Some Implications of Two Forms of the Generalized Uncertainty Principle

Various theories of quantum gravity predict the existence of a minimum length scale, which leads to the modification of the standard uncertainty principle to the Generalized Uncertainty Principle (GUP). In this paper, we study two forms of the GUP and calculate their implications on the energy of the harmonic oscillator and the Hydrogen atom more accurately than previous studies. In addition, we show how the GUP modifies the Lorentz force law and the time-energy uncertainty principle.


Introduction
Developing a theory of quantum gravity is currently one of the main challenges in theoretical physics. Various approaches predict the existence of a minimum length scale [1,2] that leads to the modification of the Heisenberg Uncertainty Principle: to the Generalized Uncertainty Principle (GUP) [3,4]: In this article, we study two forms of the GUP. The first (GUP1) [5,6] is: which follows from the modified commutation relation [6]: The second (GUP2) [7,8] is: which follows from the proposed modified commutation relation [7]:  is a constant usually assumed to be of order unity. In addition to a minimum measurable length, GUP2 implies a maximum measurable momentum. The commutation relation (4) admits the following representation in position space [9,10]: where 0 0 , i i x p satisfy the canonical commutation relation 0 0 . ,

This definition modifies any
Hamiltonian near the Planck scale to [9,10]: Similarly, (6) admits the definition [7,8]:  e-mail: moh.m.khalil@gmail.com Therefore, the relative change in energy is: The first term in (13) differs from that derived in [12] by a factor of three, because instead of the commutation relation (4) they use the relation     2 1 , GUP1-second order: The second order correction can be calculated using second order perturbation theory [13, P.256 Applying the raising and lowering operators: Because of the delta functions and the orthogonality of the Eigenfunctions, squaring the above expression means squaring each term individually. After simplifying and dividing by n E : which agrees with the expression derived in [8] when 0 n  . GUP2-second order: The second order correction for the 3 0 p term can be calculated using the same method that led to (18): Simplifying and dividing by n E : which agrees with the expression derived in [8] when 1/ 2 32 Adding (14) and (18) Adding (19), (23) and (24) It is interesting to note that to , the effect of GUP2 is to add a constant shift to all energy levels.
To compare (25) and (26) with experiment, consider an ion in a Penning trap; its motion is effectively a one-dimensional harmonic oscillator [14]. The accuracy of mass determination increases linearly with charge, so let us suppose it is possible to use completely ionized lead atoms, which have an atomic number of 82. Suppose that the magnetic field in the Penning trap is       (25) and (26), as a function of n . It is clear that the difference between the corrections of GUP1 and GUP2 increases with increasing n . That difference might prove useful in future experiments to differentiate between the two GUPs.
The best accuracy for mass determination for stable ions in a penning trap is [14]  . These bounds can be lowered in future experiments by using: Penning traps with higher mass determination accuracy, ions with higher charge, and stronger magnetic fields.

Hydrogen atom
The effect of GUP1 on the spectrum of the hydrogen atom was calculated to first order in [15] by doing the integral to find the expectation value of the perturbed Hamiltonian. In this section, we use a simpler method, adopted from [13, P.269], to get the same result. After that, we calculate the effect of GUP2 on the spectrum of hydrogen, which, to my knowledge, was not done before.
The GUP1-corrected Hamiltonian for Hydrogen takes the form: where 2 0 / 4 k e    , the change in energy to first order can be found as follows: where we used the hermiticity of 2 which agrees with the expression derived in [15], and is maximum when 5 The GUP2-corrected Hamiltonian for Hydrogen takes the form: The change in energy due to the 3 0 p term to first order is zero, because 3 0 p is an odd parity function, thus its integral over all space is zero.
The effect of the 4 0 p term is the same as (32) with The second order correction for the 3 0 p term, can be found numerically, for the ground state 100  :

