Doctor of Philosophy
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Study of Scalars and Fermions in Models Beyond the Standard Model Deepanjali Goswami A thesis submitted for the degree of Doctor of Philosophy Department of Physics Indian Institute of Technology Guwahati Guwahati 781039, India June 2019 TH-2130_136121013 TH-2130_136121013 Study of Scalars and Fermions in Models Beyond the Standard Model Deepanjali Goswami A thesis submitted for the degree of Doctor of Philosophy Supervisor: Prof. Poulose Poulose Department of Physics Indian Institute of Technology Guwahati Guwahati 781039, India June 2019 TH-2130_136121013 TH-2130_136121013 Declaration The work contained in the thesis entitled \Study of Scalars and Fermions in Models Beyond the Standard Model" has been carried out at the Department of Physics, Indian Institute of Technology Guwahati, India by me under the supervision of Prof. Poulose Poulose. The material of this thesis has not been submitted elsewhere for any other degree. Works presented in the thesis are all my own unless referenced to the contrary in the thesis. Date: (Deepanjali Goswami) June, 2019 Department of Physics Indian Institute of Technology Guwahati Guwahati - 781039, India v TH-2130_136121013 TH-2130_136121013 Disclaimer The bibliography included in this thesis is, by no means complete but contains the ones which are consulted thoroughly by me. I apologize for inadvertently missing out some of the research papers, review articles and other scientific documents pertaining to the focus of this thesis which should also have been cited. vii TH-2130_136121013 TH-2130_136121013 Prof. Poulose Poulose Department of Physics Indian Institute of Technology Guwahati Guwahati-781039, INDIA Email: [email protected] Certificate It is to certify that the work contained in the thesis entitled \Study of Scalars and Fermions in Models Beyond the Standard Model " by Ms. Deepanjali Goswami (Roll No -136121013), a PhD student in the Department of Physics, Indian Institute of Technology Guwahati is carried out under my supervision and has not been submitted elsewhere for the award of any degree. Date: Poulose Poulose (Professor) TH-2130_136121013 TH-2130_136121013 Dedicated to My parents and motherland... TH-2130_136121013 TH-2130_136121013 Acknowledgements I would like to express my gratitude, respect and appreciation to the Almighty before writing this page! This page takes me to the onset of my deep involvement of pursuing PhD degree which begins from the picturesque and the utmost naturally beautiful campus, my beloved institution, to whom I would like to thank for giving me an opportunity to be a part of it with one of the most prestigious affiliations, the Indian Institute of Technology Guwahati. I feel myself very fortunate and honoured to get such an institute to spend couple of years with wonderful people around, surrounded by scenic beauty of mother nature. The presence of mighty Brahmaputra, the beautiful hills around the campus, with its lakes inside and flowers serve as a splendid feat to make it even more exquisite. Its collective contribution has inculcated in me slowly and silently, and immensely helped me in my learning process throughout this journey. Having said that, now firstly and foremost, I would like to express my indebtful grat- itude toward my thesis supervisor Prof. Poulose Poulose for giving me an opportunity to work under his esteemed and profound guidance. His continuous support, inspiration, constant motivation, encouragement and his immense knowledge have contributed towards successful completion of my PhD research work. He has always been motivating me to learn the deeper aspects of physics and his inspirational words immensely helped me to get the high spirit to do the research and to be able to move over all the ups and downs of research life. Alongwith, I would like to thank Ms. Stavelin Ma'am for her inspirational words and their two adorable kids Hasvid and Onella for sharing many beautiful moments with me. xiii TH-2130_136121013 xiv Acknowledgements I would also like to express my sincere gratitude to my doctoral committee members: Dr. Arunansu Sil (Chairman), Dr. Udit Raha, and Dr. Soumitra Nandi, for reviewing my yearly progress with their valuable suggestions and for giving me their insightful comments and encouragement, and also for their positive critics which aspired in me to widen my research process from various prospectives. I would also like to thank, all former and current, Head of Department of Physics (Prof. Saurabh Basu, Prof. Poulose Poulose and Prof. Subhradip Ghosh), for their support and providing me various departmental facilities. It is my pleasure to thank all the faculty members of the Department of Physics, IIT Guwahati for their support and help during this journey. Specially, I would like to express my grateful thanks to Dr. Subhaditya Bhattacharya, Dr. Tarak Nath Dey, Prof. Sunil K Khijwania, Dr. Debaprasad Maity, Dr. Malay Kumar Nandy, Prof. Perumal