14552385
Gödel black hole, closed timelike horizon and the study of particle emissions
We show that a particle, with positive orbital angular momentum, following an outgoing null/timelike geodesic, shall never reach the closed timelike horizon present in the (4 + 1)-dimensional rotating Gödel black hole space–time. Therefore a large part of this space–time remains inaccessible to a large class of geodesic observers, depending on the conserved quantities associated with them. We discuss how this fact and the existence of the closed timelike curves present in the asymptotic region make the quantum field theoretic study of the Hawking radiation, where the asymptotic observer states are a pre-requisite, unclear. However, the semi classical approach provides an alternative to verify the Smarr formula derived recently for the rotating Gödel black hole. We present a systematic analysis of particle emissions, specifically for scalars, charged Dirac spinors and vectors, from this black hole via the semiclassical complex path method.
12947810
Effect of a positive cosmological constant on cosmic strings
We study cosmic Nielsen-Olesen strings in space-times with a positive cosmological constant. For the free cosmic string in a cylindrically symmetric space-time, we calculate the contribution of the cosmological constant to the angle deficit, and to the bending of null geodesics. For a cosmic string in a Schwarzschild-de Sitter space-time, we use Kruskal patches around the inner and outer horizons to show that a thin string can pierce them.
118213552
Acoustic geometry through perturbation of mass accretion rate : I - radial flow in general static spacetime
We propose a novel perturbation scheme to perform the linear stability analysis of stationary transonic integral accretion solutions corresponding to the hydrodynamic non self-gravitating radial flow of matter in a general static black hole spacetime. We demonstrate that a metric independent perturbation scheme can be developed, which leads to the emergence of the relativistic acoustic geometry and ensures the stability of the background stationary solutions. The acoustic metric obtained by perturbing the mass accretion rate rate is found to be identical with that obtained through the perturbation of the velocity potential. Our work thus makes a crucial connection between two apparently disjoint fields of study - accretion astrophysics and analogue gravity phenomena. We also formally prove that acoustic horizons never form in the Rindler spacetime.
118446121
Mass function and particle creation in Schwarzschild–de Sitter spacetime
We construct a mass or energy function for the non-Nariai class Schwarzschild–de Sitter black hole spacetime in the region between the black hole and the cosmological event horizons. The mass function is local, positive definite, continuous and increases monotonically with the radial distance from the black hole event horizon. We derive the Smarr formula using this mass function, and demonstrate that the mass function reproduces the two-temperature Schwarzschild–de Sitter black hole thermodynamics, along with a term corresponding to the negative pressure due to positive cosmological constant. We further give a field theoretic derivation of the particle creation by both the horizons and discuss its connection with the mass function.
118589509
A note on Hawking radiation via complex path analysis
As long as we neglect backreaction, the Hawking temperature of a given black hole would not depend upon the parameters of the particle species we are considering. In the semiclassical complex path analysis approach of Hawking radiation, this has been verified by taking scalar and Dirac spinors separately for different stationary spacetime metrics. Here we show in a coordinate-independent way that for an arbitrary spacetime with any number of dimensions, the equations of motion for a Dirac spinor, a vector, spin-2 and spin- fields reduce to Klein–Gordon equations in the WKB semiclassical limit. We then obtain, under some suitable assumptions, the complex solutions of those resulting scalar equations across the Killing horizon of a stationary spacetime to get a coordinate-independent expression for the emission probability identical for all particle species. Finally we consider some explicit examples to demonstrate the validity of that expression.
