Cosmic Rays from Cosmic Strings with Condensates (2009)
We re-visit the production of cosmic rays by cusps on cosmic strings. If a scalar field (``Higgs'') has a linear interaction with the string world-sheet, such as would occur if there is a bosonic...
Aharonov-Bohm Radiation (2009)
Jones-Smith, Katherine, Mathur, Harsh, Vachaspati, Tanmay
A solenoid oscillating in vacuum will pair produce charged particles due to the Aharonov-Bohm (AB) interaction. We calculate the radiation pattern and power emitted for charged scalar particles. We...
Dutta, Sourish, Vachaspati, Tanmay
If the observed dark energy is a cosmological constant, the canonical state of the universe is de Sitter spacetime. In such a spacetime, quantum fluctuations that violate the null energy condition...
Recent astrophysical observations have motivated novel theoretical models of the dark matter sector. A class of such models predicts the existence of GeV scale cosmic strings that communicate with...
Cosmology of Bifundamental Fields (2008)
If a field theory contains gauged, non-Abelian, bi-fundamental fields i.e. fields that are charged under two separate non-Abelian gauge groups, the transition from a deconfined phase to a hadronic...
Formation of Non-Abelian Monopoles Connected by Strings (2008)
Ng, Yifung, Kibble, T. W. B., Vachaspati, Tanmay
We study the formation of monopoles and strings in a model where SU(3) is spontaneously broken to U(2)=[SU(2)\times U(1)]/\ZZ_2, and then to U(1). The first symmetry breaking generates monopoles with...
Creating kinks from particles (2008)
Dutta, Sourish, Steer, D. A., Vachaspati, Tanmay
We study the creation of solitons from particles, using the $\lambda \phi^4$ model as a prototype. We consider the scattering of small, identical, wave pulses, that are equivalent to a sequence of...
Magnetic Fields in the Aftermath of Phase Transitions (2008)
The COSLAB effort has focussed on the formation of topological defects during phase transitions. Yet there is another potentially interesting signature of cosmological phase transitions, which also...
Microlensing by cosmic strings (2008)
Kuijken, Konrad, Siemens, Xavier, Vachaspati, Tanmay
We consider the signature and detectability of gravitational microlensing of distant quasars by cosmic strings. Because of the simple image configuration such events will have a characteristic...
Cosmic Sparks from Superconducting Strings (2008)
We investigate cosmic sparks from cusps on superconducting cosmic strings in light of the recently discovered millisecond radio burst by Lorimer et al [1]. We find that the observed duration,...
Helical Magnetic Fields from Sphaleron Decay and Baryogenesis (2008)
Copi, Craig J., Ferrer, Francesc, Vachaspati, Tanmay, Achucarro, Ana
Many models of baryogenesis rely on anomalous particle physics processes to give baryon number violation. By numerically evolving the electroweak equations on a lattice, we show that baryogenesis in...
Schrodinger Picture of Quantum Gravitational Collapse (2007)
The functional Schrodinger equation is used to study the quantum collapse of a gravitating, spherical domain wall and a massless scalar field coupled to the metric. The approach automatically...
Fermions on one or fewer Kinks (2007)
Chu, Yi-Zen, Vachaspati, Tanmay
We find the full spectrum of fermion bound states on a Z_2 kink. In addition to the zero mode, there are int[2 m_f/m_s] bound states, where m_f is the fermion and m_s the scalar mass. We also study...
Quantized Non-Abelian Monopoles on S^3 (2007)
Maor, Irit, Mathur, Harsh, Vachaspati, Tanmay
A possible electric-magnetic duality suggests that the confinement of non-Abelian electric charges manifests itself as a perturbative quantum effect for the dual magnetic charges. Motivated by this...
Microlensing by Cosmic Strings (2007)
Kuijken, Konrad, Siemens, Xavier, Vachaspati, Tanmay
We consider the signature and detectability of gravitational microlensing of distant quasars by cosmic strings. Because of the simple image configuration such events will have a characteristic light...
Black Stars and Gamma Ray Bursts (2007)
Stars that are collapsing toward forming a black hole but are frozen near the Schwarzschild horizon are termed ``black stars''. Collisions of black stars, in contrast to black hole collisions, may be...
