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Yi Pang

Publications and source records attributed to Yi Pang.

At least 73 records · Page 4Linked to original sources
arXiv2014

Superfluid and Metamagnetic Phase Transitions in $ω$-deformed Gauged Supergravity

We study non-supersymmetric truncations of $ω$-deformed ${\cal N}=8$ gauged supergravity that retain a $U(1)$ gauge field and three scalars, of which two are neutral and one charged. We construct dyonic domain-wall and black hole solutions with AdS$_4$ boundary conditions when only one (neutral) scalar is non-vanishing, and examine their behavior as the magnetic field and temperature of the system are varied. In the infrared the domain-wall solutions approach either dyonic AdS$_2 \times \mathbb{R}^2$ or else Lifshitz-like, hyperscaling violating geometries. The scaling exponents of the latter are $z=3/2$ and $θ= -2$, and are independent of the $ω$-deformation. New $ω$-dependent AdS$_4$ vacua are also identified. We find a rich structure for the magnetization of the system, including a line of metamagnetic first-order phase transitions when the magnetic field lies in a particular range. Such transitions arise generically in the $ω$-deformed theories. Finally, we study the onset of a superfluid phase by allowing a fluctuation of the charged scalar field to condense, spontaneously breaking the abelian gauge symmetry. The mechanism by which the superconducting instability ceases to exist for strong magnetic fields is different depending on whether the field is positive or negative. Finally, such instabilities are expected to compete with spatially modulated phases.

hep-th↗
arXiv2014

$R^n$ Extension of Starobinsky Model in Old Minimal Supergravity

We provide a succinct way to construct the supersymmetric completion of $R^n$ $(n\ge3)$ in components using superconformal formulation of old minimal supergravity. As a consequence, we obtain the polynomial $f(R)$ supergravity extending the supersymmetric Starobinsky model to any higher power of $R$. The supersymmetric vacua in polynomial $f(R)$ supergravity are studied. We also present the $R^n$ extended Minimal Volkov-Akulov-Starobinsky Model.

hep-th↗
arXiv2013

Thermodynamics of Magnetised Kerr-Newman Black Holes

The thermodynamics of a magnetised Kerr-Newman black hole is studied to all orders in the appended magnetic field $B$. The asymptotic properties of the metric and other fields are dominated by the magnetic flux that extends to infinity along the axis, leading to subtleties in the calculation of conserved quantities such as the angular momentum and the mass. We present a detailed discussion of the implementation of a Wald-type procedure to calculate the angular momentum, showing how ambiguities that are absent in the usual asymptotically-flat case may be resolved by the requirement of gauge invariance. We also present a formalism from which we are able to obtain an expression for the mass of the magnetised black holes. The expressions for the mass and the angular momentum are shown to be compatible with the first law of thermodynamics and a Smarr type relation. Allowing the appended magnetic field $B$ to vary results in an extra term in the first law of the form $-μdB$ where $μ$ is interpreted as an induced magnetic moment. Minimising the total energy with respect to the total charge $Q$ at fixed values of the angular momentum and energy of the seed metric allows an investigation of Wald's process. The Meissner effect is shown to hold for electrically neutral extreme black holes. We also present a derivation of the angular momentum for black holes in the four-dimensional STU model, which is ${\cal N}=2$ supergravity coupled to three vector multiplets.

hep-th↗
arXiv2013

All Off-Shell R^2 Invariants in Five Dimensional N=2 Supergravity

We construct supersymmetric completions of various curvature squared terms in five dimensional supergravity with eight supercharges. Adopting the dilaton Weyl multiplet, we obtain the minimal off-shell supersymmetric Ricci scalar squared as well as all vector multiplets coupled curvature squared invariants. Since the minimal off-shell supersymmetric Riemann tensor squared and Gauss-Bonnet combination in the dilaton Weyl multiplet have been obtained before, both the minimal off-shell and the vector multiplets coupled curvature squared invariants in the dilation Weyl multiplet are complete. We also constructed an off-shell Ricci scalar squared invariant utilizing the standard Weyl multiplet. The supersymmetric Ricci scalar squared in the standard Weyl multiplet is coupled to n number of vector multiplets by construction, and it deforms the very special geometry. We found that in the supersymmetric AdS_5 vacuum, the very special geometry defined on the moduli space is modified in a simple way. Finally, we study the magnetic string and electric black hole solutions in the presence of supersymmetric Ricci scalar squared.

