The fuzzy Dark Matter (FDM) is one of the recent models for dark matter. According to this model,... more The fuzzy Dark Matter (FDM) is one of the recent models for dark matter. According to this model, dark matter is made of very light scalar particles with considerable quantum mechanical effects on the galactic scales which solves many problems of the Cold Dark Matter (CDM). Here we use the observed data from the rotation curve of the Milky Way (MW) galaxy to compare the results from FDM and CDM models. We show that FDM adds a local peak on the rotation curve close to the center of the bulge where its position and amplitude depend on the mass of FDM particles. From fitting the observed rotation curve with our expectation from FDM, we find the mass of FDM to be m = 2.5 +3.6 −2.0 × 10 −21 eV. We note that the local peak of the rotation curve in MW can also be explained in the CDM model with an extra inner bulge model for the MW galaxy. We conclude that the FDM model explains this peak without need to extra structure for the bulge.
Aims. We present VRi photometric observations of the quadruply imaged quasar HE0435-1223, carried... more Aims. We present VRi photometric observations of the quadruply imaged quasar HE0435-1223, carried out with the Danish 1.54m telescope at the La Silla Observatory. Our aim was to monitor and study the magnitudes and colors of each lensed component as a function of time. Methods. We monitored the object during two seasons (2008 and 2009) in the VRi spectral bands, and reduced the data with two independent techniques: difference imaging and PSF (Point Spread Function) fitting. Results. Between these two seasons, our results show an evident decrease in flux by ≈ 0.2-0.4 magnitudes of the four lensed components in the three filters. We also found a significant increase (≈ 0.05-0.015) in their V − R and R − i color indices. Conclusions. These flux and color variations are very likely caused by intrinsic variations of the quasar between the observed epochs. Microlensing effects probably also affect the brightest "A" lensed component.
Light curves of four transit events of the transiting extrasolar planetary system WASP-4 are pres... more Light curves of four transit events of the transiting extrasolar planetary system WASP-4 are presented. The data were obtained using the Danish 1.5m telescope and DFOSC camera at ESO La Silla in 2008, with substantial telescope defocussing in order to improve the photometric precision of the observations. A Cousins R filter and exposure times of 120s were used. (1 data
Within the framework of an eternal inflationary scenario, a natural question regarding the produc... more Within the framework of an eternal inflationary scenario, a natural question regarding the production of eternal bubbles is the essential condition requires to have a universe capable of generating life. In either an open or a closed universe, we find an anthropic lower bound on the amount of e-folding in the order of 60 for the inflationary epoch, which results in the formation of large-scale structures in both linear and non-linear regimes. We extend the question of the initial condition of the universe to the sufficient condition in which we have enough initial dark matter and baryonic matter asymmetry in the early universe for the formation of galactic halos, stars, planets and consequently life. We show that the probability of a habitable universe is proportional to the asymmetry of dark matter and baryonic matter, while the cosmic budget of baryonic matter is limited by the astrophysical constrains.
Gravitational microlensing, ie the transient brightening of an observed star due to the bending o... more Gravitational microlensing, ie the transient brightening of an observed star due to the bending of light caused by the gravitational field of an intervening foreground star, was considered by Einstein as early as 1912 [1], but he concluded that" there is no great ...
Sohrab Rahvar Department of Physics, Sharif University of Technology, Tehran, PO Box 11365-9161, ... more Sohrab Rahvar Department of Physics, Sharif University of Technology, Tehran, PO Box 11365-9161, Iran Institute for Studies in Theoretical Physics and Mathematics, Tehran, POBox 19395-5531, Iran [email protected] ... Mohammad Sadegh Movahed Department of ...
We investigate the statistical anisotropy and Gaussianity of temperature fluctuations of Cosmic M... more We investigate the statistical anisotropy and Gaussianity of temperature fluctuations of Cosmic Microwave Background radiation (CMB) data from Wilkinson Microwave Anisotropy Probe survey, using the multifractal detrended fluctuation analysis, rescaled range and scaled windowed variance methods. The multifractal detrended fluctuation analysis shows that CMB fluctuations has a long range correlation function with a multifractal behavior. By comparing the shuffled and surrogate series of CMB data, we conclude that the multifractality nature of temperature fluctuation of CMB is mainly due to the long-range correlations and the map is consistent with a Gaussian distribution.
Page 1. arXiv:physics/9906039v1 [physics.plasm-ph] 22 Jun 1999 February 2, 2008 Water temperature... more Page 1. arXiv:physics/9906039v1 [physics.plasm-ph] 22 Jun 1999 February 2, 2008 Water temperature constraint on Sonoluminescence Sohrab Rahvar 1 Atomic Energy Organization of Iran, Bonab Research Center,POBox 113658486, Tehran,Iran ...