118343992
No hair theorems for stationary axisymmetric black holes
AbstractWe present a non-perturbative proof of the no hair theorems corresponding to scalar and Procaﬁelds for stationary axisymmetric de Sitter black hole spacetimes. Our method also applies toasymptotically ﬂat and under a reasonable assumption, to asymptotically anti-de Sitter spacetimes.Keywords: Stationary black holes, no hair theorem, de Sitter 1 Introduction The classical no hair conjecture for black holes states that any gravitational collapse reaches a ﬁnalstationary state characterized only by a small number of parameters. A part of this conjecturehas been proven rigorously by taking diﬀerent matter ﬁelds, known as the no hair theorem (seee.g. [1, 2, 3]) and deals with the uniqueness of stationary black hole solutions characterized onlyby mass, angular momentum, and charges corresponding to long range gauge ﬁelds such as theelectromagnetic ﬁeld. Any non-trivial ﬁeld conﬁguration other than the long range gauge ﬁeldspresent at the exterior of a stationary black hole is known as ‘hair’. In particular, it has beenshown that static, spherically symmetric black holes do not support hair corresponding to scalarsin convex potentials, Proca-massive vector ﬁelds [4], or even gauge ﬁelds corresponding to theAbelian Higgs model [5, 6].All the above proofs assume the spacetime to be asymptotically ﬂat, i.e., one can reach spacelikeinﬁnity so that suﬃciently rapid fall-oﬀ conditions on the matter ﬁelds can be imposed there. Butrecent observations [7, 8] suggest that there is a strong possibility that our universe is endowedwith a small but positive cosmological constant Λ. It is generally expected that in that case thespacetime in its stationary state should have an outer or cosmological Killing horizon [9]. Thecosmological Killing horizon acts in general as a causal boundary (see e.g. [10]) so that no physicalobserver can communicate beyond this horizon along a future directed path. If there is a black
119226937
Supersymmetry Signals at the LHC under the most favorable SUGRA scenario
Given that it will take quite some time for the Large Hadron Collider (LHC) to reach its desired luminosity, it is important to investigate the most favorable scenario in which supersymmetry (SUSY) may be discovered at the early runs at the LHC. Our aim in this work is to find such a scenario within the gravity mediated SUSY breaking (SUGRA) framework and select a class of final states that warrant a discovery at the very early runs of the LHC. It turns out that such a situation can be associated with a scenario where gluinos are sufficiently light and so are the third generation scalars while the first two family scalars are heavy. We find that this can be achieved from a high-scale set-up with scalar mass non-universality in the third family and gaugino mass non-universality with $M_3 < M_1, M_2$. We show that the final state channels which are most favorable in such a region of parameter space are $4b+{E_{T}}\!\!\!\!/$, $4b+\ell+{E_{T}}\!\!\!\!/$ and $2b+2\ell+{E_{T}}\!\!\!\!/$. We also justify our claim by comparing the results with a minimal supergravity (mSUGRA) scenario with similar gluino mass.
12122294
Nonuniversal gaugino and scalar masses, hadronically quiet trileptons, and the Large Hadron Collider
We investigate the parameter space of the minimal supersymmetric standard model where the gluino and squark masses are much above 1 TeV but the remaining part of the sparticle spectrum is accessible to the Large Hadron Collider at CERN. After pointing out that such a scenario may constitute an important benchmark of gaugino/scalar nonuniversality, we find that hadronically quiet trileptons are rather useful signals for it. Regions of the parameter space, where the signal is likely to be appreciable, are identified through a detailed scan. The advantage of hadronically quiet trileptons over other types of signals is demonstrated.
119189999
Signatures of supersymmetry with non-universal Higgs mass at the Large Hadron Collider
A bstractWe discuss large non-universality in the Higgs sector at high scale in supersymmetric theories, in the context of the Large Hadron Collider (LHC). In particular, we note that if $$ {{m}_{{{{H}_u}}}}^2 - {{m}_{{{{H}_d}}}}^2 $$ is large and negative $$ ( \simeq {1}{{0}^{{6}}}{\text{Ge}}{{\text{V}}^{{2}}}) $$ at high scale, the lighter slepton mass eigenstates at the electroweak scale are mostly left chiral, in contrast to a minimal supergravity (mSUGRA) scenario. We utilise this feature to explore different chiral structures of the lowest-lying sleptons, using two methods. First, we study final states with same-sign ditaus. We find that an asymmetry parameter reflecting the polarisation of the taus provides a notable distinction. In addition, we study a charge asymmetry in the jet-lepton invariant mass distribution, arising from decay chains of left-chiral squarks leading to leptons of the first two families.
118339485
Two-component dark matter
A bstractWe study an extension of the Standard Model (SM) with two interacting cold Dark Matter (DM) candidates: a neutral Majorana fermion (ν) and a neutral scalar singlet (φ). The scalar φ interacts with the SM through the “Higgs portal” coupling while ν at the tree level interacts only with φ through Yukawa interactions. The relic abundance of ν and φ is found by solving the Boltzmann equations numerically; for the case mν > mφ we also derive a reliable approximate analytical solution. Effects of the interaction between the two DM components are discussed. A scan over the parameter space is performed to determine the regions consistent with the WMAP data for DM relic abundance, and with the XENON100 direct detection limits for the DM-nucleus cross section. We find that although a large region of the parameter space is allowed by the WMAP constraints, the XENON100 data severely restricts the parameter space. Taking into account only amplitudes generated at the tree level one finds three allowed regions for the scalar mass: mφ ~ 62.5 GeV (corresponding to the vicinity of the Higgs boson resonance responsible for φφ annihilation into SM particles), mφ ≃ 130 − 140 GeV and mφ ≳ 3 TeV. 1-loop induced ν-nucleon scattering has been also calculated and discussed. A possibility of DM direct detection by the CREST-II experiment was considered.
119096880
Constraints on Two-Component Dark Matter
We study 'Higgs Portal' 2-component Dark Matter scenario with two interacting cold Dark Matter (DM) candidates: a neutral scalar singlet ($\varphi$) and a neutral Majorana fermion ($\nu$). The relic abundance of $\varphi$ and $\nu$ is found assuming thermal DM production and solving the Boltzmann equations. We scan over the parameter space of the model to determine regions consistent with the WMAP data for DM relic abundance and the XENON100 direct detection limits for the DM-nucleus cross section.