Alagarsamy, Prof. Girish Sampath Setlur. I thank all scientific officers of Department of Physics, IITG, specially Dr. Sidananda Sarma for his motivational words and Mr. Basab Bijoy Purkayastha for his continuous support and all time help at any emergency situation with all my technical issues. I would also like to acknowledge my department office staff members for their kind help. It is my honour to reserve my special thanks to Prof. Benjamin Fuks, Dr. Debasish Borah for providing me an opportunity to work and having wonderful experience of learning while collaborating with them, I have learned several analysis techniques of my research work from Prof Fuks and my knowledge treasure has been benefitted immensely with the discussions I had with Dr. Debasish Borah. I greatly owe a lot to Prof Daniel Jeans for providing me valuable opportunity to work with him at KEK, Japan. I would like to sincerely thank him, as with him I learned the basics of the ILC study. It is my privilege to thank all my teachers, starting from my school days, whose efforts and blessings have helped me in reaching to the current position. The person who holds a special place in my heart is my father cum my teacher Prof D. D. Goswami, for teaching me motivational lesson of life and to pursue my carrier in physics. I would remain in- debted for his uncountable contribution in my life as a result of which I could achieve upto this stage. I also express my grateful thanks to my brother cum teacher Dr. Umananda Dev Goswami, for his help in making me wade through the challenging times of my life TH-2130_136121013 Acknowledgements and pursue the research. I am also highly thankful to Prof Bipul Bhuyan for his help and providing me a working space in a conducive ambience of his High Energy Physics Laboratory. He was also very kind to allow me to access his HEP cluster to carry out the necessary high speed computation for my research work. I am also thankful to him for having several insightful discussions about current physics scenarios in experimental high energy physics. I extend my acknowledgement to DAE-BRNS, Govt of India for the research fellow- ship, International Travel Support under DST, Govt. of India for presenting a paper at the APS April Meeting 2016 held at Utah, USA. I also acknowledge Govt. of Japan, for selecting me for the Invitation Fellowship Program for Young Women Researchers in Asia Pacific Countries under Athena Program to visit KEK, Japan in January 2019. I thank my research group friends: Dr. Satendra Kumar, Dr. Biswaranjan Das, Dr. Shibananda Sahoo, Subhasish Behera, Dr. Rashidul Islam, Suresh Chand and Sreemanti Chakraborti for their help and many fruitful discussions. I would also like to thank my senior research fellow members Dr. Deepanwita Dutta, Dr. Biswajit Karmakar and lab mates and friends Dr. Kamal Jyoti Nath, Maharnab, Dibyajyoti, Devender, Jyotirmoi, Shubhangi, Sunayana and Pulak for their kind help. A special thanks goes to my beloved friends Dr. Chandita Baruah, Dr. Prahlad Baruah, Niharika Baruah, Biju Bharali and Dr. Sushma Chityala for sharing the beautiful moments in the lovely IITG campus and always staying by my side in all my sad and happy times. The memories collected with them are as precious as they are. This acknowledgement would remain incomplete without the mention of the love, the care, the hard work and the sacrifice of my ancestors, my grandparents, my beloved parents, my relatives and Guruji in bringing me up and also the utmost affection, given by my entire family, specially my sister Dr. Rupanjali Goswami and brother in law Mr. Nripen Mahanta for their constant support and keeping the faith in me to allow me to do what I like. I feel myself to be extremely fortunate to gain such unimaginable strength from Mummyji, my sisters Dr. Neelima Yadav, Teshma Di and Anamika, for supporting me unconditionally, and any degree of acknowledgment to the God's gifts: Dr. Nitin Yadav, TH-2130_136121013 xvi Acknowledgements Krishna, Raj, Ruchi, Lucky, Kanha, Dolcy, would somewhere, definitely, leave in me a void of ungratefulness. June, 2019 Deepanjali Goswami TH-2130_136121013 Abstract The Standard Model (SM) of particle physics is well established with the discovery of the Higgs boson by the independent experiments, ATLAS and CMS at LHC in 2012. The properties of the discovered Higgs boson is very similar to the proposed one in the SM and the discovery is considered as a remarkable success of this model. Inspite of this success, many experimental evidences provide hints of some fundamental issues; mainly absence of dark matter (DM), non-zero neutrino mass and hierarchy problem, which shows that the SM is not a complete theory. A possible way out of this situation is to look beyond the SM(BSM) to resolve these issues by accommodating new particles in the spectrum or extending the gauge sector of the SM. Out of many attractive proposals of BSM, models governing seesaw mechanism could explain the non-zero masses of neutrinos.