On Constructing Baby Universes and Black Holes (2007)
The creation of spacetimes with horizons is discussed, focussing on baby universes and black holes as examples. There is a complex interplay of quantum theory and General Relativity in both cases,...
Quantum Radiation from Quantum Gravitational Collapse (2007)
Vachaspati, Tanmay, Stojkovic, Dejan
We study quantum radiation emitted during the collapse of a quantized, gravitating, spherical domain wall. The amount of radiation emitted during collapse now depends on the wavefunction of the...
Observation of Incipient Black Holes and the Information Loss Problem (2006)
Vachaspati, Tanmay, Stojkovic, Dejan, Krauss, Lawrence M.
We study the formation of black holes by spherical domain wall collapse as seen by an asymptotic observer, using the functional Schrodinger formalism. To explore what signals such observers will see,...
Light superconducting strings in the Galaxy (2006)
Ferrer, Francesc, Vachaspati, Tanmay
Observations of the Milky Way by the SPI/INTEGRAL satellite have confirmed the presence of a strong 511 KeV gamma-ray line emission from the bulge, which require an intense source of positrons in the...
Intercommutation of Semilocal Strings and Skyrmions (2006)
Laguna, Pablo, Natchu, Vishnu, Matzner, Richard A., Vachaspati, Tanmay
We study the intercommuting of semilocal strings and Skyrmions, for a wide range of internal parameters, velocities and intersection angles by numerically evolving the equations of motion. We find...
Zero modes on cosmic strings in an external magnetic field (2006)
Ferrer, Francesc, Mathur, Harsh, Vachaspati, Tanmay, Starkman, Glenn D.
A classical analysis suggests that an external magnetic field can cause trajectories of charge carriers on a superconducting domain wall or cosmic string to bend, thus expelling charge carriers with...
On the Detection of Magnetic Helicity (2005)
Kahniashvili, Tina, Vachaspati, Tanmay
Magnetic fields in various astrophysical settings may be helical and, in the cosmological context, may provide a measure of primordial CP violation during baryogenesis. Yet it is difficult, even in...
511 KeV photons from superconducting cosmic strings (2005)
Ferrer, Francesc, Vachaspati, Tanmay
We show that a tangle of light superconducting strings in the Milky Way could be the source of the observed 511 KeV emission from electron-positron annihilation in the Galactic bulge. The scenario...
Islands in the Lambda-sea: An alternative cosmological model (2005)
Dutta, Sourish, Vachaspati, Tanmay
We propose an alternate cosmological model in which our observable universe is an island in a cosmological constant sea. Initially the universe is filled with cosmological constant of the currently...
Distribution of Singularities in the Cosmic Microwave Background Polarization (2004)
Huterer, Dragan, Vachaspati, Tanmay
The polarization of the cosmic microwave background radiation will have a distribution of singularities and anti-singularities, points where the polarization vanishes for topological reasons. The...
Spontaneous formation of domain wall lattices in two spatial dimensions (2004)
Antunes, Nuno D., Vachaspati, Tanmay
We show that the process of spontaneous symmetry breaking can trap a field theoretic system in a highly non-trivial state containing a lattice of domain walls. In one large compact space dimension, a...
Cosmic Problems for Condensed Matter Experiment (2004)
Condensed matter analogs of the cosmological environment have raised the hope that laboratory experiments can be done to test theoretical ideas in cosmology. I will describe Unruh's sonic analog of a...
Topology in the Little Higgs Models (2004)
Trodden, Mark, Vachaspati, Tanmay
We investigate the implications of the nontrivial vacuum structure of little Higgs models. In particular, focusing on the littlest Higgs model, we demonstrate the existence of three types of...
Propagating phase boundaries as sonic horizons (2003)
If certain conditions are met, a propagating phase boundary can be a sonic horizon. Sonic Hawking radiation from such a phase boundary is expected in the quantum theory. The Hawking temperature for...
Forecasting Cosmic Doomsday from CMB/LSS Cross-Correlations (2003)
Garriga, Jaume, Pogosian, Levon, Vachaspati, Tanmay
A broad class of dark energy models, which have been proposed in attempts at solving the cosmological constant problems, predict a late time variation of the equation of state with redshift. The...