hep-th↗
arXiv2012

One-Loop Divergences in 6D Conformal Gravity

Using Exact Renormalization Group Equation approach and background field method, we investigate the one-loop problem in a six-dimensional conformal gravity theory whose Lagrangian takes the same form as holographic Weyl anomaly of multiple coincident M5-branes. We choose the backgrounds to be the symmetric Einstein spaces including S6, CP3, S2 \times S4, S2 \times CP2, S3 \times S3 and S2 \times S2 \times S2. Evaluating the functional sums gives power-law and logarithmic divergences. We extract from the specific values of logarithmic divergence on above backgrounds, the coefficient in front of Euler density and two linear equations constraining the coefficients in front of three type-B conformal invariants. As a test of the effectiveness of Exact Renormalization Group Equation approach to quantum conformal gravity, we reexaminethe one-loop problem in four-dimensional conformal gravity and confirm the logarithmic divergence derived from generalized Schwinger-DeWitt method.

hep-th↗
arXiv2012

Conformal Gravity and Extensions of Critical Gravity

Higher-order curvature corrections involving the conformally-invariant Weyl-squared action have played a role in two recent investigations of four-dimensional gravity; in critical gravity, where it is added to the standard cosmological Einstein-Hilbert action with a coefficient tuned to make the massive ghostlike spin-2 excitations massless, and in a pure Weyl-squared action considered by Maldacena, where the massive spin-2 modes are removed by the imposition of boundary conditions. We exhibit the connections between the two approaches, and we also generalise critical gravity to a wider class of Weyl-squared modifications to cosmological Einstein gravity where one can eliminate the massive ghostlike spin-2 modes by means of boundary conditions. The cosmological constant plays a crucial role in the discussion, since there is then a "window" of negative mass-squared spin-2 modes around AdS_4 that are not tachyonic. We also construct analogous conformal and non-conformal gravities in six dimensions.

hep-th↗
arXiv2012

Supersymmetric Solutions in Four-Dimensional Off-Shell Curvature-Squared Supergravity

Off-shell formulations of supergravities allow one to add closed-form higher-derivative super-invariants that are separately supersymmetric to the usual lower-derivative actions. In this paper we study four-dimensional off-shell N=1 supergravity where additional super-invariants associated with the square of the Weyl tensor and the square of the Ricci scalar are included. We obtain a variety of solutions where the metric describes domain walls, Lifshitz geometries, and also solutions of a kind known as gyratons. We find that in some cases the solutions can be supersymmetric for appropriate choices of the parameters. In some solutions the auxiliary fields may be imaginary. One may reinterpret these as real solutions in an analytically-continued theory. Since the supersymmetry transformation rules now require the gravitino to be complex, the analytically-continued theory has a "fake supersymmetry" rather than a genuine supersymmetry. Nevertheless, the concept of pseudo-supersymmetric solutions is a useful one, since the Killing spinor equations provide first-order equations for the bosonic fields.

hep-th↗
arXiv2011

Holographic de Sitter Universe

We propose to embed de Sitter space into five dimensional anti-de Sitter space to compute some physical quantities of interest, using the AdS/CFT correspondence. The static de Sitter can be considered as the conformal structure of the boundary of the hyperbolic AdS5 with a horizon, thus energy as well as entropy can be computed. The global dS can be embedded into a half-global AdS5, and the dS entropy can be regarded as entanglement entropy in this case. Finally, the inflationary dS can also be regarded as the boundary of AdS5, and this can be extended to include general cosmology with a positive cosmological constant, however at the price of introducing a naked null singularity in the bulk unless the cosmology is pure de Sitter space.

hep-th↗
arXiv2011

On Hybrid (Topologically) Massive Supergravity in Three Dimensions

A class of hybrid (topologically) massive off-shell supergravities coupled to an on-shell matter scalar multiplet was recently constructed. The auxiliary field in the off-shell multiplet is dynamical for generic values of the eight parameters. We find that by choosing the parameters appropriately, it remains non-dynamical. We perform linearized analysis around the supersymmetric AdS3 vacuum and its Minkowski limit. The ghost-free condition for the Minkowski vacuum is explored. For the AdS3 vacuum, we obtain the criticality condition and find that at the critical points, one of the two massive gravitons becomes pure gauge and decouples from the bulk physics, whilst the other has positive energy. We demonstrate that the mass of the BTZ black hole is non-negative at the critical points. We also investigate general BPS solutions. For certain parameter choices, we obtain exact solutions. In particular, we present the BPS string (domain-wall) solution that is dual to certain two-dimensional quantum field theory with an ultra-violet conformal fixed point.

