Cosmic String Searches in New Observational Windows Rebecca Jean Danos Department of Physics McGill University Montreal, Quebec February 2011 A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy Doctor of Philosophy c Rebecca Jean Danos, 2011. All rights reserved Abstract Placing observational limits on cosmic strings would provide important con- firmation of or constraints on early universe models. Cosmic strings imprint the cosmic microwave background (CMB) with a distinct position space signa- ture, leaving line discontinuities in the temperature maps due to a combination of gravitational lensing and the Doppler effect. To improve theoretical obser- vational constraints, I wrote sky map simulations with and without cosmic strings, edge detection and counting algorithms, and programs to differentiate statistically between the ambient edges due to the inflationary background and the string signals. Our application of position space algorithms, specifically the Canny edge detection algorithm, was highly successful and allowed us to establish improved limits, by more than an order of magnitude, on the con- tribution of cosmic strings to the total fluctuation spectrum from simulated data. We extended our analysis of the Canny algorithm to distinguish between abelian cosmic strings and cosmic superstrings through the presence of three- string junctions in cosmic superstring maps. To this end, I wrote the first simulations of maps with junctions and found a disparity in the density of edges in maps of string networks with and without junctions. This work re- sulted in a statistic to differentiate between different cosmic string models including string theory models and models with different numbers of cosmic strings. I also modeled the position space polarization signal induced by cosmic string wakes. Due to the gravity of a moving string, matter falls into over- dense two dimensional sheets of matter, wakes, behind the string. As photons propagate through the wakes, they encounter this overdensity of ionized mat- ter which can polarize them. In our work we placed the first limits on the CMB polarization signature of cosmic strings including their signature non- linear structures, wakes, and found they would produce an observable signal ii when used in combination with an algorithm such as the Canny algorithm. The cosmic string wakes lead to a gradient in the intensity of polarization in the shape of the wake, greater at earlier positions of the string. The overdense wakes produced by strings provide more opportunity for the 21 cm hydrogen spin flip as well, so we found that cosmic strings wakes can be observed as three dimensional wedges in maps of 21 cm radiation absorption. Our paper is among the first to study the cosmic string signature in 21 cm and the first to examine the influence of wakes on the 21 cm signal. iii R´esum´e La mise en place de limites d’observation sur les cordes cosmiques perme- ttraient de confirmer, ou `atout le moins de contraindre de fa¸con importante, les pr´esents mod`eles de l’Univers primordial. Les cordes cosmiques impr`egnent le fond diffus cosmologique (ou CMB) d’une signature distincte dans l’espace, sous forme de discontinuit´es lin´eiques dans les cartes de temp´eratures. Ces derni`eres sont dues `aune combinaison des effets de lentilles gravitationnelles et de l’effet Doppler. Afin d’am´eliorer les contraintes observationnelles th´eoriques, j’ai ´ecris des simulations de cartes du ciel avec et sans cordes cosmiques, des algorithmes de d´etection et de comptages des lignes de discontinuit´e, ainsi que des programmes permettant de distinguer de fa¸con statistique les lignes de dis- continuit´eproduites naturellement dans le contexte de l’inflation cosmique de celles dues `ala pr´esence de cordes cosmiques. L’application d’algorithmes dans le domaine spatial (par opposition au domaine des harmoniques sph´eriques), en particulier l’application de l’algorithme de d´etection de discontinuit´es lin´eiques Canny, fut tr`es r´eussie et nous a permis d’´etablir des limites am´elior´ees de plus d’un ordre de grandeur sur la contribution des cordes cosmiques `al’ensemble du spectre de fluctuations pour les donn´ees simul´ees. Nous avons ´etendu notre analyse utilisant l’algorithme Canny pour nous permettre de distinguer les cordes cosmiques ab´eliennes des supercordes cos- miques en analysant la pr´esence de jonctions de trois cordes dans les cartes de supercordes cosmiques. A` cette fin, j’ai ´ecris les premi´eres simulations de cartes incorporant ces jonctions et ai constat´eune disparit´edans la densit´e de lignes de discontinuit´ed´etect´ee dans les cartes de r´eseaux de cordes avec et sans jonctions. Ce travail m’a permis d’´elaborer un mod`ele statistique per- mettant de diff´erencier les diff´erents mod`eles de cordes cosmiques, y compris les mod`eles