Reconstruction of field theory from excitation spectra of defects (2003)
We show how to reconstruct a field theory from the spectrum of bound states on a topological defect. We apply our recipe to the case of kinks in 1+1 dimensions with one or two bound states. Our...
On formation of domain wall lattices (2003)
Antunes, Nuno D., Pogosian, Levon, Vachaspati, Tanmay
We study the formation of domain walls in a phase transition in which an S_5\times Z_2 symmetry is spontaneously broken to S_3\times S_2. In one compact spatial dimension we observe the formation of...
Eternal inflation and energy conditions in de Sitter spacetime (2003)
Eternal inflation is shown to require violations of the Null Energy Condition (NEC) on superhorizon scales. With light scalar fields as the matter sources in a de Sitter background, there can be no...
Gravitational Lensing by Cosmic Strings in the Era of Wide-Field Surveys (2003)
Huterer, Dragan, Vachaspati, Tanmay
Motivated by the recent claim for gravitational lensing by a cosmic string, we reinvestigate the probability of finding such an event with upcoming wide-field surveys. If an observed lensing event is...
Topological properties of the Cosmic Microwave Background polarization map (2003)
Vachaspati, Tanmay, Lue, Arthur
Rapid progress has been made in observations of the temperature anisotropies of the Cosmic Microwave Background (CMB). These observations have enabled cosmologists to characterize the state of the...
Symmetries within domain walls (2003)
The comparison of symmetries in the interior and the exterior of a domain wall is relevant when discussing the correspondence between domain walls and branes, and also when studying the interaction...
A post-WMAP perspective on inflation (2003)
Lue, Arthur, Starkman, Glenn D., Vachaspati, Tanmay
Recent results from the Wilkinson Microwave Anisotropy Probe have been called a corroboration, or even a confirmation, of inflation. Yet, the results include features that require, at least, a...
I describe domain walls and domain wall lattices in non-Abelian models.
Pogosian, Levon, Vachaspati, Tanmay
We construct lattices with alternating kinks and anti-kinks. The lattice is shown to be stable in certain models. We consider the forces between kinks and antikinks and find that the lattice dynamics...
Signatures of primordial helicity in the CMBR (2002)
Pogosian, Levon, Vachaspati, Tanmay, Winitzki, Serge
We have studied ways in which helical primordial magnetic fields could be constrained by measurements of the cosmic microwave background radiation (CMBR). If there were helical flows in the...
Triplication of SU(5) monopoles (2002)
Pogosian, Levon, Steer, Daniele A., Vachaspati, Tanmay
We investigate all spherically symmetric fundamental monopole solutions with fixed topological charge in the SU(5) --> SU(3)xSU(2)xU(1)/Z_3xZ_2 symmetry breaking. We find that there is three-fold...
Bound states in bottomless potentials (2002)
We consider classical and quantum dynamics on potentials that are asymptotically unbounded from below. By explicit construction we find that quantum bound states can exist in certain bottomless...
Band structure in classical field theory (2002)
Salem, Michael, Vachaspati, Tanmay
Stability and instability bands in classical mechanics are well-studied in connection with systems such as described by the Mathieu equation. We examine whether such band structure can arise in...
Signatures of kinetic and magnetic helicity in the CMBR (2001)
Pogosian, Levon, Vachaspati, Tanmay, Winitzki, Serge
P and CP violation in cosmology can be manifested as large-scale helical velocity flows in the ambient plasma and as primordial helical magnetic fields. We show that kinetic helicity at last...
Primordial magnetic fields and CP violation in the sky (2001)
It has been argued that electroweak baryogenesis generates a left-handed primordial magnetic field. The helicity density of the primordial magnetic field today is estimated to be $\sim 10^2 n_b$...
Space of kink solutions in SU(N)\times Z_2 (2001)
Pogosian, Levon, Vachaspati, Tanmay
We find $(N+1)/2$ distinct classes (``generations'') of kink solutions in an $SU(N)\times Z_2$ field theory. The classes are labeled by an integer $q$. The members of one class of kinks will be...
Zero modes of fermions with general mass matrix (2001)
Starkman, Glenn, Stojkovic, Dejan, Vachaspati, Tanmay
We analyze zero energy solutions of the Dirac equation in the background of a string-like configuration in an extension of the standard model which accommodates the most general fermionic mass matrix...
