rating class is contingent on the seniority of debt within an arbitrage-free framework. We introduce issues such as, the integration of market and credit risk, the use of stochastic recovery rates and recovery by seniority. Moreover, we will characterize default risk by estimating migration risk through a “mortality rate”, actuarial-based, approach. The resultant probabilities will be the base for determining multi-period risk-neutral transition probability that allow pricing of risky debt in the trading and banking book.