Proceedings of the International Astronomical …, Jan 1, 2004
The gravitational microlensing experiments in the direction of Large Magellanic Cloud (LMC) predi... more The gravitational microlensing experiments in the direction of Large Magellanic Cloud (LMC) predict a large amount of white dwarfs (∼ 20%) filling the galactic halo. However, the predicted white dwarfs have not been observed at the galactic halo. To interpret the microlensing results and resolving the mentioned problems, we use the hypothesis of spatially varying mass function of MACHOs, proposed by Kerins & Evans (1998) (hereafter KE). However the KE model is not compatible with the duration distribution of events (Rahvar 2004a). Here we use more realistic power-law model of MF, dn/dm ∝ m α for the MACHOs of halo. The index of MF in this model changes from −2.7 for stars with m > 1M at the central part of galactic halo to the substellar regime with an upper limit of −1 at the edge of halo. We show that in contrast to the abundant brown dwarfs of galactic halo, heavy MACHOs can be responsible for the microlensing events in the direction of LMC.
In recent years a large number of Hot Jupiters orbiting in a very close orbit around the parent s... more In recent years a large number of Hot Jupiters orbiting in a very close orbit around the parent stars have been explored with the transit and doppler effect methods. Here in this work we study the gravitational microlensing effect of a binary lens on a parent star with a Hot Jupiter revolving around it. Caustic crossing of the planet makes enhancements on the light curve of the parent star in which the signature of the planet can be detected by high precision photometric observations. We use the inverse ray shooting method with tree code algorithm to generate the combined light curve of the parent star and the planet. In order to investigate the probability of observing the planet signal, we do a Monte-Carlo simulation and obtain the observational optical depth of τ ∼ 10 −8 . We show that about ten years observations of Galactic Bulge with a network of telescopes will enable us detecting about ten Hot Jupiter with this method. Finally we show that the observation of the microlensing event in infra-red band will increase the probability for detection of the exo-planets.
Using astrometry of microlensing events we study the effect of angular momentum as compared to th... more Using astrometry of microlensing events we study the effect of angular momentum as compared to that of the parallax. For a rotating lens it is shown that the effect of the angular momentum deviates the center of images from that in the simple standard microlensing. This effect could be observed by future astrometry missions such as GAIA and SIM for lenses with angular momentum S ×10 48 kgm 2 sec −1 . It is shown that for extreme black hole lenses the corresponding mass should be more than 10 3 M ⊙ .
The fuzzy Dark Matter (FDM) is one of the recent models for dark matter. According to this model,... more The fuzzy Dark Matter (FDM) is one of the recent models for dark matter. According to this model, dark matter is made of very light scalar particles with considerable quantum mechanical effects on the galactic scales which solves many problems of the Cold Dark Matter (CDM). Here we use the observed data from the rotation curve of the Milky Way (MW) galaxy to compare the results from FDM and CDM models. We show that FDM adds a local peak on the rotation curve close to the center of the bulge where its position and amplitude depend on the mass of FDM particles. From fitting the observed rotation curve with our expectation from FDM, we find the mass of FDM to be m = 2.5 +3.6 −2.0 × 10 −21 eV. We note that the local peak of the rotation curve in MW can also be explained in the CDM model with an extra inner bulge model for the MW galaxy. We conclude that the FDM model explains this peak without need to extra structure for the bulge.
Aims. We present VRi photometric observations of the quadruply imaged quasar HE0435-1223, carried... more Aims. We present VRi photometric observations of the quadruply imaged quasar HE0435-1223, carried out with the Danish 1.54m telescope at the La Silla Observatory. Our aim was to monitor and study the magnitudes and colors of each lensed component as a function of time. Methods. We monitored the object during two seasons (2008 and 2009) in the VRi spectral bands, and reduced the data with two independent techniques: difference imaging and PSF (Point Spread Function) fitting. Results. Between these two seasons, our results show an evident decrease in flux by ≈ 0.2-0.4 magnitudes of the four lensed components in the three filters. We also found a significant increase (≈ 0.05-0.015) in their V − R and R − i color indices. Conclusions. These flux and color variations are very likely caused by intrinsic variations of the quasar between the observed epochs. Microlensing effects probably also affect the brightest "A" lensed component.
Light curves of four transit events of the transiting extrasolar planetary system WASP-4 are pres... more Light curves of four transit events of the transiting extrasolar planetary system WASP-4 are presented. The data were obtained using the Danish 1.5m telescope and DFOSC camera at ESO La Silla in 2008, with substantial telescope defocussing in order to improve the photometric precision of the observations. A Cousins R filter and exposure times of 120s were used. (1 data
Within the framework of an eternal inflationary scenario, a natural question regarding the produc... more Within the framework of an eternal inflationary scenario, a natural question regarding the production of eternal bubbles is the essential condition requires to have a universe capable of generating life. In either an open or a closed universe, we find an anthropic lower bound on the amount of e-folding in the order of 60 for the inflationary epoch, which results in the formation of large-scale structures in both linear and non-linear regimes. We extend the question of the initial condition of the universe to the sufficient condition in which we have enough initial dark matter and baryonic matter asymmetry in the early universe for the formation of galactic halos, stars, planets and consequently life. We show that the probability of a habitable universe is proportional to the asymmetry of dark matter and baryonic matter, while the cosmic budget of baryonic matter is limited by the astrophysical constrains.