A class of kinks in SU(N)\times Z_2 (2001)
In a classical, quartic field theory with $SU(N) \times Z_2$ symmetry, a class of kink solutions can be found analytically for one special choice of parameters. We construct these solutions and...
Lectures on Cosmic Topological Defects (2001)
These lectures review certain topological defects and aspects of their cosmology. Unconventional material includes brief descriptions of electroweak defects, the structure of domain walls in...
Estimate of the primordial magnetic field helicity (2001)
Electroweak baryogenesis proceeds via changes in the non-Abelian Chern-Simons number. It is argued that these changes generate a primordial magnetic field with left-handed helicity. The helicity...
Neutrino Zero Modes on Electroweak Strings (2000)
Starkman, Glenn D., Stojkovic, Dejan, Vachaspati, Tanmay
Zero modes of massive standard model fermions have been found on electroweak Z-strings. A zero mode solution for a massless left-handed neutrino is also known, but was thought to be non-normalizable....
Pogosian, Levon, Vachaspati, Tanmay
We consider the Grand Unified SU(5) model with a small or vanishing cubic term in the adjoint scalar field in the potential. This gives the model an approximate or exact Z$_2$ symmetry whose breaking...
Spin and Dualization of SU(5) Dyons (2000)
Vachaspati, Tanmay, Steer, Daniele A.
Motivated by the dual standard model, we study the angular momentum spectrum of stable SU(5) dyons that can be transformed into purely electric states by a suitable duality rotation i.e. are...
Interaction of Magnetic Monopoles and Domain Walls (1999)
Pogosian, Levon, Vachaspati, Tanmay
We study the interaction of magnetic monopoles and domain walls in a model with SU(5)\times Z_2 symmetry by numerically evolving the field equations. We find that the monopoles unwind and dissipate...
What is the Homogeneity of our Universe Telling Us? (1999)
Trodden, Mark, Vachaspati, Tanmay
The universe we observe is homogeneous on super-horizon scales, leading to the ``cosmic homogeneity problem''. Inflation alleviates this problem but cannot solve it within the realm of conservative...
Semilocal and Electroweak Strings (1999)
Achucarro, Ana, Vachaspati, Tanmay
We review a class of non-topological defects in the standard electroweak model, and their implications. Starting with the semilocal string, which provides a counterexample to many well known...
Formation, Interaction and Observation of Topological Defects (1999)
In these lectures, I describe the formation of defect distributions in first-order phase transitions, then briefly discuss the relevance of defect interactions after a phase transition and the...
Cosmic microwave background anisotropy from wiggly strings (1999)
Pogosian, Levon, Vachaspati, Tanmay
We investigate the effect of wiggly cosmic strings on the cosmic microwave background radiation anisotropy and matter power spectrum by modifying the string network model used by Albrecht et al.. We...
It has been shown that sub-Planckian models of inflation require initial homogeneity on super-Hubble scales under certain commonly held assumptions. Here I remark on the possible implications of this...
Observation of Cosmic Acceleration and Determining the Fate of the Universe (1999)
Starkman, Glenn, Trodden, Mark, Vachaspati, Tanmay
Current observations of Type Ia supernovae provide evidence for cosmic acceleration out to a redshift of $z \lsim 1$, leading to the possibility that the universe is entering an inflationary epoch....
Causality and Cosmic Inflation (1998)
Vachaspati, Tanmay, Trodden, Mark
In the context of inflationary models with a pre-inflationary stage, in which the Einstein equations are obeyed, the weak energy condition is satisfied, and spacetime topology is trivial, we argue...
Creation and Structure of Baby Universes in Monopole Collisions (1998)
Borde, Arvind, Trodden, Mark, Vachaspati, Tanmay
Under certain circumstances, the collision of magnetic monopoles, topologically locked-in regions of false vacuum, leads to topological inflation and the creation of baby universes. The future...
On Random Bubble Lattices (1998)
De Laix, Andrew, Vachaspati, Tanmay
We study random bubble lattices which can be produced by processes such as first order phase transitions, and derive characteristics that are important for understanding the percolation of distinct...
