Fundamental Planck Scale Research Articles

Evaporating black holes: Constraints on anomalous emission mechanisms

Hawking radiation of astrophysical black holes is minute and thought to be unobservable. However, different mechanisms could contribute to an anomalously high emission rate: extra dimensions, new "dark" families of bosons or fermions, or a lower fundamental Planck scale. Do black holes flood the Universe with gravitational waves via mass loss? Here, we show that the formation of black hole binaries and the absence of a stochastic background of gravitational waves can limit the emission rate to $|\dot{M}|\lesssim 10^{-15}M_{\odot}/{\rm yr}$, seven orders of magnitude more stringent than bounds from resolvable inspiralling binaries.

Implications for the hierarchy problem, inflation and geodesic motion from fiber fabric of spacetime

In this paper, we represent a resolution for the hierarchy problem where the inverse size of the extra dimension and the fundamental Planck scale would all be of the order of the TeV scale by proposing a fiber fabric of spacetime. The origin of the large hierarchy is essentially due to the cosh function which is physically originated from the dynamics of the horizontal metric in the vacuum of non-zero energy. In addition, the fiber fabric of spacetime allows us to resolve elegantly and naturally the problems of the chirality fermions and stabilizing potential for the size of the extra dimension, which are usually encountered in the higher dimensional theories. Then, we explore the inflation with the modulus of the extra dimension identified as the inflaton where our slow-roll inflationary model belongs to the E-model class with n=1. We calculate the main inflationary observables which are consistent with the present experiments. Finally, we study how the geodesic motion of neutral test particles gets modified from the extension of spacetime. We compute the radius of the photon sphere, the innermost stable circular orbit, the perihelion shift, the light bending angle, and the observables of the strong gravitational lensing and the retrolensing phenomenon. By comparing the predicted values with the experimental observations, we determine the constraints on the fiber fabric of spacetime.

A New Black Hole Solution in Conformal Dilaton Gravity on a Warped Spacetime

An exact time-dependent solution of a black hole is found in a conformally invariant gravity model on a warped Randall-Sundrum spacetime, by writing the metric . Here, represents the “un-physical” spacetime and ω the dilaton field, which will be treated on equal footing as any renormalizable scalar field. In the case of a five-dimensional warped spacetime, we thereafter write . The dilaton field can be used to describe the different notion the in-going and outside observers have of the Hawking radiation by using different conformal gauge freedom. The disagreement about the interior of the black hole is explained by the antipodal map of points on the horizon. The free parameters of the solution can be chosen in such a way that is singular-free and topologically regular, even for ω → 0 . It is remarkable that the 5D and 4D effective field equations for the metric components and dilaton fields can be written in general dimension n = 4,5. From the exact energy-momentum tensor in Eddington-Finkelstein coordinates, we are able to determine the gravitational wave contribution in the process of evaporation of the black hole. It is conjectured that, in context of quantization procedures in the vicinity of the horizon, unitarity problems only occur in the bulk at large extra-dimension scale. The subtraction point in an effective theory will be in the UV only in the bulk, because the use of a large extra dimension results in a fundamental Planck scale comparable with the electroweak scale.

Signatures of microscopic black holes and extra dimensions at future neutrino telescopes

In scenarios with large extra dimensions (LEDs), the fundamental Planck scale can be low enough that collisions between high-energy particles may produce microscopic black holes. High-energy cosmic neutrinos can carry energies much larger than a PeV, opening the door to a higher energy range than Earth-based colliders. Here, for the first time, we identify a number of unique signatures of microscopic black holes as they would appear in the next generation of large-scale neutrino observatories such as IceCube-Gen2 and the Pacific Ocean Neutrino Explorer. These signatures include new event topologies, energy distributions, and unusual ratios of hadronic-to-electronic energy deposition, visible through Cherenkov light echos due to delayed neutron recombination. We find that the next generation of neutrino telescopes can probe LEDs with a Planck scale up to 6 TeV, though the identification of unique topologies could push their reach even further.

Gapped continuum Kaluza-Klein spectrum

We consider a warped five-dimensional model with an ultraviolet (UV) brane and, on top of the Standard Model isolated modes, continua of KK modes with different mass gaps for all particles: gauge bosons, fermions, graviton, radion and Higgs boson. The model can be considered as a modelization in five dimensions of gapped unparticles. The five dimensional metric has a singularity, at a finite (infinite) value of the proper (conformal) coordinate, which is admissible as it supports finite temperature in the form of a black hole horizon. An infrared (IR) brane, with particular jumping conditions, is introduced to trigger correct electroweak breaking. The gravitational metric is AdS5 near the UV brane, to solve the hierarchy problem with a fundamental Planck scale, and linear, in conformal coordinates, near the IR, as in the linear dilaton and five-dimensional clockwork models. The branes, and singularity, distances are fixed, à la Goldberger-Wise, by a bulk scalar field with brane potentials explicitly breaking the conformal symmetry. The bosonic continuum of KK modes with the smallest mass gap are those of gauge bosons, and so they are the most likely produced at the LHC. Mass gaps of the continuum of KK fermions do depend on their localization in the extra dimension. We have computed the spectral functions, and arbitrary Green’s functions, and shown how they can modify some Standard Model processes.

