MASTER THESIS in MATHEMATICS / APPLIED MATHEMATICS Hedging Interest Rate Derivatives (Evidence from Swaptions) in a Negative
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MASTER THESIS IN MATHEMATICS / APPLIED MATHEMATICS Hedging Interest Rate Derivatives (Evidence from Swaptions) in a Negative Interest Rate Environment: A comparative analysis of Lognormal and Normal Model by Shadrack Lutembeka Masterarbete i matematik / tillämpad matematik DIVISION OF APPLIED MATHEMATICS MÄLARDALEN UNIVERSITY SE-721 23 VÄSTERÅS, SWEDEN Master thesis in mathematics / applied mathematics Date: 2017-01-19 Project name: Hedging Interest Rate Derivatives (Evidence from Swaptions) in a Negative Interest Rate En- vironment: A comparative analysis of Lognormal and Normal Model Author: Shadrack Lutembeka Supervisor(s): Jan Röman and Richard Bonner Reviewer: Anatoliy Malyarenko Examiner: Linus Carlsson Comprising: 30 ECTS credits Abstract This thesis is about hedging interest rate derivatives in a negative interest rate environment. The main focus is on doing a comparative analysis on how risk varies between Lognormal and Normal models. This because Lognormal models do not work in the negative interest rate since they do not allow negative values, hence there is a need of using Normal models. The use of different models will yield identical price but different hedges. In order to study this we looked at the case of Swaptions and Swaps as an example of interest rate derivatives. To study risk in these two models we employed the method of risk matrices to measure and report risk. We created various risk matrices for both Black model and Normal Black model which included the price matrices, Delta and Vega matrices to study how Swaptions and Swaps with different maturities are sensitive to changes in different parameters. We also plotted how Delta and Vega vary between the two models. Acknowledgements First and foremost I would like to thank God for always taking care of me. Secondly I would like to convey my special thanks to the Swedish Institute (SI) for awarding me a full scholar- ship to study the masters program Financial Engineering at Mäladalen University. Thirdly i would like to convey my sincere thanks to my supervisor Jan Röman who invested alot of his time and efforts to ensure that this thesis becomes a success, am truly grateful. I wouldn’t also forget my other supervisor, Richard Bonner for his continuous and prompt guidance during the writing of this thesis. To my dear parents who have been so supportive since day one that I set foot at the nursery school. To my siblings; Lilian, Meshack, Godfrey and Gladness for their continuous support throughout this journey. Last but not least are my dear friends and family, Polite Mpofu, Erick Momamnyi, James Okemwa, Oliver Grace, Kakta Mpofu and Mahalet Haile Selassie for always being there throughout this journey. 1 Contents 1 Introduction5 1.1 Negative Interest Rates Environment......................5 1.2 Motivation for Negative Interest Rate Policies.................6 1.3 Motivation and Problem Formulation......................7 1.3.1 Motivation...............................7 1.3.2 Problem Formulation..........................8 1.4 Understanding Interest Rates..........................9 1.5 Overview and Outline.............................. 12 2 Lognormal Model versus Normal Model 13 2.1 Pricing Models................................. 13 2.2 Log Normal Models............................... 14 2.2.1 Black’s model............................. 15 2.2.2 The Constant Elasticity of Variance (CEV) Model........... 17 2.2.3 The Stochastic Alpha Beta Rho (SABR) Model............ 18 2.3 Normal Models................................. 19 2.3.1 Bachelier’s Model........................... 20 2.3.2 Normal SABR Model......................... 20 3 Hedging Parameters 22 3.1 Greeks in Black-Scholes............................ 22 3.2 Greeks in Other Models............................. 26 3.2.1 Black Model.............................. 26 3.2.2 Normal Model............................. 27 2 3.2.3 SABR Model.............................. 28 3.3 Hedging Strategies............................... 29 3.3.1 Risk Matrices.............................. 31 4 Interest Rate Derivatives 32 4.1 Derivatives................................... 32 4.2 Interest Rate Derivatives............................ 33 4.2.1 Forward rate agreement (FRA)..................... 33 4.2.2 Caps.................................. 35 4.2.3 Floors.................................. 36 4.2.4 Bond Options.............................. 37 4.2.5 Interest Rate Swap........................... 37 4.2.6 Swaption................................ 41 5 Implementation 44 5.1 Bootstrapping a Swap Curve.......................... 44 5.2 Premium and Risk Measures Calculations................... 45 5.2.1 Plotting Delta and Vega in Black and Normal Black Model...... 46 5.3 Risk Matrices for Swaptions and Swaps at Different Maturities........ 48 5.3.1 Price Sensitivity............................ 48 5.3.2 Delta and Vega Sensitivity....................... 49 6 Conclusion 51 7 Notes on fulfillment of Thesis objectives 52 Bibliography 54 A More mathematics 56 A.1 Singular Pertubation Technique......................... 