Modified Lorentz force law
Because the GUP modifies the Hamiltonian, one expects that any system with a well-defined Hamiltonian is perturbed [9], perhaps even classical Hamiltonians. The impact of the GUP2-corrected classical Hamiltonian on Newton's gravitational force law was examined in [17]; here, we derive a modified Lorentz force law.
For a particle in an electromagnetic field, the GUP1-modified Hamiltonian is [5]: Using inversion of series: (45) Applying the Euler-Lagrange equation The RHS is ( , which means that the Lorentz force law becomes: which is approximately: Using the same method as above, the GUP2-corrected Hamiltonian takes the form [8]: differentiating w.r.t 0 p and using inversion of series: leading to the Lagrangian: from which we obtain: which is approximately: The new term in (48) and (53) depends on mv , which means that its effect in high energy physics will be too small even at relativistic speeds. For example, in a proton-proton scattering experiment: Experimental tests of Coulomb's law use large, but usually static, masses [18]. For example, coulomb's torsion balance experiment measures the torsion force needed to balance the electrostatic force, and Cavendish's concentric spheres experiment, and its modern counterparts, use two or more concentric spheres, (or cubes, or icosahedra) [18] to test Gauss's law.
To test Eqs. (48) and (53) we need large masses, with moderate velocities. Suppose we have a pendulum with length R and a bob with charge q and mass m swinging above an infinite charged plane with charge density   ; the electric field will be . Without the GUP effect, the bob will experience a force: If  is the angle between the vertical and the string, the equation of motion for small is: Thus, the angular frequency is: However, if we used Eq. (48) for the electrostatic force, then the equation of motion will be: The velocity can be found from conservation of energy, taking the gravitational and electrical potentials to be zero on the plane: where 0  is the initial angle, assuming it starts with zero initial velocity.
The equation of motion will be: Thus, the angular frequency is: And for GUP2 These values, I believe, are accessible with current technology, and thus can be used to set much lower bounds on the GUP parameters than the best bound [19]

Generalized Time-Energy Uncertainty
Suppose a light-clock consists of two parallel mirrors a distance L apart, the time a photon takes to travel from one mirror to the other is: , but length cannot be measured more accurately than the Planck length so: sec , is the Planck time. This shows that the existence of a minimal length scale limits the precision of time measurements. A more rigorous analysis using general relativity, and taking into account the gravitational attraction between the photon and the mirrors, leads to the same conclusion [1,20].
The time-energy uncertainty relation can be obtained from the position-momentum uncertainty relation by using . GUP2 leads to: An important application of the time-energy uncertainty is calculating the mean life of short-lived particles, by using the full width  divided by two as a measure of E  [21], i.e. /     , because  is easier to determine experimentally than . Applying (69) & (70) instead of (68) leads to an extremely small change in the mean life of particles.
In table 2, the mass m and the full width Γ are from [22].  The effect of the generalized time-energy uncertainty principle on the mean life is too small to measure experimentally, but it might affect the Planck era cosmology [23]. In [23] the authors investigate the effect of similar relations to (69) & (70) on the values of the main Planck quantities, like P t , and reach the conclusion that they were lager at the Planck era than now by a factor of 4 (10 10 )  under specific conditions. If true, then the effect of (69) & (70) on the mean life of particles was greater at the early universe, and might leave traces in present day cosmology.

Conclusions
In this paper, we investigated some implications of the GUP1 and GUP2. We calculated the GUP-corrections to the energy of the quantum harmonic oscillator for all energy levels to first and second order perturbation; and although the corrections are small, current and future experiments can be used to set bounds on the values of the GUP parameters. We also found that the difference between corrections due to GUP1 and GUP2 gets bigger with increasing n ; this may provide a way to experimentally determine which GUP is correct.
Then, we investigated the GUP-effect on the spectrum of atomic Hydrogen, because spectroscopy provides increasingly more precise measurements for transition frequencies in atoms. We also found that GUP1 and GUP2 have almost the same effect on the spectrum of Hydrogen.
After that, we investigated how the GUP-corrected classical Hamiltonian leads to a modified Lorentz force law. We also found that it might be possible to detect the effect of the modified Lorentz force law with current technology, unless the GUP is only applicable near the Planck scale.
Finally, we saw how the GUP leads to a generalized time-energy uncertainty principle, and considered it effect on the mean life of some particles, which was too small to measure experimentally. However, its effect in the early universe might be detectable in present day cosmology.

Acknowledgements
I would like to thank Dr. Ahmed Farag Ali for his support, and for the interesting discussions we had on the GUP. I would also like to thank the anonymous referees whose useful comments and suggestions made this paper much better.