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H. Arfaei

Publications and source records attributed to H. Arfaei.

At least 19 recordsLinked to original sources
arXiv2021

A template-free approach for waveform extraction of gravitational wave events

We develop a general data-driven and template-free method for the extraction of event waveforms in the presence of background noise. Recent gravitational-wave observations provide one of the significant scientific areas requiring data analysis and waveform extraction capability. We use our method to find the waveforms for the reported events from the first, second, and third LIGO observation runs (O1, O2, and O3). Using the instantaneous frequencies derived by the Hilbert transform of the extracted waveforms, we provide the physical time delays between the arrivals of gravitational waves to the detectors.

astro-ph.IM↗
arXiv2014

Gauge Invariant Cutoff QED

A hidden generalized gauge symmetry of a cutoff QED is used to show the renormalizability of QED. In particular, it is shown that corresponding Ward identities are valid all along the renormalization group flow. The exact Renormalization Group flow equation corresponding to the effective action of a cutoff lambda phi^4 theory is also derived. Generalization to any gauge group is indicated.

hep-th↗
arXiv2008

Double Horizon Limit, AdS Geometry and Entropy Function

We start from a generic metric which describes four dimensional stationary black holes in an arbitrary theory of gravity and show that the AdS_2 part of the near horizon geometry is a consequence of the double-horizon limit and finiteness . We also show that the field configurations of the near horizon are determined if the same conditions are applied to the equations of motion. This is done by showing that in the double-horizon limit field equations at the horizon decouple from the bulk of the space. Solving these equations gives the near horizon field configurations. It is shown that these decoupled equations can be obtained from an action derived from the original action by applying the double-horizon condition. Our results agree with the entropy function method.

hep-th↗
arXiv2007

Double-Horizon Limit and Decoupling of the Dynamics at the Horizon

We show that the attractor mechanism for generic black hole is a consequence of the double-horizon. Investigation of equations of motion shows that in the case of the double-horizon black holes, the dynamics of the geometry, the scalars and the gauge fields at the horizon decouples from the rest of the space. In the general case, the value of the fields at the horizon satisfies a number of differential equations of functions of the $θ$ coordinate. We show this for the case of rotating and non-rotating electrically charged black holes in the general two derivative theories of gravity and f(R) gravities including the theories with cosmological constant.

hep-th↗
arXiv2006

On the Anomalies and Schwinger Terms in Noncommutative Gauge Theories

Invariant (nonplanar) anomaly of noncommutative QED is reexamined. It is found that just as in ordinary gauge theory UV regularization is needed to discover anomalies, in noncommutative case, in addition, an IR regularization is also required to exhibit existence of invariant anomaly. Thus resolving the controversy in the value of invariant anomaly, an expression for the unintergrated anomaly is found. Schwinger terms of the current algebra of the theory are derived.

hep-th↗
arXiv2002

Gravity on Noncommutative D-Branes

The effective action for the low energy scattering of two gravitons with a D-brane in the presence of a constant antisytmetric $B$ field in bosonic string theory is calculated and the modification to the standard D-brane action to first order in $α'$ is obtained.

hep-th↗
arXiv2000

Phenomenological Consequences of Non-commutative QED

In the context of the noncommutative QED we consider few phenomena which reflect the noncommutativity. In all of them the new interactions in the Feynmann diagrams that are responsible for the deviation from the standard QED results. These deviations appear as the violations of Lorentz symmetry. We suggest experimental situations where these effects may be observed. The extra phases have far reaching consequences including violation of crossing symmetry. Considering the e-p scattering and Compton scattering the electric dipole moments of the electron and the photon is calculated.

hep-th↗
arXiv1999

Mixed Branes Interaction in Compact Spacetime

We present a general description of two mixed branes interactions. For this we consider two mixed branes with dimensions p_1 and p_2, in external field B_{μν} and arbitrary gauge fields A^1_{α_1} and A^2_{α_2} on the world volume of them, in spacetime in which some of its directions are compactified on circles with different radii. Some examples are considered to clear these general interactions. Finally contribution of the massless states on the interactions is extracted. Closed string with mixed boundary conditions and boundary state formalism, provide useful tools for calculation of these interactions.

