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Radion tunneling in modified theories of gravity
https://repo.scoap3.org/record/25142
We consider a five dimensional warped spacetime where the bulk geometry is governed by higher curvature F ( R ) gravity. In this model, we determine the modulus potential originating from the scalar degree of freedom of higher curvature gravity. In the presence of this potential, we investigate the possibility of modulus (radion) tunneling leading to an instability in the brane configuration. Our results reveal that the parametric regions where the tunneling probability is highly suppressed, corresponds to the parametric values required to resolve the gauge hierarchy problem.Paul, TanmoyThu, 26 Apr 2018 13:09:19 GMThttps://repo.scoap3.org/record/25142urn:ISSN:1434-6052Springer/Società Italiana di Fisica2018-4-26Radion stabilization in higher curvature warped spacetime
https://repo.scoap3.org/record/23550
We consider a five dimensional AdS spacetime in presence of higher curvature term like F(R)=R+αR2 in the bulk. In this model, we examine the possibility of modulus stabilization from the scalar degrees of freedom of higher curvature gravity free of ghosts. Our result reveals that the model stabilizes itself and the mechanism of modulus stabilization can be argued from a geometric point of view. We determine the region of the parametric space for which the modulus (or radion) can to be stabilized. We also show how the mass and coupling parameters of radion field are modified due to higher curvature term leading to modifications of its phenomenological implications on the visible 3-brane.Das, AshmitaTue, 06 Feb 2018 12:29:43 GMThttps://repo.scoap3.org/record/23550urn:ISSN:1434-6052Springer/Società Italiana di Fisica2018-2-6Fermion localization in higher curvature and scalar–tensor theories of gravity
https://repo.scoap3.org/record/22642
It is well known that, in a braneworld model, the localization of fermions on a lower dimensional submanifold (say a TeV 3-brane) is governed by the gravity in the bulk, which also determines the corresponding phenomenology on the brane. Here we consider a five dimensional warped spacetime where the bulk geometry is governed by higher curvature like F ( R ) gravity. In such a scenario, we explore the role of higher curvature terms on the localization of bulk fermions which in turn determines the effective radion–fermion coupling on the brane. Our result reveals that, for appropriate choices of the higher curvature parameter, the profiles of the massless chiral modes of the fermions may get localized near the TeV brane, while those for massive Kaluza–Klein (KK) fermions localize towards the Planck brane. We also explore these features in the dual scalar–tensor model by appropriate transformations. The localization property turns out to be identical in the two models. This rules out the possibility of any signature of massive KK fermions in TeV scale collider experiments due to higher curvature gravity effects.Mitra, JoydipThu, 07 Dec 2017 04:04:02 GMThttps://repo.scoap3.org/record/22642urn:ISSN:1434-6052Springer/Società Italiana di Fisica2017-12-6Bouncing cosmology from warped extra dimensional scenario
https://repo.scoap3.org/record/22539
From the perspective of four dimensional effective theory on a two brane warped geometry model, we examine the possibility of “bouncing phenomena”on our visible brane. Our results reveal that the presence of a warped extra dimension lead to a non-singular bounce on the brane scale factor and hence can remove the “big-bang singularity”. We also examine the possible parametric regions for which this bouncing is possible.Das, AshmitaWed, 29 Nov 2017 19:09:01 GMThttps://repo.scoap3.org/record/22539urn:ISSN:1434-6052Springer/Società Italiana di Fisica2017-11-29Gravity stabilizes itself
https://repo.scoap3.org/record/21290
We show that a possible resolution to the stabilization of an extra spatial dimension (radion) can be obtained solely in the context of gravitational dynamics itself without the necessity of introducing any external stabilizing field. In this scenario the stabilized value of the radion field gets determined in terms of the parameters appearing in the higher curvature gravitational action. Furthermore, the mass of the radion field and its coupling to the standard model fields are found to be in the weak scale implying possible signatures in the TeV scale colliders. Some resulting implications are also discussed.Chakraborty, SumantaWed, 30 Aug 2017 01:08:02 GMThttps://repo.scoap3.org/record/21290urn:ISSN:1434-6052Springer/Società Italiana di Fisica2017-8-28Modulus stabilization in a non-flat warped braneworld scenario
