Results 1 - 10
of
25
String cosmology
"... Abstract: We derive the corrections to the Friedmann equation of order ρ 2 in the Randall-Sundrum (RS) model, where two 3-branes bound a slice of five-dimensional Anti-deSitter space. The effects of radion stabilization by the Goldberger-Wise mechanism are taken into account. Surprisingly, we find t ..."
Abstract
-
Cited by 48 (2 self)
- Add to MetaCart
(Show Context)
Abstract: We derive the corrections to the Friedmann equation of order ρ 2 in the Randall-Sundrum (RS) model, where two 3-branes bound a slice of five-dimensional Anti-deSitter space. The effects of radion stabilization by the Goldberger-Wise mechanism are taken into account. Surprisingly, we find that an inflaton on either brane will experience no order ρ 2 corrections in the Hubble rate H due to its own energy density, although an observer on the opposite brane does see such a correction. Thus there is no enhancement of the slow-roll condition unless inflation is simultaneously driven by inflatons on both branes. Similarly, during radiation domination, the ρ 2 correction to H on a given brane vanish unless there is nonvanishing energy density on the opposite brane. During the electroweak phase transition the correction can be large, but is has the wrong sign for causing sphalerons to go out of thermal equilibrium, so it cannot help electroweak baryogenesis. We discuss the differences
MCTP-08-62 Lüscher Term for k-string Potential from Holographic One Loop Corrections
, 809
"... We perform a systematic analysis of k-strings in the framework of the gauge/gravity correspondence. We discuss the Klebanov-Strassler supergravity background which is known to be dual to a confining supersymmetric gauge theory with chiral symmetry breaking. We obtain the k-string tension in agreemen ..."
Abstract
-
Cited by 6 (2 self)
- Add to MetaCart
(Show Context)
We perform a systematic analysis of k-strings in the framework of the gauge/gravity correspondence. We discuss the Klebanov-Strassler supergravity background which is known to be dual to a confining supersymmetric gauge theory with chiral symmetry breaking. We obtain the k-string tension in agreement with expectations of field theory. Our main new result is the study of one-loop corrections on the string theoretic side. We explicitly find the frequency spectrum for both the bosons and the fermions for quadratic fluctuations about the classical supergravity solution. Further we use the massless modes to compute 1/L contributions to the one loop corrections to the k-string energy. This corresponds to the Lüscher term contribution to the k-string potential on the gauge theoretic side of the correspondence.
MCTP-09-20 Tensions and Lüscher Terms for (2+1)-dimensional k-strings from Holographic Models
, 907
"... The leading term for the energy of a bound state of k-quarks and k-antiquarks is proportional to its separation L. These k-string configurations have a Lüscher term associated with their quantum fluctuations which is typically a 1/L correction to the energy. We review the status of tensions and Lüsc ..."
Abstract
-
Cited by 2 (0 self)
- Add to MetaCart
(Show Context)
The leading term for the energy of a bound state of k-quarks and k-antiquarks is proportional to its separation L. These k-string configurations have a Lüscher term associated with their quantum fluctuations which is typically a 1/L correction to the energy. We review the status of tensions and Lüscher terms in the context of lattice gauge theory, Hamiltonian methods, and gauge/gravity correspondence. Furthermore we explore how different representations of the k-string manifest themselves in the gauge/gravity duality. We calculate the Lüscher term for a strongly coupled SU(N) gauge theory in (2 + 1) dimensions using the gauge/gravity correspondence. Namely, we compute one-loop corrections to a probe D4-brane embedded in the Cvetič, Gibbons, Lü, and Pope supergravity background. We investigate quantum fluctuations of both the bosonic and the fermionic sectors.
2007 Energy radiation by cosmic superstrings in brane inflation. [e-Print: arXiv:arXiv:0710.4609
"... The dominant method of energy loss by a loop of cosmic D-strings in models of warped brane inflation is studied. It is shown that the energy loss via Ramond-Ramond field radiation can dominate by many orders of magnitude over the energy radiation via gravitational wave emission. The ratio of these t ..."
Abstract
-
Cited by 2 (0 self)
- Add to MetaCart
(Show Context)
The dominant method of energy loss by a loop of cosmic D-strings in models of warped brane inflation is studied. It is shown that the energy loss via Ramond-Ramond field radiation can dominate by many orders of magnitude over the energy radiation via gravitational wave emission. The ratio of these two energy loss mechanisms depends on the energy scale of inflation, the mass scale of string theory and whether it is a single-throat or a multi-throat inflationary scenario. This can have important consequences for the detection of cosmic superstrings in the near future. It is argued that the bounds from CMB anisotropies and BBN are the dominant cosmological sources to constrain the physical parameters of the network of cosmic superstrings, whereas the role of the gravitational wave-based experiments may be secondary.
CERN-PH-TH/2009-140 Zipping and Unzipping of Cosmic String Loops in Collision
, 907
"... In this paper the collision of two cosmic string loops is studied. After collision junctions are formed and the loops are entangled. We show that after their formation the junctions start to unzip and the loops disentangle. This analysis provides a theoretical understanding of the unzipping effect o ..."
