@article{GuendelmanSingletonYongram2012,
  author    = {G{\"u}ndelman, Eduardo and Singleton, Douglas and Yongram, N.},
  title     = {A two measure model of dark energy and dark matter},
  series = {Journal of cosmology and astroparticle physics},
  journal   = {Journal of cosmology and astroparticle physics},
  number    = {11},
  publisher = {IOP Publ. Ltd.},
  address   = {Bristol},
  issn      = {1475-7516},
  doi       = {10.1088/1475-7516/2012/11/044},
  pages     = {12},
  year      = {2012},
  abstract  = {In this work we construct a unified model of dark energy and dark matter. This is done with the following three elements: a gravitating scalar field, phi with a non-conventional kinetic term, as in the string theory tachyon; an arbitrary potential, V (phi); two measures - a metric measure (root-g) and a non-metric measure (Phi). The model has two interesting features: (i) For potentials which are unstable and would give rise to tachyonic scalar field, this model can stabilize the scalar field. (ii) The form of the dark energy and dark matter that results from this model is fairly insensitive to the exact form of the scalar field potential.},
  language  = {en}
}
@article{ModakSingleton2012,
  author    = {Modak, Sujoy Kumar and Singleton, Douglas},
  title     = {Inflation with a graceful exit and entrance driven by Hawking radiation},
  series = {Physical review : D, Particles, fields, gravitation, and cosmology},
  volume    = {86},
  journal   = {Physical review : D, Particles, fields, gravitation, and cosmology},
  number    = {12},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {1550-7998},
  doi       = {10.1103/PhysRevD.86.123515},
  pages     = {9},
  year      = {2012},
  abstract  = {We present a model for cosmological inflation which has a natural "turn on'' and a natural "turn off'' mechanism. In our model inflation is driven by the Hawking-like radiation that occurs in Friedmann-Robertson-Walker (FRW) space-time. This Hawking-like radiation results in an effective negative pressure "fluid'' which leads to a rapid period of expansion in the very early Universe. As the Universe expands the FRW Hawking temperature decreases and the inflationary expansion turns off and makes a natural transition to the power-law expansion of a radiation dominated universe. The turn on mechanism is more speculative, but is based on the common hypothesis that in a quantum theory of gravity at very high temperatures/high densities Hawking radiation will stop. Applying this speculation to the very early Universe implies that the Hawking-like radiation of the FRW space-time will be turned off and therefore the inflation driven by this radiation will turn off.},
  language  = {en}
}
@article{KaeonikhomSingletonSushkovetal.2012,
  author    = {Kaeonikhom, Chakkrit and Singleton, Douglas and Sushkov, Sergey V. and Yongram, N.},
  title     = {Dynamics of Dirac-Born-Infeld dark energy interacting with dark matter},
  series = {Physical review : D, Particles, fields, gravitation, and cosmology},
  volume    = {86},
  journal   = {Physical review : D, Particles, fields, gravitation, and cosmology},
  number    = {12},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {1550-7998},
  doi       = {10.1103/PhysRevD.86.124049},
  pages     = {10},
  year      = {2012},
  abstract  = {We study the dynamics of Dirac-Born-Infeld (DBI) dark energy interacting with dark matter. The DBI dark energy model considered here has a scalar field with a nonstandard kinetic energy term, and has potential and brane tension that are power-law functions. The new feature considered here is an interaction between the DBI dark energy and dark matter through a phenomenological interaction between the DBI scalar field and the dark matter fluid. We analyze two different types of interactions between the DBI scalar field and the dark matter fluid. In particular we study the phase-space diagrams of and look for critical points of the phase space that are both stable and lead to accelerated, late-time expansion. In general we find that the interaction between the two dark components does not appear to give rise to late-time accelerated expansion. However, the interaction can make the critical points in the phase space of the system stable. Whether such stabilization occurs or not depends on the form of the interaction between the two dark components.},
  language  = {en}
}
@article{SchmidtSingleton2013,
  author    = {Schmidt, Hans-J{\"u}rgen and Singleton, Douglas},
  title     = {Exact radial solution in 2+1 gravity with a real scalar field},
  series = {Physics letters : B},
  volume    = {721},
  journal   = {Physics letters : B},
  number    = {4-5},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {0370-2693},
  doi       = {10.1016/j.physletb.2013.03.007},
  pages     = {294 -- 298},
  year      = {2013},