https://repo.scoap3.org/record/19952
The stability of the modular field in a warped brane world scenario has been a subject of interest for a long time. Goldberger and Wise (GW) proposed a mechanism to achieve this by invoking a massive scalar field in the bulk space-time neglecting the back-reaction. In this work, we examine the possibility of stabilizing the modulus without bringing about any external scalar field. We show that instead of flat 3-branes as considered in Randall–Sundrum (RS) warped braneworld model, if one considers a more generalized version of warped geometry with de Sitter 3-brane, then the brane vacuum energy automatically leads to a modulus potential with a metastable minimum. Our result further reveals that in this scenario the gauge hierarchy problem can also be resolved for an appropriate choice of the brane’s cosmological constant.Banerjee, IndraniWed, 03 May 2017 16:40:27 GMThttps://repo.scoap3.org/record/19952urn:ISSN:1434-6052Springer/Società Italiana di Fisica2017-5-3Kinematics of radion field: a possible source of dark matter
https://repo.scoap3.org/record/18078
The discrepancy between observed virial and baryonic mass in galaxy clusters have lead to the missing mass problem. To resolve this, a new, non-baryonic matter field, known as dark matter, has been invoked. However, till date no possible constituents of the dark matter components are known. This has led to various models, by modifying gravity at large distances to explain the missing mass problem. The modification to gravity appears very naturally when effective field theory on a lower-dimensional manifold, embedded in a higher-dimensional spacetime is considered. It has been shown that in a scenario with two lower-dimensional manifolds separated by a finite distance is capable to address the missing mass problem, which in turn determines the kinematics of the brane separation. Consequences for galactic rotation curves are also described.Chakraborty, SumantaFri, 25 Nov 2016 16:41:19 GMThttps://repo.scoap3.org/record/18078urn:ISSN:1434-6052Springer/Società Italiana di Fisica2016-11-25Solving higher curvature gravity theories
https://repo.scoap3.org/record/17464
Solving field equations in the context of higher curvature gravity theories is a formidable task. However, in many situations, e.g., in the context of f ( R ) theories, the higher curvature gravity action can be written as an Einstein–Hilbert action plus a scalar field action. We show that not only the action but the field equations derived from the action are also equivalent, provided the spacetime is regular. We also demonstrate that such an equivalence continues to hold even when the gravitational field equations are projected on a lower-dimensional hypersurface. We have further addressed explicit examples in which the solutions for Einstein–Hilbert and a scalar field system lead to solutions of the equivalent higher curvature theory. The same, but on the lower-dimensional hypersurface, has been illustrated in the reverse order as well. We conclude with a brief discussion on this technique of solving higher curvature field equations.Chakraborty, SumantaThu, 13 Oct 2016 14:18:38 GMThttps://repo.scoap3.org/record/17464urn:ISSN:1434-6052Springer/Società Italiana di Fisica2016-10-8Lightest Kaluza–Klein graviton mode in a back-reacted Randall–Sundrum scenario
https://repo.scoap3.org/record/16597
In search of the extra dimensions in the ongoing LHC experiments, the signatures of the Randall–Sundrum (RS) lightest KK graviton have been in the main focus in recent years. The recent data from the dilepton decay channel at the LHC has determined the experimental lower bound on the mass of the RS lightest Kaluza–Klein (KK) graviton for different choices of the underlying parameters of the theory. In this work we explore the effects of the back-reaction of the bulk scalar field, which is employed to stabilise the RS model, in modifying the couplings of the lightest KK graviton with the standard model matter fields located on the visible brane. In such a modified background geometry we show that the coupling of the lightest KK graviton with the SM matter fields gets a significant suppression due to the inclusion of the back-reaction of the bulk stabilising scalar field. This implies that the back-reaction parameter weakens the signals from the RS scenario in collider experiments, which in turn explains the non-visibility of KK graviton in colliders. Thus we show that the modulus stabilisation plays a crucial role in the search of warped extra dimensions in collider experiments.Das, AshmitaThu, 28 Jul 2016 21:49:14 GMThttps://repo.scoap3.org/record/16597urn:ISSN:1434-6052Springer/Società Italiana di Fisica2016-7-28Penrose process in a charged axion–dilaton coupled black hole