Gravitational microlensing, ie the transient brightening of an observed star due to the bending o... more Gravitational microlensing, ie the transient brightening of an observed star due to the bending of light caused by the gravitational field of an intervening foreground star, was considered by Einstein as early as 1912 [1], but he concluded that" there is no great ...
Sohrab Rahvar Department of Physics, Sharif University of Technology, Tehran, PO Box 11365-9161, ... more Sohrab Rahvar Department of Physics, Sharif University of Technology, Tehran, PO Box 11365-9161, Iran Institute for Studies in Theoretical Physics and Mathematics, Tehran, POBox 19395-5531, Iran [email protected] ... Mohammad Sadegh Movahed Department of ...
We investigate the statistical anisotropy and Gaussianity of temperature fluctuations of Cosmic M... more We investigate the statistical anisotropy and Gaussianity of temperature fluctuations of Cosmic Microwave Background radiation (CMB) data from Wilkinson Microwave Anisotropy Probe survey, using the multifractal detrended fluctuation analysis, rescaled range and scaled windowed variance methods. The multifractal detrended fluctuation analysis shows that CMB fluctuations has a long range correlation function with a multifractal behavior. By comparing the shuffled and surrogate series of CMB data, we conclude that the multifractality nature of temperature fluctuation of CMB is mainly due to the long-range correlations and the map is consistent with a Gaussian distribution.
Page 1. arXiv:physics/9906039v1 [physics.plasm-ph] 22 Jun 1999 February 2, 2008 Water temperature... more Page 1. arXiv:physics/9906039v1 [physics.plasm-ph] 22 Jun 1999 February 2, 2008 Water temperature constraint on Sonoluminescence Sohrab Rahvar 1 Atomic Energy Organization of Iran, Bonab Research Center,POBox 113658486, Tehran,Iran ...
Proceedings of the International Astronomical …, Jan 1, 2004
The gravitational microlensing experiments in the direction of Large Magellanic Cloud (LMC) predi... more The gravitational microlensing experiments in the direction of Large Magellanic Cloud (LMC) predict a large amount of white dwarfs (∼ 20%) filling the galactic halo. However, the predicted white dwarfs have not been observed at the galactic halo. To interpret the microlensing results and resolving the mentioned problems, we use the hypothesis of spatially varying mass function of MACHOs, proposed by Kerins & Evans (1998) (hereafter KE). However the KE model is not compatible with the duration distribution of events (Rahvar 2004a). Here we use more realistic power-law model of MF, dn/dm ∝ m α for the MACHOs of halo. The index of MF in this model changes from −2.7 for stars with m > 1M at the central part of galactic halo to the substellar regime with an upper limit of −1 at the edge of halo. We show that in contrast to the abundant brown dwarfs of galactic halo, heavy MACHOs can be responsible for the microlensing events in the direction of LMC.
In recent years a large number of Hot Jupiters orbiting in a very close orbit around the parent s... more In recent years a large number of Hot Jupiters orbiting in a very close orbit around the parent stars have been explored with the transit and doppler effect methods. Here in this work we study the gravitational microlensing effect of a binary lens on a parent star with a Hot Jupiter revolving around it. Caustic crossing of the planet makes enhancements on the light curve of the parent star in which the signature of the planet can be detected by high precision photometric observations. We use the inverse ray shooting method with tree code algorithm to generate the combined light curve of the parent star and the planet. In order to investigate the probability of observing the planet signal, we do a Monte-Carlo simulation and obtain the observational optical depth of τ ∼ 10 −8 . We show that about ten years observations of Galactic Bulge with a network of telescopes will enable us detecting about ten Hot Jupiter with this method. Finally we show that the observation of the microlensing event in infra-red band will increase the probability for detection of the exo-planets.
Using astrometry of microlensing events we study the effect of angular momentum as compared to th... more Using astrometry of microlensing events we study the effect of angular momentum as compared to that of the parallax. For a rotating lens it is shown that the effect of the angular momentum deviates the center of images from that in the simple standard microlensing. This effect could be observed by future astrometry missions such as GAIA and SIM for lenses with angular momentum S ×10 48 kgm 2 sec −1 . It is shown that for extreme black hole lenses the corresponding mass should be more than 10 3 M ⊙ .
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