hep-th↗
arXiv2011

Brief Note on AMD Conserved Quantities in Quadratic Curvature Theories

Motivated by the recent work on critical gravity theories in dimensions D>3, we reexamine the results in [arXiv:hep-th/0501044], where the conformal mass definition of Ashtekar, Magnon and Das (AMD) for asymptotically AdS space-times was generalized to incorporate curvature squared terms. The results in [arXiv:hep-th/0501044] appear to contradict the findings in critical gravity, where, using the methods of Deser and Tekin, black holes were shown to have zero mass. We show that after correcting an error in [arXiv:hep-th/0501044], the AMD approach actually produces results in complete agreement with those obtained by using the methods of Deser and Tekin.

hep-th↗
arXiv2010

Constructing Calabi-Yau Metrics From Hyperkahler Spaces

Recently, a metric construction for the Calabi-Yau 3-folds from a four-dimensional hyperkahler space by adding a complex line bundle was proposed. We extend the construction by adding a U(1) factor to the holomorphic (3,0)-form, and obtain the explicit formalism for a generic hyperkahler base. We find that a discrete choice arises: the U(1) factor can either depend solely on the fibre coordinates or vanish. In each case, the metric is determined by one differential equation for the modified Kahler potential. As explicit examples, we obtain the generalized resolutions (up to orbifold singularity) of the cone of the Einstein-Sasaki spaces Y^{p,q}. We also obtain a large class of new singular CY3 metrics with SU(2)\times U(1) or SU(2)\times U(1)^2 isometries.

hep-th↗
arXiv2010

A No-go Theorem Prohibiting Inflation in the Entropic Force Scenario

We show that to accommodate inflation in the entropic force scenario of Verlinde, it is necessary to introduce a negative temperature on a holographic screen, this will introduce several puzzles such as energy non-conservation. If one tries to modify the derivation of the Einstein equations to avoid a negative temperature, we prove that it is impossible to find a proper new definition of temperature to derive the Einstein equations.

hep-th↗
arXiv2010

Seven-Dimensional Gravity with Topological Terms

We construct new seven-dimensional gravity by adding two topological terms to the Einstein-Hilbert action. For certain choice of the coupling constants, these terms may be related to the R^4 correction to the 3-form field equation of eleven-dimensional supergravity. We derive the full set of the equations of motion. We find that the static spherically-symmetric black holes are unmodified by the topological terms. We obtain squashed AdS_7, and also squashed seven spheres and Q^{111} spaces in Euclidean signature.

hep-th↗
arXiv2010

More studies on Metamaterials Mimicking de Sitter space

We estimate the dominating frequencies contributing to the Casimir energy in a cavity of metamaterials mimicking de Sitter space, by solving the eigenvalue problem of Maxwell equations. It turns out the dominating frequencies are the inverse of the size of the cavity, and the degeneracy of these frequencies also explains our previous result on the unusually large Casimir energy. Our result suggests that carrying out the experiment in laboratory is possible theoretically.

physics.optics↗
arXiv2009

A Trouble with Hořava-Lifshitz Gravity

We study the structure of the phase space in Hořava-Lifshitz theory. With the constraints derived from the action, the phase space is described by five fields, thus there is a lack of canonical structure. The Poisson brackets of the Hamiltonian density do not form a closed structure, resulting in many new constraints. Taking these new constraints into account, it appears that there is no degree of freedom left, or the phase space is reduced to one with an odd number of fields.

hep-th↗
arXiv2009

Understanding light scalar meson by color-magnetic wavefunction in QCD sum rule

In this paper, we study the $0^{+}$ nonet mesons as tetraquark states with interpolating currents induced from the color-magnetic wavefunction. This wavefunction is the eigenfunction of effective color-magnetic Hamiltonian with the lowest eigenvalue, meaning that the state depicted by this wavefunction is the most stable one and is most probable to be observed in experiments. Our approach can be recognized as determining interpolating currents dynamically. We perform an OPE calculation up to dimension eight condensates and find that the best QCD sum rule is achived when the current induced from the color-magnetic wavefunction is a proper mixture of the tensor and pseudoscalar diquark-antidiquark bound states. Compared with previous results, to sigma(600) and kappa(800), our results appear better, due to larger pole contribution. The direct instanton contribution are also considered, which yields a consistent result with previous OPE results. Finally, we also discuss the eta' problem as a possible six-quark state.

hep-ph↗