https://repo.scoap3.org/record/15252
Using the Newman–Janis method to construct the axion–dilaton coupled charged rotating black holes, we show that the energy extraction from such black holes via the Penrose process takes place from the axion/Kalb–Ramond field energy responsible for rendering the angular momentum to the black hole. Determining the explicit form for the Kalb–Ramond field strength, which is argued to be equivalent to spacetime torsion, we demonstrate that at the end of the energy extraction process, the spacetime becomes torsion free with a spherically symmetric non-rotating black hole remnant. In this context, applications to physical phenomena, such as the emission of neutral particles in astrophysical jets, are also discussed. It is seen that the infalling matter gains energy from the rotation of the black hole, or equivalently from the axion field, and that it is ejected as a highly collimated astrophysical jet.Ganguly, ChandrimaMon, 18 Apr 2016 09:38:51 GMThttps://repo.scoap3.org/record/15252urn:ISSN:1434-6052Springer/Società Italiana di Fisica2016-4-18Effective gravitational field equations on m -brane embedded in n -dimensional bulk of Einstein and f(R) gravity
https://repo.scoap3.org/record/12722
We have derived effective gravitational field equations on a lower dimensional hypersurface (known as a brane), placed in a higher dimensional bulk spacetime for both Einstein and f(R) gravity theories. We have started our analysis on the n -dimensional bulk from which the effective field equations on a (n-1) -dimensional brane have been obtained by imposing Z2 symmetry. Subsequently, we have arrived at the effective equations in (n-2) dimensions starting from the effective equations for (n-1) -dimensional brane. This analysis has been carried out and is used to obtain the effective field equations for an (n-m) -dimensional brane, embedded in a n -dimensional bulk. Having obtained the effective field equations in Einstein gravity, we have subsequently generalized the effective field equation for an (n-m) -dimensional brane which is embedded in the n -dimensional bulk spacetime endowed with f(R) gravity. We have also presented applications of our results in the context of Einstein and f(R) gravity. In both cases we have discussed static spherically symmetric vacuum solutions as well as solutions in a cosmological context. Implications are also discussed.Chakraborty, SumantaWed, 18 Nov 2015 18:19:19 GMThttps://repo.scoap3.org/record/12722urn:ISSN:1434-6052Springer/Società Italiana di Fisica2015-11-18Can extra dimensional effects allow wormholes without exotic matter?
https://repo.scoap3.org/record/11863
We explore the existence of Lorentzian wormholes in the context of an effective on-brane, scalar-tensor theory of gravity. In such theories, the timelike convergence condition, which is always violated for wormholes, has contributions, via the field equations, from on-brane matter as well as from an effective geometric stress energy generated by a bulk-induced radion field. It is shown that, for a class of wormholes, the required on-brane matter, as seen by an on-brane observer in the Jordan frame, is not exotic and does not violate the Weak Energy Condition. The presence of the effective geometric stress energy in addition to on-brane matter is largely responsible for creating this intriguing possibility. Thus, if such wormholes are ever found to exist in the Universe, they would clearly provide pointers towards the existence of a warped extra dimension as proposed in the two-brane model of Randall and Sundrum.Kar, SayanThu, 17 Sep 2015 22:56:01 GMThttps://repo.scoap3.org/record/11863urn:ISSN:0370-2693Elsevier2017-03-23Cosmological evolution in a two-brane warped geometry model
https://repo.scoap3.org/record/10643
We study an effective 4-dimensional scalar–tensor field theory, originated from an underlying brane–bulk warped geometry, to explore the scenario of inflation. It is shown that the inflaton potential naturally emerges from the radion energy–momentum tensor which in turn results in an inflationary model of the Universe on the visible brane that is consistent with the recent results from the Planck's experiment. The dynamics of modulus stabilization from the inflaton rolling condition is demonstrated. The implications of our results in the context of recent BICEP2 results are also discussed.Kumar, SumitWed, 10 Jun 2015 13:56:26 GMThttps://repo.scoap3.org/record/10643urn:ISSN:0370-2693Elsevier2016-05-28Graviton modes in multiply warped geometry