Search for new physics in final states with an energetic jet or a hadronically decaying W or Z boson and transverse momentum imbalance at s=13 TeV

A search for new physics using events containing an imbalance in transverse momentum and one or more energetic jets arising from initial-state radiation or the hadronic decay of W or Z bosons is presented. A data sample of proton-proton collisions at $\sqrt{s} = $ 13 TeV, collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 35.9 fb$^{-1}$, is used. The observed data are found to be in agreement with the expectation from standard model processes. The results are interpreted as limits on the dark matter production cross section in simplified models with vector, axial-vector, scalar, and pseudoscalar mediators. Interpretations in the context of fermion portal and nonthermal dark matter models are also provided. In addition, the results are interpreted in terms of invisible decays of the Higgs boson and set stringent limits on the fundamental Planck scale in the Arkani-Hamed, Dimopoulos, and Dvali model with large extra spatial dimensions.

Bounds on large extra dimensions from the Generalized Uncertainty Principle

The Generalized Uncertainty Principle (GUP) implies the existence of a physical minimum length scale [Formula: see text]. In this scenario, black holes must have a radius larger than [Formula: see text]. They are hotter and evaporate faster than in standard Hawking thermodynamics. We study the effects of the GUP on black hole production and decay at the LHC in models with large extra dimensions. Lower bounds on the fundamental Planck scale and the minimum black hole mass at formation are determined from black hole production cross-section limits by the CMS Collaboration. The existence of a minimum length generally decreases the lower bounds on the fundamental Planck scale obtained in the absence of a minimum length.

Bounds on large extra dimensions from the simulation of black hole events at the LHC

If large extra dimensions exist, the Planck scale may be as low as a TeV and microscopic black holes may be produced in high-energy particle collisions at this energy scale. We simulate microscopic black hole formation at the Large Hadron Collider and compare the simulation results with recent experimental data by the Compact Muon Solenoid collaboration. The absence of observed black hole events in the experimental data allows us to set lower bounds on the Planck scale and various parameters related to microscopic black hole formation for a number ($3-6$) of extra dimensions. Our analysis sets lower bounds on the fundamental Planck scale ranging from 0.6 TeV to 4.8 TeV for black holes fully decaying into Standard Model particles and 0.3 TeV to 2.8 TeV for black holes settling down to a remnant, depending on the minimum allowed black hole mass at formation. Formation of black holes with mass less than 5.2 TeV to 6.5 TeV (SM decay) and 2.2 TeV to 3.4 TeV (remnant) is excluded at 95\% C.L. Our analysis shows consistency with and difference from the CMS results.

Production of black holes and string balls in a two-dimensional split-fermion model

We present cross-sections for the black hole and string ball production in proton-proton collisions in a TeV-scale gravity model with split fermions in two dimensions. The cross-section for black hole and string ball production in the split-fermion model is smaller than in the non-split-fermion model. The drop of the cross-section for the string ball production can be one to two orders of magnitude with the increase of the width of the brane from $L=0$ to 15 $\text{TeV}^{-1}$. The cross-section for string ball production in two-dimensional split fermion model reduces more in comparison to black holes. Black holes are quite hard to be observed at the LHC. In fact, taking into account the current experimental limits on the fundamental Planck scale, black holes cannot be produced at the LHC. Cross-section for string ball production depends significantly on string coupling constant, making it very model dependent. We investigate the range of values of string coupling constant from 0.02 to 0.4. There has been no evidence for production of string balls at $\sqrt{s}=8$ TeV. A two-dimensional split fermion model with a extremely thick brane can account for the absence of signature of string balls for a world with the value of fundamental Planck scale even as low as 1 TeV.

Jet extinction from nonperturbative quantum gravity effects

The infrared-ultraviolet properties of quantum gravity suggest on very general grounds that hard short distance scattering processes are highly suppressed for center of mass scattering energies beyond the fundamental Planck scale. If this scale is not too far above the electroweak scale, these non-perturbative quantum gravity effects could be manifest as an extinction of high transverse momentum jets at the LHC. To model these effects we implement an Extinction Monte Carlo modification of the Pythia event generator based on a large damping Veneziano form factor modification of hard QCD scattering processes. Using this we illustrate the leading effects of extinction on the inclusive jet transverse momentum spectrum at the LHC. We estimate that an extinction mass scale of up to roughly half the center of mass beam collision energy could be probed with high statistics data.