Topological Defects in the Cosmos and Lab (1998)
Current theories of particle physics lead to the unavoidable conclusion that there must have been several phase transitions in the early universe. Further, in the context of these theories, it is...
Z_3 Strings and their Interactions (1998)
Heo, Junseong, Vachaspati, Tanmay
We construct Z_3 vortex solutions in a model in which SU(3) is spontaneously broken to Z_3. The model is truncated to one in which there are only two dimensionless free parameters and the interaction...
Topological Defects: Fossils from the Early Universe (1998)
In the context of current particle physics theories, it is quite likely that topological defects may be present in our universe. An observation of these fossils from the early universe would lead to...
Topological Inflation with Multiple Winding (1998)
De Laix, Andrew A., Trodden, Mark, Vachaspati, Tanmay
We analyze the core dynamics of critically coupled, superheavy gauge vortices in the (2+1) dimensional Einstein-Abelian-Higgs system. By numerically solving the Eistein and field equations for...
On a Dual Standard Model (1997)
I describe various aspects of the construction of a dual standard model including how it may be possible to obtain the charge spectrum, the family structure and spin of the known matter particles. I...
Formation of Topological Defects (1997)
In these lectures, I review cosmological phase transitions and the topological aspects of spontaneous symmetry breaking. I then discuss the formation of walls, strings and monopoles during phase...
Sweeping Away the Monopole Problem (1997)
Dvali, G., Liu, Hong, Vachaspati, Tanmay
We propose a new solution to the cosmological monopole problem in which domain walls sweep away the magnetic monopoles and subsequently decay. The solution does not require extensive fine tuning or...
It is shown that purely bosonic field theories can have configurations with half-integral angular momentum even when the topological magnetic charge of the configuration vanishes. This result is...
Relaxing the Geodesic Rule in Defect Formation Algorithms (1997)
Pogosian, Levon, Vachaspati, Tanmay
In studying the formation of topological defects, it is conventional to assume the ``geodesic rule'' which is equivalent to minimizing gradients of the order parameter. This assumption has been...
Gravitational Lensing Signature of Long Cosmic Strings (1997)
De Laix, Andrew A., Krauss, Lawrence M., Vachaspati, Tanmay
The gravitational lensing by long, wiggly cosmic strings is shown to produce a large number of lensed images of a background source. In addition to pairs of images on either side of the string, a...
Kernan, Peter J., Starkman, Glenn D., Vachaspati, Tanmay
Recently Cheng, Olinto, Schramm and Truran (COST) reexamined the constraints from big bang nucleosynthesis (BBN) on the strength of primordial magnetic fields. Their bottom line agreed with that of...
Family Replication in the Dual Standard Model (1996)
Liu, Hong, Starkman, Glenn D., Vachaspati, Tanmay
The family replication problem is addressed in the context of the dual standard model. The breaking of a simple grand unified group to $[G_{low} \times H_1 \times H_2 \times H_3]/Z_5^3$ and then...
Gravitational Lensing by Cosmic String Loops (1996)
De Laix, Andrew A, Vachaspati, Tanmay
We calculate the deflection of a light ray caused by the gravitational field of a cosmic string loop in the weak field limit and reduce the problem to a single quadrature over a time slice of the...
SU(5) Monopoles and the Dual Standard Model (1996)
We find the spectrum of magnetic monopoles produced in the symmetry breaking SU(5) to [SU(3)\times SU(2)\times U(1)']/Z_6 by constructing classical bound states of the fundamental monopoles. The...
Galactic Cosmic Strings as Sources of Primary Antiprotons (1996)
Starkman, Glenn D., Vachaspati, Tanmay
A possible signature of a class of superconducting cosmic strings trapped in the Milky Way plasma is the emission of low energy antiprotons due to baryon number violating processes on the string. We...
Perturbed Electroweak Strings and Fermion Zero Modes (1995)
The effect of perturbations of electroweak strings on quark zero modes is studied in 2+1 and 3+1 dimensions. As first discovered by Naculich, it is found that the bosonic perturbations that...
Aspects of ${}^3$He and the Standard Electroweak Model (1995)
Volovik, G. E., Vachaspati, Tanmay
We describe certain aspects of ${}^3He$ and compare them to related aspects of the standard electroweak model of particle physics. We note various similarities in the order parameter structure,...