hep-th↗
arXiv1999

Branes with Background Fields in Boundary State Formalism

Interaction of branes in presence of internal gauge fields is considered by using the boundary state formalism. This approach enables us to consider the problems that are not easily accessible to the canonical approach via open strings. The effects of compactification of some of the dimensions on tori are also discussed. Also we study the massless state contribution on this interaction.

hep-th↗
arXiv1999

Noncommutative Geometry From Strings and Branes

Noncommutative torus compactification of Matrix model is shown to be a direct consequence of quantization of the open strings attached to a D-membrane with a non-vanishing background $B$ field. We calculate the BPS spectrum of such a brane system using both string theory results and DBI action. The DBI action leads to a new transformation property of the compactification radii under the $SL(2,Z)_N$ transformations.

hep-th↗
arXiv1998

Mixed Branes and M(atrix) Theory on Noncommutative Torus

We derive the noncommutative torus compactification of M(atrix) theory directly from the string theory by imposing mixed boundary conditions on the membranes. The relation of various dualities in string theory and M(atrix) theory compactification on the noncommutative torus are studied.

hep-th↗
arXiv1998

Distributed Systems of Intersecting Branes at Arbitrary Angles

A `reduced' action formulation for a general class of the supergravity solutions, corresponding to the `marginally' bound `distributed' systems of various types of branes at arbitrary angles, is developed. It turns out that all the information regarding the classical features of such solutions is encoded in a first order Lagrangian (the `reduced' Lagrangian) corresponding to the desired geometry of branes. The marginal solution for a system of $N$ such distributions (for various distribution functions) span an $N$ dimensional submanifold of the fields' configuration (target) space, parametrised by a set of $N$ independent harmonic functions on the transverse space. This submanifold, which we call it as the `$H$-surface', is a null surface with respect to a metric on the configuration space, which is defined by the reduced Lagrangian. The equations of motion then transform to a set of equations describing the embedding of a null geodesic surface in this space, which is identified as the $H$-surface. Using these facts, we present a very simple derivation of the conventional orthogonal solutions together with their intersection rules. Then a new solution for a (distributed) pair of $p$-branes at SU(2) angles in $D$ dimensions is derived.

hep-th↗
arXiv1998

Mixed Boundary Conditions and Brane-String Bound States

In this article we consider open strings with mixed boundary conditions (a combination of Neumann and Dirichlet conditions at each end). We discuss how their end points show a $D_p$-brane with NS-NS charge, i.e. a bound state of a D-brane with a fundamental strings. We show that these branes are BPS saturated. In the case of one-branes, we show that their mass densities are in agreement with IIb SUGRA which is Sl(2,Z) invariant. Using Chan-Paton factors, we extend our results to the case of bound states of $n$ D-strings and $m$ F-strings. These string theoretic results are also checked in the effective field theory limit.

hep-th↗
arXiv1997

D-brane Thickness

The scale in the D-brane theory is discussed from different points of view. It is shown that scattering of a $D_4$-brane by a $D_0$-brane gives the condition to penetrate beyond the string scale.

hep-th↗
arXiv1997

D-brane Interactions, World-sheet Parity and Anti-Symmetric Tensor

Using world-sheet parity we show that mixed D and N components of D-strings are dual to the anti-symmetric $B_{μν}$ field. The contribution of the latter is responsible for the reduction and even removal of all the interactions between two dissimilar D-branes.

hep-th↗
arXiv1996

Different D-brane Interactions

We use rotation of one D-brane with respect to the other to reveal the hidden structure of D-branes in type-II theories. This is done by calculation of the interaction amplitude for two different parallel and angled branes. The analysis of strings with different boundary conditions at the ends is also given. The stable configuration for two similar branes occurs when they are anti-parallel. For branes of different dimensions stability is attained for either parallel or anti-parallel configurations and when dimensions differ by four the amplitude vanishes at the stable point. The results serve as more evidence that D-branes are stringy descriptions of non-perturbative extended solutions of SUGRA theories, as low energy approximation of superstrings.

hep-th↗
arXiv1996

WZNW Models from Non-Standard Bilinear Forms

We study the WZNW models based on nonstandard bilinear forms. We approach the problem from algebraic, perturbative and functional exact methods. It is shown that even in the case of integer $k$ we can find irrational CFT's. We prove that when the base group is noncompact with nonabelian maximal compact subgroup, the Kac-Moody representations are nonunitary.

hep-th↗