Characteristic microwave-background distortions from collapsing spherical domain walls

Abstract

We analyze the magnitude and angular pattern of distortions of the microwave background by collapsing spherical domain walls. We find a characteristic pattern of redshift distortions of red or blue spikes surrounded by blue disks. The width and height of a spike is related to the diameter and magnitude of the disk. A measurement of the relations between these quantities thus can serve as an unambiguous indicator for a collapsing spherical domain wall. From the redshift distortion in the blue disks we find an upper bound on the surface energy density of the walls cr<8 MeV 3 .PACS numbers: 98.80.Cq, 98.70.Vc A phase transition in the early Universe that allows a scalar field to settle down in different vacuum expectation values in different regions of the Universe would produce domain walls 1 between these regions. The renewed interest in domain walls is due to a scenario of galaxy formation proposed by Hill, Schramm, and Fry 2 in which these topological defects form after recombination and provide the seeds for the clustering of baryons. An important criterion for the viability of such a model of structure formation is whether the induced distortion of the microwave background is compatible with the observed isotropy.In this paper we calculate the redshift distortion induced by collapsing spherical domain walls. 3 We find that they lead to a distinctive pattern in the angular temperature fluctuations of the microwave background. This paper was stimulated by a discussion with Watkins, who has studied the microwave distortions that result when photons pass through collapsing domain walls and found that a pattern of spots on the microwave sky arises. 4 A domain wall that comes within the cosmic horizon will collapse due to its surface tension. The collapse will proceed almost with the velocity of light until the radius of the bubble becomes comparable to the wall thickness and the wall decays into scalar bosons. 5 These bosons move outwards in a shell with a thickness comparable to that of the original wall. It is also possible that the bubble forms a black hole. Outside the collapsing bubble the gravitational field is equivalent to that of a point mass. Inside, however, because of the vanishing energy density, there is no gravitational field. A photon passing through the gravitational field of the bubble receives a shift in its energy (i.e., a redshift or blueshift) mainly due to three effects: 6 (i) a shift in energy equal to the difference in the gravitational potential at the points where the photon enters and leaves the bubble, (ii) a change in the potential caused by the cosmic expansion, and (iii) a time delay that photons traversing the gravitational potential suffer with respect to photons unaffected by the potential. In an expanding universe this last contribution always corresponds to a blueshift in the energy of the photon.The net change in the energy of the photon depends on the gravitational field along the path of the photon. There are three qualitatively different trajectories (see Fig. 1).(I) The pho...

Cosmic microwave background anisotropies generated by domain wall networks

“…Although some preliminary studies of the CMB signatures generated by domain walls have been done in the past [2,[12][13][14]), detailed studies of the anisotropies generated by these networks are yet to be performed. In this paper, we develop a numerical tool to compute the angular power spectrum generated by domain wall networks (in both the temperature and polarization channels), by adapting and extending the publicly available CMBACT code [15][16][17] in order to accommodate these networks.…”

Dasar-Dasar Optika Geometri

“…A phase transition in the early universe that allows a scalar field to settle down in different vacuum expectation values in different regions of the universe would produce domain walls between these regions [173].…”

“…Domain walls shrink due to its own tension [177]. A domain wall that comes within the cosmic horizon will collapse due to its surface tension [173]. The domain walls collapse under their own tension [172].…”

“…These bosons move outwards in a shell with a thickness comparable to that of the original domain wall. It is also possible that the bubble forms a black hole [173].…”

Statistical tests for the Gaussian nature of primordial fluctuations through CBR experiments

“…Various topological defects, notably soft domain wall bubbles [46], the global monopoles [47] or textures [24], are capable of producing spot-like CBR anisotropies of any size by appropriately choosing model parameters. However, before one relies on topological defects as an answer, one has to filter out the foreground contaminations carefully.…”