Search for extra dimensions using diphoton events in 7 TeV proton–proton collisions with the ATLAS detector

Using data recorded in 2011 with the ATLAS detector at the Large Hadron Collider, a search for evidence of extra spatial dimensions has been performed through an analysis of the diphoton final state. The analysis uses data corresponding to an integrated luminosity of 2.12 fb−1 of s=7 TeV proton–proton collisions. The diphoton invariant mass (mγγ) spectrum is observed to be in good agreement with the expected Standard Model background. In the large extra dimension scenario of Arkani-Hamed, Dimopoulos and Dvali, the results provide 95% CL lower limits on the fundamental Planck scale between 2.27 and 3.53 TeV, depending on the number of extra dimensions and the theoretical formalism used. The results also set 95% CL lower limits on the lightest Randall–Sundrum graviton mass of between 0.79 and 1.85 TeV, for values of the dimensionless coupling k/M¯Pl varying from 0.01 to 0.1. Combining with previously published ATLAS results from the dielectron and dimuon final states, the 95% CL lower limit on the Randall–Sundrum graviton mass for k/M¯Pl=0.01 (0.1) is 0.80 (1.95) TeV.

Search for extra dimensions in the diphoton final state with ATLAS

The large difference between the Planck scale and the electroweak scale, known as the hierarchy problem, has been addressed in some models through the existence of extra spatial dimensions. A search for evidence of extra spatial dimensions has been performed, through an analysis of the diphoton final state in data recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. The analysis uses a dataset of 2.12 fb-1 of proton-proton collisions at sqrts=7 TeV. The diphoton invariant mass spectrum is observed to be in good agreement with the expected Standard Model (SM) background. We set 95 CL lower limits on the fundamental Planck scale in the context of the Arkani-Hamed, Dimopoulos, Dvali model (ADD) and on the lightest Kaluza Klein (KK) excitation mass in the context of the Randall-Sundrum model (RS).

Gauge-invariant quantum gravity corrections to Callan-Symanzik beta functions via the Vilkovisky-DeWitt method and gravity-assisted gauge unification

Gravity is the weakest force in nature, and the gravitational interactions with all standard model (SM) particles can be well described by perturbative expansions of the Einstein-Hilbert action as an effective theory, all the way up to energies below the fundamental Planck scale. We use Vilkovisky-DeWitt method to derive the first gauge-invariant nonzero gravitational power-law corrections to the running of gauge couplings, which make both Abel and non-Abel gauge interactions asymptotically free. We further demonstrate that the graviton-induced universal power-law runnings always assist the three SM gauge forces to reach unification around the Planck scale, irrespective of the detail of logarithmic corrections. We also compute the power-law corrections to the SM Higgs sector and derive modified triviality bound on the Higgs boson mass.

Non-relativistic limit of multidimensional gravity: exact solutions and applications

We found the exact solution of the Poisson equation for the multidimensional space with topology . This solution describes the smooth transition from the newtonian behavior 1/r3 for distances bigger than periods of tori (the extra dimension sizes) to multidimensional behavior 1/r1 + d3 + d in the opposite limit. In the case of one extra dimension d = 1, the gravitational potential is expressed via compact and elegant formulae. These exact solutions are applied to some practical problems to get the gravitational potentials for considered configurations. Found potentials are used to calculate the acceleration for point masses and gravitational self-energy. Models with test masses smeared over some (or all) extra dimensions are proposed. In ten-dimensional spacetime with three smeared extra dimensions, it is shown that the size of three rest extra dimensions can be enlarged up to a submillimeter for the case of 1 TeV fundamental Planck scale MPl(10). In the models where all extra dimensions are smeared, the gravitational potential exactly coincides with the newtonian one regardless of the size of the extra dimensions. Nevertheless, the hierarchy problem can be solved in these models.

Multidimensional gravity in the nonrelativistic limit

It is found the exact solution of the Poisson equation for the multidimensional space with topology $M_{3+d}=\mathbb{R}^3\times T^d$. This solution describes smooth transition from the newtonian behavior $1/r_3$ for distances bigger than periods of tori (the extra dimension sizes) to multidimensional behavior $1/r^{1+d}_{3+d}$ in opposite limit. In the case of one extra dimension $d=1$, the gravitational potential is expressed via compact and elegant formula. It is shown that the corrections to the gravitational constant in the Cavendish-type experiment can be within the measurement accuracy of Newton's gravitational constant $G_N$. It is proposed models where the test masses are smeared over some (or all) extra dimensions. In 10-dimensional spacetime with 3 smeared extra dimensions, it is shown that the size of 3 rest extra dimensions can be enlarged up to submillimeter for the case of 1TeV fundamental Planck scale $M_{Pl(10)}$. In the models where all extra dimensions are smeared, the gravitational potential exactly coincides with the newtonian one. Nevertheless, the hierarchy problem can be solved in these models.