provenant de la th´eorie des cordes et les mod`eles avec diff´erents nombres de cordes cosmiques. J’ai aussi mod´elis´e, dans le domaine spatial, le signal de polarisation induit par les sillages de cordes cosmiques. En raison de iv la g´eom´etrie sp´ecifique de son champs gravitationnel, une corde cosmique en mouvement cause l’accr´etion de mati`ere dans des r´egions de surdensit´ebidi- mentionnelles, ou sillages, derri`ere elle. Lorsque des photons se propagent `a travers ces sillages, ils peuvent ˆetre polaris´es par leur rencontre avec la r´egion de surdensit´ede mati´ere ionis´ee qui s’y trouve. Par notre travail, nous avons impos´eles premi`eres limites sur la signature possible laiss´ee dans le champs de polarisation du CMB, en incluant les effets de leur structures non-lin´eaires, c’est-`a-dire de leurs sillons, et trouv´eque ces derni`eres produiraient un signal d´etectable lorsqu’utilis´ees de concert avec un algorithme tel que l’algorithme Canny. Les sillages d’une corde cosmique donnent naissance `aun gradient d’intensit´e dans le spectre de polarisation pr´esent dans la structure des sillages, la polar- isation ´etant plus importante aux points les plus recul´es dans l’histoire du d´eplacement de la corde. Les zones de surdensit´eproduites par les sillages des cordes donnent ´egalement lieu `aune gamme d’opportunit´es concernant la raie d’´emission `a21 cm de l’hydrog`ene. Ainsi, nous avons d´ecouvert que les sil- lages de cordes pourraient ˆetre observ´esous la forme de prismes triangulaires tridimensionnels dans les cartes d’absorption de la raie `a 21 cm. Notre article est parmis les premiers `a´etudier la signature des cordes cosmiques dans le spectre d’absorption de la raie `a21 cm, et est le premier `aexaminer l’influence possible des sillages sur ce dernier. v Dedication This thesis is dedicated to Andrew with all my love vi Acknowledgements I would like to thank with all my heart all of the people who have of- fered their support of me and made this long journey through graduate school possible. First and foremost I would like to thank my husband, Andrew R. Frey, for all of his unceasing support in every possible way for which I cannot express enough my eternal gratitude. Without his belief in me and nurture, completing this degree would be but a dream. Next I would like to thank with all my heart my co-advisors Robert Brandenberger and Keshav Dasgupta for all of their support, advice, discussions, and scientific and personal guidance. I am particularly indebted to the inspired guidance of Robert Brandenberger without which I would not have been able to complete this thesis; I am very grateful for his careful attention and insightful discussions. I am also indebted to Keshav Dasgupta for his understanding and caring encouragement. I would like to thank those members of the McGill University physics de- partment who made my tenure here memorable and meaningful including Jim Cline, Eddie Del Campo, Fang Chen, Hong Guo, Rhiannon Gwyn, Sangyong Jeon, Alex and Fergus Maloney, Paul Mercure, Guy Moore, Marcus Tassler, Tracy Webb, and Wang Yi. I would also like to thank Andrew Stewart and Stephen Amsel for useful discussions. I would especially like to thank Gil Holder and Matt Dobbs for many pedagogical and helpful discussions and for insightful comments on sections of my dissertation. I would also like to thank Alex van Engelen for useful discussions and comments on sections of my dis- sertation. I am particularly grateful to Laurence Perreault Levasseur for her careful translation of my abstract into French and useful discussions. There have been many people who believed in me when I did not, and they deserve my heartfelt thanks. I would like to express my deepest gratitude to Norman Hoffman and Elaine Ransom-Hodges who have offered tremendous support and unending encouragement. I would also like to deeply thank my music teachers Eva Csarnay and Genevieve Levesque who taught me much vii about the art of living and believing in myself while I’ve been at McGill which has inspired my scientific endeavors as well as my musical ones. I also have numerous friends and family who contributed to my experience at McGill University. I would like to thank Aunt Ginny McCloskey for all her optimism and helpful phone conversations, my dear friend Sugumi Kanno for all her caring encouragement and for serving as a mentor and big sister to me. I would also like to thank deeply my UCLA advisor Per Kraus and my internship advisor Ue-Li Pen for all of their support of my career, posi- tive encouragement, and physical insight in stimulating discussions during my tenure at McGill. I would also like to thank my dear friends Anupam Mazum- dar, Jonathan McDowell, Natasha Lepore, Judy Wong, and Richard Scalzo for their generous, spirited support and encouragement particularly in challenging times.