https://repo.scoap3.org/record/10214
The negative results in the search for Kaluza–Klein graviton modes at the LHC, when confronted with the discovery of the Higgs, have been construed to have severely limited the efficacy of the Randall–Sundrum model as an explanation of the hierarchy problem. We show, though, that the presence of multiple warping offers a natural resolution of this conundrum through modifications in both the graviton spectrum and their couplings to the Standard Model fields.Arun, Mathew ThomasThu, 07 May 2015 14:58:04 GMThttps://repo.scoap3.org/record/10214urn:ISSN:0370-2693Elsevier2015-06-30Spherically symmetric brane spacetime with bulk f(R) gravity
https://repo.scoap3.org/record/8780
Introducing f(R) term in the five-dimensional bulk action we derive effective Einstein’s equation on the brane using Gauss–Codazzi equation. This effective equation is then solved for different conditions on dark radiation and dark pressure to obtain various spherically symmetric solutions. Some of these static spherically symmetric solutions correspond to black hole solutions, with parameters induced from the bulk. Specially, the dark pressure and dark radiation terms (electric part of Weyl curvature) affect the brane spherically symmetric solutions significantly. We have solved for one parameter group of conformal motions where the dark radiation and dark pressure terms are exactly obtained exploiting the corresponding Lie symmetry. Various thermodynamic features of these spherically symmetric space-times are studied, showing existence of second order phase transition. This phenomenon has its origin in the higher curvature term with f(R) gravity in the bulk.Chakraborty, SumantaTue, 13 Jan 2015 22:56:52 GMThttps://repo.scoap3.org/record/8780urn:ISSN:1434-6052Springer/Società Italiana di Fisica2015-1-14A step toward exploring the features of Gravidilaton sector in Randall–Sundrum scenario via lightest Kaluza–Klein graviton mass
https://repo.scoap3.org/record/4808
In this paper we study the role of the 5D Gauss–Bonnet corrections and two-loop higher genus contribution to the gravity action in type IIB string theory inspired low energy supergravity theory in the light of gravidilatonic interactions on the lightest Kaluza–Klein graviton mass spectrum. From the latest constraints on the lightest Kaluza–Klein graviton mass as obtained from the ATLAS dilepton search in 7 TeV proton–proton collision experiments, we have shown that due to the presence of Gauss–Bonnet and string loop corrections, the warping solution in an AdS5 bulk is quite distinct from the Randall–Sundrum scenario. We discuss the constraints on the model parameters to fit with the present ATLAS data.Choudhury, SayantanTue, 18 Nov 2014 11:04:43 GMThttps://repo.scoap3.org/record/4808urn:ISSN:1434-6052Springer/Società Italiana di Fisica2014-11-19Radion cosmology and stabilization
https://repo.scoap3.org/record/3979
We solve the Einstein equation in five-dimensional space-time for Randall–Sundrum Brane world model with time dependent radion field to study the variation of brane scale factor with time. We have shown that as the radion field decreases with time compactifying the extra dimension, the scale factor increases exponentially with time leading to an inflationary scenario. We have also proposed a time dependent generalization of the Goldberger–Wise moduli stabilization mechanism to explain the time evolution of the radion field to reach a stable value, after which the scale factor on the brane exits from inflationary expansion.Chakraborty, SumantaSun, 14 Sep 2014 06:55:53 GMThttps://repo.scoap3.org/record/3979urn:ISSN:1434-6052Springer/Società Italiana di Fisica2014-9-11Modulus stabilization in higher curvature dilaton gravity
https://repo.scoap3.org/record/3489
We propose a framework of modulus stabilization in two brane warped geometry scenario in presence of higher curvature gravity and dilaton in bulk space-time. In the prescribed setup we study various features of the stabilized potential for the modulus field, generated by a bulk scalar degrees of freedom with quartic interactions localized on the two 3-branes placed at the orbifold fixed points. We determine the parameter space for the gravidilaton and Gauss-Bonnet couplings required to stabilize the modulus in such higher curvature dilaton gravity setup.Sayantan ChoudhuryWed, 06 Aug 2014 04:18:58 GMThttps://repo.scoap3.org/record/3489urn:ISSN:1029-8479Springer/SISSA2014-08-01