An Attempt to Construct the Standard Model with Monopoles (1995)
We construct a model in which stable magnetic monopoles have magnetic charges that are identical to the electric charges on leptons and quarks and the colored monopoles are confined by strings in...
Topological Incarnations of Electroweak Defects (1995)
Kephart, Thomas W., Vachaspati, Tanmay
We propose a criterion to classify hybrid defects occurring in field theoretic models such as the standard electroweak model. This criterion leads us to consider the minimal extension of the...
Defect Production in Slow First Order Phase Transitions (1995)
Borrill, Julian, Kibble, T. W. B., Vachaspati, Tanmay, Vilenkin, Alexander
We study the formation of vortices in a U(1) gauge theory following a first-order transition proceeding by bubble nucleation, in particular the effect of a low velocity of expansion of the bubble...
Zero Modes on Linked Strings (1994)
Garriga, Jaume, Vachaspati, Tanmay
We study linked loops of string in the presence of bosonic condensates and fermionic zero modes on the strings. We find that the strings necessarily carry a current if the bosons have an...
Electroweak Strings, Zero Modes and Baryon Number (1994)
The Dirac equations for leptons and quarks in the background of an electroweak $Z-$string have zero mode solutions. If two loops of electroweak string are linked, the zero modes on one of the loops...
We consider dyon configurations in the standard electroweak model. In the presence of a $\theta$ term and no fermions, the usual result $q = (n+\theta /2\pi ) e$ is obtained for the electric charge...
Electroweak Strings, Sphalerons and Magnetic Fields (1994)
We describe electroweak strings and their ability to carry Chern-Simons number. Certain string configurations, for any $\theta_W$, carry Chern-Simons number equal to that of the sphaleron and we...
Topological Defects in Cosmology (1994)
The scenario of a cosmology with topological defects is surveyed starting from the field theoretic aspects and ending with a description of large-scale structure formation and magnetic field...
Electroweak String Configurations with Baryon Number (1994)
Vachaspati, Tanmay, Field, George B.
In the context of electroweak strings, the baryon number anomaly equation may be reinterpreted as a conservation law for baryon number minus helicity. Since the helicity is a sum of the link and...
Bound states can stabilize electroweak strings (1993)
Vachaspati, Tanmay, Watkins, Richard
We show that the stability of the electroweak Z-string is greatly improved by the presence of bound states of a complex scalar field. This stabilization mechanism could work for other embedded...
Production of Vortices by Scattering Particles (1993)
We give an action that can be used to describe the production of global vortices in 2+1 dimensions by scattering Nambu-Goldstone bosons. At strong self-coupling the action reduces to scalar QED with...
Barriola, Manuel, Vachaspati, Tanmay, Bucher, Martin
We give a prescription for embedding classical solutions and, in particular, topological defects in field theories which are invariant under symmetry groups that are not necessarily simple. After...
Do Global String Loops Collapse to Form Black Holes? (1993)
Fort, Joaquim, Vachaspati, Tanmay
Hawking has shown that the emission of gravitational radiation cannot prevent circular loops of gauged cosmic strings from collapsing into black holes. Here we consider the corresponding question for...
Detailed Stability Analysis of Electroweak Strings (1992)
James, Margaret, Perivolaropoulos, Leandros, Vachaspati, Tanmay
We give a detailed stability analysis of the Z-string in the standard electroweak model. We identify the mode that determines the stability of the string and numerically map the region of parameter...
Bound States Can Stabilize Electroweak Strings (1992)
Vachaspati, Tanmay, Watkins, Richard
We show that the electroweak $Z-$string can be stabilized by the presence of bound states of a complex scalar field. We argue that fermions coupled to the scalar field of the string can also make the...
Generalized Semilocal Theories and Higher Hopf Maps (1992)
Hindmarsh, Mark, Holman, Richard, Kephart, Thomas W., Vachaspati, Tanmay
\def\mon{S^3\stackrel{S^1}{\rightarrow}S^2} \def\inst{S^7\stackrel{S^3}{\rightarrow}S^4} \def\octo{S^{15}\stackrel{S^7}{\rightarrow}S^8} In semilocal theories, the vacuum manifold is fibered in a...