Abstract
- Add to MetaCart
(Show Context)
In this paper the collision of two cosmic string loops is studied. After collision junctions are formed and the loops are entangled. We show that after their formation the junctions start to unzip and the loops disentangle. This analysis provides a theoretical understanding of the unzipping effect observed in numerical simulations of a network of cosmic strings with more than one type of cosmic strings. The unzipping phenomena have important effects in the evolution of cosmic string networks when junctions are formed upon collision, such as in a network of cosmic superstrings.
astro-ph/yymmnnn Cosmic String Detection via Microlensing of Stars
, 709
"... Abstract: Cosmic superstrings are produced towards the end of the brane inflation, a scenario realized in modern superstring theory. If the string tension is low enough, loops tend to be relatively long-lived. The resultant string network is expected to contain many loops which are smaller than typi ..."
Abstract
- Add to MetaCart
(Show Context)
Abstract: Cosmic superstrings are produced towards the end of the brane inflation, a scenario realized in modern superstring theory. If the string tension is low enough, loops tend to be relatively long-lived. The resultant string network is expected to contain many loops which are smaller than typical Galactic scales. Cosmic expansion damps the center of mass motion of the loops which then cluster like cold dark matter, eventually decaying by emission of gravitational radiation. Loops will lens stars within the galaxy and local group. We explore microlensing of stars as a tool to detect and to characterize some of the fundamental string and string network properties, including the dimensionless string tension Gµ/c 2 and the density of string loops within the Galaxy. As Gµ → 0 the intrinsic microlensing rate diverges as 1 / √ Gµ but experimental detection will be limited by shortness of the lensing timescale and/or smallness of the bending angle which each vary ∝ Gµ. We find that detection is feasible for a range of tensions. As an illustration, the planned optical astrometric survey mission, Gaia, should be able to detect numerous microlensing events for string networks with tensions 10 −12<
Relativistic Dynamics of
, 707
"... Moduli space dynamics of multi-D-vortices from D2 ¯ D2 (equivalently, parallel straight D-strings from D3 ¯ D3) is systematically studied. For the BPS D-vortices, we show through exact calculations that the classical motion of randomly-distributed n D-vortices is governed by a relativistic Lagrangia ..."
Abstract
- Add to MetaCart
(Show Context)
Moduli space dynamics of multi-D-vortices from D2 ¯ D2 (equivalently, parallel straight D-strings from D3 ¯ D3) is systematically studied. For the BPS D-vortices, we show through exact calculations that the classical motion of randomly-distributed n D-vortices is governed by a relativistic Lagrangian of free massive point-particles. When the head-on collision of two identical BPS D-vortices of zero radius is considered, it predicts either 90 ◦ scattering or 0 ◦ scattering equivalent to 180 ◦ scattering. Since the former leads to a reconnection of two identical D-strings and the latter does to a case of their passing through each other, two possibilities are consistent with the prediction of string theory. It is also shown that the force between two non-BPS vortices is repulsive. Although the obtained moduli space dynamics of multi-BPS-D-vortices is exact in classical regime, the quantum effect of an F-string pair production should be included in determining the probabilities of the reconnection and the passing through for fast-moving cosmic superstrings. 1 1
Five Easy Pieces: The Dynamics of Quarks in Strongly Coupled Plasmas
, 2009
"... We revisit the analysis of the drag a massive quark experiences and the wake it creates at a temperature T while moving through a plasma using a gravity dual that captures the renormalisation group runnings in the dual gauge theory. Our gravity dual has a black hole and seven branes embedded via Ouy ..."
Abstract
- Add to MetaCart
(Show Context)
We revisit the analysis of the drag a massive quark experiences and the wake it creates at a temperature T while moving through a plasma using a gravity dual that captures the renormalisation group runnings in the dual gauge theory. Our gravity dual has a black hole and seven branes embedded via Ouyang embedding, but the geometry is a deformation of the usual conifold metric. In particular the gravity dual has squashed two spheres, and a small resolution at the IR. Using this background we show that the drag of a massive quark receives corrections that are proportional to powers of log T when compared with the drag computed using AdS/QCD correspondence. The massive quarks map to fundamental strings in the dual gravity theory. We use the perturbation produced by these strings to compute the wake and compare with the results obtained using AdS/QCD correspondence. We also study the shear viscosity in the theory with running couplings, analyze the viscosity to entropy ratio and compare the result with the bound derived from AdS backgrounds. In the presence of higher order curvature square corrections from the back-reactions of the embedded D7 branes, we argue the possibility of the entropy to viscosity bound being violated. Finally, we show that our set-up could in-principle allow us to study a family of gauge theories at the boundary by cutting off the dual geometry respectively at various points in the radial direction. All these gauge theories can have well defined UV completions, and more interestingly, we demonstrate that any thermodynamical quantities derived from these theories would be completely independent of the cut-off scale and only depend on the temperature at which we define these theories. Such a result would justify the holographic renormalisabilities of these theories which we, in turn, also demonstrate. We give physical interpretations of these results and compare them with more realistic scenarios.