  abstract  = {In this Letter we give some general considerations about circularly symmetric, static space-times in 2 + 1 dimensions, focusing first on the surprising (at the time) existence of the BTZ black hole solution. We show that BTZ black holes and Schwarzschild black holes in 3 + 1 dimensions originate from different definitions of a black hole. There are two by-products of this general discussion: (i) we give a new and simple derivation of (2 + 1)-dimensional Anti-de Sitter (AdS) space-time; (ii) we present an exact solution to (2 + 1)-dimensional gravity coupled to a self-interacting real scalar field. The spatial part of the metric of this solution is flat but the temporal part behaves asymptotically like AdS space-time. The scalar field has logarithmic behavior as one would expect for a massless scalar field in flat space-time. The solution can be compared to gravitating scalar field solutions in 3 + 1 dimensions but with certain oddities connected with the (2 + 1)-dimensional character of the space-time. The solution is unique to 2 + 1 dimensions; it does not carry over to 3 + 1 dimensions.},
  language  = {en}
}
@article{SchmidtSingleton2013,
  author    = {Schmidt, Hans-J{\"u}rgen and Singleton, Douglas},
  title     = {Isotropic universe with almost scale-invariant fourth-order gravity},
  series = {Journal of mathematical physics},
  volume    = {54},
  journal   = {Journal of mathematical physics},
  number    = {6},
  publisher = {American Institute of Physics},
  address   = {Melville},
  issn      = {0022-2488},
  doi       = {10.1063/1.4808255},
  pages     = {14},
  year      = {2013},
  abstract  = {We study a class of isotropic cosmologies in the fourth-order gravity with Lagrangians of the form L = f(R) + k(G) where R and G are the Ricci and Gauss-Bonnet scalars, respectively. A general discussion is given on the conditions under which this gravitational Lagrangian is scale-invariant or almost scale-invariant. We then apply this general background to the specific case L = alpha R-2 + beta Gln G with constants alpha, beta. We find closed form cosmological solutions for this case. One interesting feature of this choice of f(R) and k(G) is that for very small negative value of the parameter beta, the Lagrangian L = R-2/3 + beta Gln G leads to the replacement of the exact de Sitter solution coming from L = R-2 (which is a local attractor) to an exact, power-law inflation solution a(t) = t(p) = t(-3/beta) which is also a local attractor. This shows how one can modify the dynamics from de Sitter to power-law inflation by the addition of a Gln G-term.},
  language  = {en}
}
@article{SchmidtSingleton2013,
  author    = {Schmidt, Hans-J{\"u}rgen and Singleton, Douglas},
  title     = {Exact radial solution in 2+1 gravity with a real scalar field},
  issn      = {0370-2693},
  year      = {2013},
  abstract  = {In this paper we give some general considerations about circularly symmetric, static space-times in 2+1 dimensions, focusing first on the surprising (at the time) existence of the BTZ black hole solution. We show that BTZ black holes and Schwarzschild black holes in 3+1 dimensions originate from different definitions of a black hole. There are two by-products of this general discussion: (i) we give a new and simple derivation of 2+1 dimensional Anti-de Sitter (AdS) space-time; (ii) we present an exact solution to 2+1 dimensional gravity coupled to a self-interacting real scalar field. The spatial part of the metric of this solution is flat but the temporal part behaves asymptotically like AdS space-time. The scalar field has logarithmic behavior as one would expect for a massless scalar field in flat space- time. The solution can be compared to gravitating scalar field solutions in 3+1 dimensions but with certain oddities connected with the 2+1 dimensional character of the space-time. The solution is unique to 2+1 dimensions; it does not carry over to 3+1 dimensions.},
  language  = {en}
}
@article{SchmidtSingleton2013,
  author    = {Schmidt, Hans-J{\"u}rgen and Singleton, Douglas},
  title     = {Isotropic universe with almost scale-invariant fourth-order gravity},
  year      = {2013},
  abstract  = {We study a broad class of isotropic vacuum cosmologies in fourth-order gravity under the condition that the gravitational Lagrangian be scale-invariant or almost scale-invariant. The gravitational Lagrangians considered will be of the form L = f(R) + k(G) where R and G are the Ricci and Gauss-Bonnet scalars respectively. Specifically we take f(R) = R^2n and k(G) = G^n or k(G) = G ln G. We find solutions in closed form for a spatially flat Friedmann space-time and interpret their asymptotic early-time and late-time behaviour as well as their inflationary stages. One unique example which we discuss is the case of a very small negative value of the parameter b in the Lagrangian L = R^2 + b G ln G which leads to the replacement of the exact de Sitter solution from L = R^2 (being a local attractor) to a power-law inflation exact solution also representing a local attractor. This shows how one can modify the dynamics from de Sitter to power-law inflation by the addition of the G ln G-term.},
  language  = {en}
}