56 A.2 Solution to Black Model............................ 57 B APPENDIX B 59 B.1 Extract of VBA Program Codes........................ 59 3 B.2 Risk Matrices for Swaptions and Swaps with Different Maturities...... 61 4 Chapter 1 Introduction 1.1 Negative Interest Rates Environment In a normal world, one would expect that a lender to receive from a borrower a rate on the amount borrowed. It is also expected that when one deposits money in the bank, he would expect to get back some form of interest on his deposit. However, when we have a situation where lenders have to pay borrowers for lending from them or when depositors are charged for keeping their money with the bank instead of receiving an interest income, we have what we call "negative interest rate". One could argue that interest rates were modelled to be positive to compensate a lender for undertaking the risk of borrowing. Most of economic theory fact that nominal interest rates should have a zero lower bound. In 1995, Black(1995) stated explicitly in his paper that it is possible to have negative real interest rate but we cannot have the negative nominal short rate. After almost twenty years we question if Black’s assumption was correct. In the current negative interest rate environment with around $ 13.5 trillion of negative-yielding bonds as reported by financial times in August 20161 central banks such as the European Central Bank have cut the deposit rate to below zero per cent. As a result, instead of paying interest to the banks or financial institutions that deposits their excess reserves to the central bank, the central bank taxes these deposits. As irrational as this concept may seem to be, the main idea behind it is to discourage the banks from parking the balances at the central bank, instead increase their lending or investments. However negative nominal interest rates is not a completely new concept. One could trace negative nominal interest rates back in the 19th century when "Gesell Tax" was introduced to overcome the zero-lower-bound on nominal interest rates Menner(2011). Similary in the 1970s the Swiss National Bank also experimented with negative rates to control capital inflows in a bid to prevent the Swiss Franc from appreciating. Looking with fresh eyes, in the past few years, we have witnessed the changes of interest rate environment. The global financial system 1This information was retrieved from Financial Times website: https://www.ft.com/content/973b6060-60ce- 11e6-ae3f-77baadeb1c93 on 12-14-2016 5 has been venturing further into the whole new world of negative interest rates. Between 2014 and 2016, five central banks namely, European Central Bank (ECB), Sveriges Riksbank (SR), Bank of Japan, Denmark National bank (DN) and the Swiss National Bank (SNB) decided to implement negative rate policy. As it can be seen from Figure 1.1 below 2. ECB was the first bank to decrease their interest rates to below zero in June 2014, since then the rate has been dividing deeper below zero. Figure 1.1: This figure shows the European Central bank’s interest rates from 2008 until early 2016. 1.2 Motivation for Negative Interest Rate Policies There are different motivations for implementing negative interest rate policy. Bech and Malk- hozov(2016) mention different reasons for the implementation of the negative interest rate policy in Europe. One of the major reason to implement negative rate policy has been to boost the economy and to raise inflation which is currently below zero. The other reason is to pre- vent high rising of the currency. By lowering negative interest rates, investors are discouraged by banks from buying the local currency hence preventing its value from rising up. Table 13 below summarizes the rationale behind implementation of negative rate policy by different banks in Europe. 2The figure is extracted from https://www.bloomberg.com/quicktake/negative-interest-rates 3The table is extracted from Jackson(2015). In the table; bp stands for basis points and DKK is the ISO code for Danish krone 6 1.3 Motivation and Problem Formulation In this section, we discuss the motivation behind carrying out this research and highlight why studying risk in the negative interest rate environment is important. 1.3.1 Motivation After having looked at the current negative interest environment in the world (especially in Europe), it is important to now look at how all this has an impact on the interest rate derivatives traded in the market. There is need to incorporate this new reality of negative interest rates in our models and in our volatility assumptions. 7 The need to change models Black’s model has been used as the standard model in the market to price interest rate de- rivatives. As will be discussed later, the key feature of this model is that it assumes that the forward rates are lognormally distributed. This assumption allows the Black model to work only with positive values, the Black model valuation formula is constructed in such a way that it rejects any negative values. It is then clear that in negative interest rate environment where we have negative values we cannot use the standard models like Black model to price and hedge interest rate derivatives.