SIGNATURES OF SINGLET NEUTRINOS IN LARGE EXTRA DIMENSIONS AT THE LHC

It is a challenge to explain why neutrinos are so light compared to other leptons. Small neutrino masses can be explained if right-handed fermions propagate in large extra dimensions. Fermions propagating in the bulk would have implications on Higgs boson decays. If the Higgs boson is discovered at the Large Hadron Collider (LHC), a detailed analysis may reveal the presence of large extra dimensions. This paper reviews the status of large extra-dimensional models in the context of the current limits on Higgs boson masses and the fundamental Planck scale in extra dimensions.

Higgs production and decay from TeV scale black holes at the LHC

We perform detailed study of the Higgs production and decay, when Higgs is emitted from the black holes produced in proton-proton collisions at the Large Hadron Collider. We show that black hole production can significantly enhance the signal for the Higgs search at the LHC. We evaluate rapidity distribution of diphotons and transverse momentum distribution of bottom quarks, photons, tau leptons, top quarks and W bosons from Higgs decay, when Higgs is emitted from the black hole and also in case when these particles are produced directly from the black hole evaporation. We compare our results with the standard model backgrounds. We find that Higgs production from black holes is dominant over standard model production for $p_T^H > 100$ GeV, when $M_P=1$TeV. Diphotons from Higgs, when Higgs is produced from evaporation of black holes, are dominant over the standard model prediction, for diphoton rapidity $|y_{\gamma \gamma}| \leq 1$, while bottom quarks are dominant over QCD background for large bottom quark transverse momentum, $p_T^b > 300$ GeV, when $M_P=1$ TeV. We show that measurements of the photon and bottom quark transverse momentum distribution can provide valuable information about the value of the fundamental Planck scale. We also propose a new signal for black hole production at the LHC, an onset of increasing transverse momentum distribution of bottom quarks with large transverse momentum.

Top quark production from black holes at the CERN LHC

LHC is expected to be a top quark factory. If the fundamental Planck scale is near a TeV, then we also expect the top quarks to be produced from black holes via Hawking radiation. In this Letter we calculate the cross sections for top quark production from black holes at the LHC and compare it with the direct top quark cross section via parton fusion processes at next-to-next-to-leading order (NNLO). We find that the top quark production from black holes can be larger or smaller than the pQCD predictions at NNLO depending upon the Planck mass and black hole mass. Hence the observation of very high rates for massive particle production (top quarks, Higgs or supersymmetry) at the LHC may be an useful signature for black hole production.

Bounds on large extra dimensions from the photon fusion process in SN1987A

The constraint on the Arkani-Hamed, Dimopoulos and Dvali model of extra dimensionscoming from photon annihilation into Kaluza–Klein gravitons in supernova cores isrevisited. In the two-photon process, for a conservative choice of the core parameters, weobtain the bound on the fundamental Planck scale TeV. The combined rate of energy loss due to nucleon–nucleon bremsstrahlung and photon annihilationprocesses is rederived, and it shows that the combined bounds add only a second decimal place toM*. The present study may strengthen the results that are available in thecurrent literature for the graviton emission from SN1987A, which puts verystrong constraints on models with large extra dimensions for the case ofn = 3.

Induced gravity on intersecting brane worlds: Maximally symmetric solutions

We explore models of intersecting brane worlds with induced gravity terms on codimension-one branes and on their intersection. Maximally symmetric solutions for the branes and the intersection are found. We find new self-accelerating solutions. In a 6D spacetime, the solutions realize the seesaw modification of gravity where the UV scale of the modification to 4D gravity is determined by 6D Planck scale given by ${M}_{6}\ensuremath{\sim}{10}^{\ensuremath{-}3}\text{ }\text{ }\mathrm{eV}$ and the IR scale of the modification is determined by ${M}_{6}^{2}/{M}_{4}\ensuremath{\sim}{H}_{0}\ensuremath{\sim}{10}^{\ensuremath{-}42}\text{ }\text{ }\mathrm{GeV}$, where ${H}_{0}$ is the present-day Hubble scale. We find that it is increasingly difficult to construct phenomenologically viable models in higher-dimensional spacetime due to the necessity to have the lower value for the fundamental Planck scale to realize the late time acceleration. It is found that the system also admits self-tuning solutions where the tension at the intersection does not change the geometry of the intersection. The induced gravity terms can avoid the necessity to compactify the extra dimensions. Finally, we discuss the possibility to have ordinary matter at the intersection, without introducing any regularization, using the induced gravity terms.